Nearest-neighbor Configuration Research Articles

Improvement of strength in low-carbon Nb–Ti weathering steel through Ce microalloying

In this study, a high-strength low carbon Nb–Ti containing weathering steel was developed. The steel achieved a yield strength of 824.4 MPa and an elongation of 24.4% with the addition of 0.030% Ce as a microalloying element. Precipitation strengthening and dislocation strengthening contributed nearly 60% to the yield strength of the steel. The effects of Ce on the dissolution and precipitation behavior of microalloying elements were analyzed through experimental research and first-principles calculations. Additionally, the associated strengthening mechanisms were elucidated. The findings revealed that the Ce–Nb pairs within the 2 to 7 nearest-neighbor configuration in face-centered cubic Fe exhibited a mutual attraction. This attraction promoted the dissolution of microalloyed carbonitrides, leading to a reduction in the volume fraction of precipitates with diameters above 150 nm from 1.3% to 0.62%. Conversely, in the body-centered cubic Fe structure, Ce–Nb atom pairs were mutually repulsive across all configurations. During the coiling process, the addition of Ce increased the formation of nanoprecipitates in the 0.030% Ce–Nb–Ti weathering steel. Particularly, the volume fraction of precipitates with diameters ranging from 20 to 150 nm in the steel increased from 1.6% to 2.7%, while the fraction of nanoprecipitates also increased from 0.051% to 0.31%. The nanoprecipitates formed within the dislocation substructure of the ferrite significantly enhanced steel strength but reduced its plasticity. Additionally, the addition of Ce led to the formation of numerous fine cementite particles in the localized areas of the steel matrix, which contributed up to 49.2 MPa to the overall strength of the steel.

Spin-Stabilization by Coulomb Blockade in a Vanadium Dimer in WSe2.

Charged dopants in 2D transition metal dichalcogenides (TMDs) have been associated with the formation of hydrogenic bound states, defect-bound trions, and gate-controlled magnetism. Charge-transfer at the TMD-substrate interface and the proximity to other charged defects can be used to regulate the occupation of the dopant's energy levels. In this study, we examine vanadium-doped WSe2 monolayers on quasi-freestanding epitaxial graphene, by high-resolution scanning probe microscopy and ab initio calculations. Vanadium atoms substitute W atoms and adopt a negative charge state through charge donation from the graphene substrate. VW-1 dopants exhibit a series of occupied p-type defect states, accompanied by an intriguing electronic fine-structure that we attribute to hydrogenic states bound to the charged impurity. We systematically studied the hybridization in V dimers with different separations. For large dimer separations, the 2e- charge state prevails, and the magnetic moment is quenched. However, the Coulomb blockade in the nearest-neighbor dimer configuration stabilizes a 1e- charge state. The nearest-neighbor V-dimer exhibits an open-shell character for the frontier defect orbital, giving rise to a paramagnetic ground state. Our findings provide microscopic insights into the charge stabilization and many-body effects of single dopants and dopant pairs in a TMD host material.

Effect of chemical disorder on the magnetic anisotropy in L10 FeNi from first-principles calculations

We use first-principles calculations to investigate how deviations from perfect chemical order affect the magnetocrystalline anisotropy energy (MAE) in $L{1}_{0}$ FeNi. We first analyze the local chemical environment of the Fe atoms in various partially ordered configurations, using the orbital magnetic moment anisotropy (OMA) as proxy for a local contribution to the MAE. We are able to identify a specific nearest neighbor configuration and use this ``favorable environment'' to successfully design various structures with MAE higher than the perfectly ordered system. However, a systematic analysis of the correlation between local environment and OMA using smooth overlap of atomic positions indicates only a partial correlation, which exists only if the deviation from full chemical order is not too large, whereas in general no such correlation can be identified even using up to third nearest neighbors. Guided by the observation that the identified favorable environment implies an Fe-rich composition, we investigate the effect of randomly inserting additional Fe into the nominal Ni planes of the perfectly ordered structure. We find that the MAE increases with Fe content, at least up to 62.5% Fe. Thus, our paper shows that the perfectly ordered case is not the one with highest MAE and that an increased MAE can be obtained for slightly Fe-rich compositions.

The Influence of Boron on Microstructural Evolution, Mechanical and Magnetic Behavior of Amorphous Fe91−x(Zr5-Nb4)Bx Melt-Spun Alloys

In this work, we report a systematic study on the microstructure evolution of rapid solidified Fe91−xZr5Nb4Bx alloys (x = 10, 15, 20, 25, 30 at%) under melt-spinning conditions. Mechanical and magnetic properties are also evaluated. X-ray diffraction patterns indicate that the microstructure across the compositional series consists of an amorphous matrix with partial crystallization when boron concentration is increased. These features were identified by transmission electron microscopy (TEM). The radial distribution function (RDF) affords to resolve the nearest-neighbor configuration. The tensile and microhardness properties were measured to correlate the microstructural evolution with boron content. On the other hand, the magnetic properties of these alloy series were determined by vibrating sample magnetometry (VSM); the saturation magnetization and Curie temperature showed an increasing tendency when increasing the boron content, reaching values up to 110 Am2kg−1 and 465 K, respectively. In addition to the aforementioned, the coercive field remained constant. All these magnetic properties were correlated with the microstructure features observed by XRD, RDF and TEM.

Array enhanced stochastic resonance for augmented energy harvesting

Research studies on vibration energy harvesting have shown from time to time that bistable harvesters offer a lucrative solution for harnessing substantial magnitude of power across a broad range of frequencies. This exciting potential of bistable harvesters has bred interest towards investigating the possibility of enhancement in power by coupling multiple of them. In this regard, the present work analyzes the behavior of a 1-D array of bistable piezoelectric harvesters mechanically coupled in the nearest-neighbor configuration under a noise perturbed periodic base excitation. The numerical study reports a resonant-like behavior of the total power with system size for certain noise levels of excitation. The parametric regimes to which the system size resonance effect is confined have been identified. The present work attempts to provide an intuitive understanding into the role of