Atomic Spacing Research Articles

Determining Homogenization Parameters and Predicting 5182-Sc-Zr Alloy Properties by Artificial Neural Networks.

Artificial neural networks (ANNs) were established for the homogenization and recrystallization heat treatment processes of 5182-Sc-Zr alloy. Microhardness and conductivity testing were utilized to determine the precipitation state of Al3(ScxZr1-x) dispersoids during the homogenization treatment, while electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to observe the microstructure evolution of the alloy. Tensile experiments were performed to test the mechanical properties of the alloy after recrystallization annealing. The two-stage homogenization parameters were determined by studying the changes in microhardness and electrical conductivity of 5182-Sc-Zr alloy after homogenization with the assistance of artificial neural networks: the first-stage homogenization at 275 °C for 20 h and the second-stage homogenization at 440 °C for 12 h. The dispersoids had entirely precipitated after homogenization, and the alloy segregation had improved. A high-accuracy prediction model, incorporating multiple influencing factors through artificial neural networks, was successfully established to predict the mechanical properties of the 5182-Sc-Zr alloy after annealing. Based on the atomic plane spacing in HRTEM, it was determined that the Al3(ScxZr1-x) dispersoids and the Al matrix maintained a good coherence relationship after annealing at 400 °C.

B-direction anomalous thermal expansion behavior in SmCrO3

The ceramic composites of Sm1-xBixCrO3 (x = 0, 0.1, 0.2, 0.3) have been prepared by solid state reaction. X-ray diffraction patterns demonstrate that Bi-doped polycrystalline samples match with standard pattern of SmCrO3. After Bi doping, the lattice constants in three directions increase slightly. The thermal expansion properties were studied by X-ray powder diffraction over the temperature range from 100 to 400 K. The results showed that the compound SmCrO3 exhibits positive thermal expansion behavior in the a and c directions in the whole measurement temperature range. The anomaly is that in the b direction the lattice exhibits positive thermal expansion behavior at low temperatures, while above 200 K it exhibits near zero thermal expansion behavior. The thermal expansion behaviors of all Bi-doped SmCrO3 are similar to that of SmCrO3, but unexpectedly, negative thermal expansion behaviors were observed in the b direction above 200 K in the highly Bi doped samples. The dielectric measurement shows that there are two thermal activation processes in all Sm1-xBixCrO3 (x = 0, 0.1, 0.2, 0.3) respectively, with the low-temperature activation corresponding to the grain itself, while the high-temperature activation comes from the grain boundary. After low-temperature thermal activation, with increasing temperature, the enhanced vibration of the corner oxygen atoms of the CrO6 octahedron is mainly perpendicular to the b axis, which leads to the near zero thermal expansion behavior in the b direction. Moreover, after high-temperature thermal activation, as the temperature increases, the enhanced interaction between Bi3+ and the free oxygen atom (space oxygen atom) at the grain boundary will further lead to the negative thermal expansion behavior in the b-direction of the high concentration doped samples.

Tuning Active Metal Atomic Spacing by Filling of Light Atoms and Resulting Reversed Hydrogen Adsorption-Distance Relationship for Efficient Catalysis

HighlightsDensity functional theory calculations indicates that interstitial B atoms can tune the atomic spacing of host metal Os and achieve a reversal hydrogen adsorption-distance relationship.The structure–activity relationship between the spacing of active Os atoms and catalytic activity is established.Prepared OsB2 with increasing dOs-Os of 2.96 Å presents the optimal hydrogen evolution reaction activity (8 mV @ 10 mA cm−2) and robust stability in alkaline media.

Investigation of structure and soot formation in laminar inverse diffusion flames by atomic ratio measurements using laser-induced breakdown spectroscopy

This experimental study reports the two-dimensional C/O and H/O atomic ratio distributions of oxy-ethylene laminar inverse diffusion flames (IDFs) with elevated stoichiometric mixture fractions (Zst) using laser-induced breakdown spectroscopy (LIBS), and investigates the effects of Zst on the structure and soot formation of IDFs. The LIBS diagnostic system consisting of a pulsed Nd: YAG laser and a fiber optic spectrometer measures the atomic ratios of IDFs with Zst of 0.2–0.5, and the influence of laser energy on atomic ratio calibrations and measurements is corrected to improve accuracy. IDFs are divided into five zones, namely the oxidant zone, the chemiluminescence zone, the gap, the soot zone, and the fuel zone. The C/O atomic ratio of the chemiluminescence zone and the gap remains 0.35–0.5, and the soot zone is 0.4–0.7. Except for the gap, where the H/O atomic ratio remains at 0.55–0.60, the H/O atomic ratio of all other zones is greatly affected by Zst. These atomic ratio results demonstrate that the C/O atomic ratio has the advantage of differentiating the structure of IDFs. Experimental results show a C/O atomic ratio of 0.5–0.6 is required for soot inception in IDFs, so the elevated Zst delays soot inception by lowering the C/O atomic ratio near the flame sheet, and it also compresses the residence time and C/O atomic ratio space favorable for soot formation. Additionally, the decreased local equivalence ratio determined from the H/O atomic ratio further confirms that the increase of Zst makes IDFs unsuitable for soot formation. This study proves that LIBS is an effective flame diagnostic tool and the atomic ratios hold promise for studying a broader range of flame configurations.

Microcrack initiation and propagation in 3 C-SiC ceramic based on molecular dynamics nano-drilling

The evolutionary mechanism of microcracking has been the focus of research in materials processing. The experimental calculation and analysis of microcracking are inevitably difficult due to the limitations of the controllability of its emergence and expansion and the existing observation techniques. In this paper, an experimental model of nano-drilling of 3 C-SiC ceramic parts is constructed using molecular dynamics simulations to achieve real-time observation of the drilling process at the atomic scale, and the microcrack evolution behavior at different depths during the drilling process is discussed, and the microcrack initiation and propagation laws of 3 C-SiC ceramic drilling processing are proposed. The results show that when drilling reaches a certain depth, the compressive stress generated by drilling leads to a prominent region in the plastic deformation zone below the drill bit, where the atomic spacing becomes larger and the workpiece material splits, forming a microcrack eruption zone. The expansion direction of the microcrack is related to the dislocation slip direction, and it expands continuously with the continuous emission of dislocations at the crack tip. The influence of the special evolutionary behavior of the dislocation ring on the microcrack expansion during drilling is focused on, and it is found that the trend of microcrack expansion changed due to the creation of the dislocation ring, and the limit of microcrack expansion is significantly correlated with the dislocation ring evolutionary behavior. With the drilling simulation, the new microcrack expansion showed a periodic occurrence pattern with the special evolutionary behavior of dislocation rings.

Distance controlled graphyne-like binuclear palladium catalyst for accelerating nitrobenzene reduction

The diatomic catalyst synthesized by high-temperature thermal cracking usually undergoes structural reorganization of raw materials, increasing the difficulty in studying the structure-activity relationship of the catalysts. Herein, starting from the synthesis methodology, we adjust the atomic spacing of dual-Pd-site catalysts to 0.4 and 0.8 nm by regulating the monomer structure of graphyne. The model experiment of nitrobenzene reduction shows that graphyne catalyst (TEGY-Pd) with closer palladium atom spacing (0.4 nm) show a faster reaction rate (1.57 min−1), good universality and cyclic stability in catalytic process than that of graphdiyne catalyst (TEGDY-Pd) which has longer palladium atom spacing. Moreover, the theoretical calculation shows that the excellent catalytic performance of TEGY-Pd is original from the synergetic catalysis of the closer diatomic palladium to the nitro group in adsorption and electron transport process. This work provided a new idea to precisely control the metal atomic spacing and revealed the structure activity relationship of binuclear catalysts.

Spectroscopic Characterization, Cyclic Voltammetry, Biological Investigations, MOE, and Gaussian Calculations of VO(II), Cu(II), and Cd(II) Heteroleptic Complexes.

A novel hydrazone ligand (o-H2BMP) N-(benzo[d]thiazol-2-yl)-3-oxo-3-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)propanamide alongside its Cu(II), Cd(II), and VO(II) complexes were prepared and structurally characterized via various spectroscopic analyses (Fourier transform infrared spectroscopy, UV-visible spectroscopy, 1H/13C NMR spectroscopy, liquid chromatography coupled to mass spectrometry, and electron paramagnetic resonance spectroscopy) as well as by elemental analysis, thermal gravimetry analysis/differential thermal analysis, and magnetic moment measurements. Powder X-ray diffraction analysis was also performed for the free ligand and its metal complexes to determine the crystallographic structures and atomic spacing. It also provided information on unit cell dimensions and the average crystallite size. Furthermore, geometric optimization and computational studies were carried out by applying Gaussian (09) software based on density-functional theory coupled with the B3LYP functional and LANL2DZ/6-31+G(d,p) mixed basis set to evaluate some distinct features such as molecular electrostatic potential, E HOMO, and E LUMO. Moreover, electrochemical measurements were performed for Cu(II) in the absence/presence of the chelating agent to predict the effect of complexation interaction in the solution state study. As part of the biological examination, antioxidant and antimicrobial assays were conducted for each compound individually, in addition to cytotoxicity evaluations via MTT assays for all isolated complexes compared to the corresponding metal salts. The MOE (molecular operating environment) approach was also applied to model the interface between the isolated compounds and proteins that were expressed in breast cancer at the atomic level.

Vacancy engineering in Co-doped CuS1-x with fast Electronic/Ionic migration kinetics for efficient Lithium-Ion batteries

Slow Li ion diffusion kinetics and disordered migration of electrons are two most crucial obstacles to be resolved in electrode material design for higher rate capability of Li-ion batteries. Herein, the Co-doped CuS1-x with abundant high active S vacancies is proposed to accelerate the electronic and ionic diffusion during the energy conversion process, because contraction of Co-S bond can cause the expansion of atomic layer spacing, thus promoting the Li ion diffusion and directional electron migration parallel to the Cu2S2 plane, and also induce the increasing of active sites to improve the Li+ adsorption and electrocatalytic conversion kinetics. Especially, the electrocatalytic studies and plane charge density difference simulations demonstrate that electron transfer near the Co site is more frequent, which is conducive to more rapid energy conversion and storage. Those S vacancies formed by Co-S contraction in CuS1-x structure obviously increase Li ion adsorption energy in Co-doped CuS1-x to 2.21 eV, higher than the 2.1 eV for CuS1-x and 1.88 eV for CuS. Taking these advantages, the Co-doped CuS1-x as anode of Li-ion batterie shows an impressive rate capability of 1309 mAh·g−1 at 1A g−1, and long cycling stability (retaining 1064 mAh·g−1 capacity after 500 cycles). This work provides new opportunities for the design of high-performance electrode material for rechargeable metal-ion batteries.

Efficient deoxygenation of methyl esters to hydrocarbons on Al2O3 supported Ni-Sn intermetallic compounds

Al2O3 supported Ni-Sn alloy (Ni/Sn atomic ratio of 6) and Ni3Sn, Ni3Sn2 and Ni3Sn4 intermetallic compounds (IMCs) were prepared by co-precipitation method for the deoxygenation of fatty acid methyl esters to produce hydrocarbons. In comparison with metallic Ni, the catalytic evaluation and methyl propionate-TPD/TPSR results reveal that Ni-Sn IMCs remarkably inhibit the decarbonylation/decarboxylation pathway, C-C bond hydrogenolysis and methanation while promote the hydrodeoxygenation pathway, subsequently enhancing the yield of aiming hydrocarbons. Therein, 20%Ni3Sn2/Al2O3 has the best performance, and the hydrocarbons yield reach about 99% in the deoxygenation of methyl octanoate and methyl palmitate. We suggest that the geometric and electronic effects of Sn contribute the excellent performance of Ni-Sn IMCs, and there is synergetic effect between Ni and Sn sites for the activation of C-O/C=O bond, for which a suitable Ni-Sn atomic spacing is very important. Finally, the catalyst stability and deactivation were also investigated.

Atomic decompositions for noncommutative martingales

We prove an atomic type decomposition for the noncommutative martingale Hardy space hp for all 0<p<2 by an explicit constructive method using algebraic atoms as building blocks. Using this elementary construction, we obtain a weak form of the atomic decomposition of hp for all 0<p<1, and provide a constructive proof of the atomic decomposition for p=1 which resolves a main problem on the subject left open for the last twelve years. We also study (p,∞)c-atoms, and show that every (p,2)c-atom can be decomposed into a sum of (p,∞)c-atoms; consequently, for every 0<p≤1, the (p,q)c-atoms lead to the same atomic space for all 2≤q≤∞. As applications, we obtain a characterization of the dual space of the noncommutative martingale Hardy space hp (0<p<1) as a noncommutative Lipschitz space via the weak form of the atomic decomposition. Our constructive method can also be applied to prove some sharp martingale inequalities.

Epitaxial growth of a β-Ga2O3 (−201)-oriented thin film on a threefold symmetrical SrTiO3 (111) substrate for heterogeneous integration

Epitaxial growth of a wide bandgap semiconductor β-Ga2O3 thin film with high crystal quality plays a decisive role in constructing optical and electronic devices. However, except for the native substrate, the scarcity of appropriate non-native substrates or the poor crystallization of the deposit in thin film growth severely limits the fabrication and applicability of the final heterostructures and devices. Here, by taking the consistent symmetry and closely matched atomic spacing between β-Ga2O3 (−201) and the cubic perovskite (111)-oriented plane of SrTiO3, we realize the epitaxial growth of single crystal β-Ga2O3 (−201) thin films on the SrTiO3 (111) substrate by the pulsed laser deposition method, as confirmed by wide-range reciprocal-space mapping and high-resolution scanning transmission electron microscopy. The fabricated β-Ga2O3 (−201) photodetector device on the SrTiO3 (111) substrate exhibits excellent ultraviolet optical detection performance with large on/off switching ratios and a fast response speed. Moreover, the β-Ga2O3/SrTiO3 (111) heterojunction shows type-II heterostructure characteristics for energy band alignment, which displays superior ability for electron–hole pairs separation with large conduction and small valance band offsets of 1.68 and 0.09 eV, respectively. The results offer us a new way to obtain high-quality β-Ga2O3 (−201) thin film heterostructures on cubic SrTiO3 (111) substrates and fabricate β-Ga2O3-based optical and electronic devices.

An extension of the $\mathrm{VMO}$-$H^1$ duality

In 1977, Coifman and Weiss gave a proof of the $\mathrm{VMO}$-$H^1$ duality. We consider generalized Campanato spaces and atomic Hardy spaces with variable growth condition and give an extension of the duality to these spaces. We also apply this duality to the Riesz transforms.

Constructing Collective Variables Using Invariant Learned Representations.

On the time scales accessible to atomistic numerical modeling, chemical reactions are considered rare events. Therefore, the atomistic simulations are commonly biased along a low-dimensional representation of a chemical reaction in an atomic structure space, i.e., along the collective variables. However, suitable collective variables are often complicated to guess a priori. We propose a novel method of collective variable discovery based on dimensionality reduction of the atomic representation vectors. These linear-scaling and invariant representations can be either fixed (untrained) or learned by supervised training of the end-to-end machine learning potential. The learned representations are expected to reflect not only the structural but also the energetic features of the system that are transferable to all of the reactive transformation covered by the machine learning potential. We demonstrate our approach on four high-barrier reactions ranging from a simple gas-phase hydrogen jump reaction to complex reactions in periodic models of industrially relevant heterogeneous catalysts. High data efficiency, automatized feature extraction, favorable scaling, and retention of inherent invariances are all properties that are expected to enable fast and largely automatic construction of suitable collective variables even in highly complex reactive scenarios such as reactive/catalytic transformations at solid-liquid interfaces.

First principles study of structural and electron properties in scorodite: the bulk and surface.

Scorodite (FeAsO4·2H2O) is an ideal material for the fixation of arsenic that has attracted considerable research interest in recent decades. However, the position of the H atom in the scorodite crystal structure, water molecular configuration, surface morphology, and chemical state of the surface atoms have not been reported. In this work, density functional theory (DFT) is used to optimize the scorodite crystal structure, and the atomic bonding is analyzed. At the same time, a surface model is constructed to calculate the configuration and electronic structure of the surface atoms for different coordination groups. The results show that the tetrahedral [AsO4] and octahedral [FeO4(2H2O)] groups in the scorodite crystal structure have good stability(geometry configuration), and the covalent bond strength between the As atom and the bridged oxygen atom (Ob) is greater than that between the Ob atom and the Fe atom. The water molecules in the crystal structure do not seriously deform and ionize. The configuration of the water molecules remains stable through electrostatic interactions (Ow-Fe) and hydrogen bonding (H-Ob). The Fe atoms on the surface of scorodite can coordinate with OH and H2O, while the As atoms can only form a stable coordination with OH. When an Fe atom on the surface coordinates with two H2O atoms, the Fe atom will shrink to the inside of the bulk. With the increase in the hydroxylation number of the Fe atom, the bonding strength between the Fe atom and the Ob atom decreases. Different surface configurations do not affect the stability(geometry configuration) of the [AsO4] structure. In addition, the surface water molecular layer has a very weak effect on the surface coordination configuration. By contrast, in the surface configuration of the (W + OH) structure, the change in the surface atomic layer spacing is the smallest.

Strongly recurrent transformation groups

We define the notions of strong and strict recurrency for actions of countable ordered groups on σ-finite non atomic measure spaces with quasi-invariant measures. We show that strong recurrency is equivalent to non existence of weakly wandering sets of positive measure. We also show that for certain p.m.p ergodic actions the system is not strictly recurrent, which shows that strong and strict recurrency are not equivalent.

Electroreduction of CO 2 to C 2 H 4 Regulated by Spacing Effect: Mechanistic Insights from DFT Studies

It is crucial to construct an efficient catalyst with high activity and excellent selectivity for realizing CO 2 electroreduction reaction (CO 2 ER) to high-value-added chemicals, especially the C2 products. Density functional theory (DFT) provides a powerful tool for investigating the promotional effect on C2 selectivity of finely tuned catalyst structures, which is currently difficult to control using experimental techniques, such as interatomic distances. In the work, 5 Cu 2 O catalyst models are constructed with different Cu-Cu atomic spacing ( d Cu - Cu ). The results of DFT calculations show that adjusting the d Cu - Cu can effectively tailor the electronic structures of active sites, enhance catalytic activity, and improve product selectivity. Specifically, the Cu atom pair spaced at d Cu - Cu = 2.5 Å could optimize the adsorption configuration of *CO and enhance the binding strength of *CO, thus improving *CO adsorption energy and reducing the energy barrier of C-C coupling. The work proves the feasibility of spacing effect in enhancing the C 2 H 4 selectivity of CO 2 ER and provides a new idea for the catalyst modification for other reactions of polyprotons-coupled electrons.

WCK 4873 (INN: Nafithromycin): Structure–activity relationship (SAR) identifying a novel lactone ketolide with activity against Streptococcus pneumoniae (SPN) and Streptococcus pyogenes (SPY)

Ketolides are the fourth generation semisynthetic macrolides derived from erythromycin A, designed to address the limitations of currently available drug treatments including penicillins, macrolides and glycopeptides. Ketolides-the next generation macrolides antibiotics are deliberate to pass the issues of bacterial resistance by introducing keto function at C3 position of macrocycle through the replacement of l-cladinose sugar moiety and brings a broader spectrum of activity. The original research work reported here covers, structure activity relationship based design and synthesis of 34 novel ketolide molecules, are subsequently subjected to desired microbial evaluations. Through this exercise; WCK 4873 (Nafithromycin) has been emerged as clinical candidate among the four different series synthesized. Nafithromycin, consists of novel amidoxime function bearing 2-pyridine-1,3,4-thiadiazole biaryl side chain set apart through a four atom spacer containing a cis double bond and a chiral methyl. This non-flexible spacer possibly aligns the biaryl ring system resulting in a favorable interaction with dual 23S rRNA targets exhibiting better potency to treat gram positive infections. WCK 4873 emerged as preclinical candidate based on in vitro studies, and animal model studies, it had successfully accomplished phase 1 and phase 2 clinical studies in United States, Europe and India. Currently, nafithromycin has acquired the status as phase 3 drug candidate having potential to fulfill the unmet medical needs for treatment of CABP infections.

Nuclear quantum effects in fullerene-fullerene aggregation in water.

We studied the effects of the quantum delocalization in space of the hydrogen atoms of water in the aggregation process of two fullerene molecules. We considered a case using a purely repulsive water-fullerene interaction, as such a situation has shown that water-mediated effects play a key role in the aggregation process. This study becomes feasible, at a reduced computational price, by combining the path integral (PI) molecular dynamics (MD) method with a recently developed open-system MD technique. Specifically, only the mandatory solvation shell of the two fullerene molecules was considered at full quantum resolution, while the rest of the system was represented as a mean-field macroscopic reservoir of particles and energy. Our results showed that the quantum nature of the hydrogen atoms leads to a sizable difference in the curve of the free energy of aggregation; that is, that nuclear quantum effects play a relevant role.

Effective self-healing behavior of nanocrystalline-amorphous laminated alloy under irradiation

An extensive investigation on the microstructural evolution of nanocrystalline–amorphous laminated alloys (NALAs) by molecular dynamics simulations and mechanistic analysis have been conducted to apprehend the interplay of complex phenomena governing structural changes in this alloy under neutron irradiation. It was discovered from the evolution profiles of free volumes, atomic unfilled spaces, and irradiation-induced vacancies that the profound structural response of the NALA was orchestrated by the rapid and spontaneous recovery of free volumes that indicate a self-healing ability in the amorphous zone, while the phenomenon of geometric atomic reconstitution in local structures governs the effective self-healing capacity for annihilated nanocrystal regions. Furthermore, a distinctive, self-migration/diffusion capture dynamics for the annihilation of defects by phase boundaries was discovered as an effective self-healing mechanism in NALAs. These findings will potentially facilitate the development of advanced nuclear materials with high irradiation resistance.

Aharonov-Bohm Caging and Inverse Anderson Transition in Ultracold Atoms.

Aharonov-Bohm (AB) caging, a special flat-band localization mechanism, has spurred great interest in different areas of physics. AB caging can be harnessed to explore the rich and exotic physics of quantum transport in flatband systems, where geometric frustration, disorder, and correlations act in a synergetic and distinct way than that in ordinary dispersive band systems. In contrast to the ordinary Anderson localization, where disorder induces localization and prevents transport, in flat band systems disorder can induce mobility, a phenomenon dubbed inverse Anderson transition. Here, we report on the experimental realization of the AB cage using a synthetic lattice in the momentum space of ultracold atoms with tailored gauge fields, and demonstrate the geometric localization due to the flat band and the inverse Anderson transition when correlated binary disorder is added to the system. Our experimental platform in a many-body environment provides a fascinating quantum simulator where the interplay between engineered gauge fields, localization, and topological properties of flat band systems can be finely explored.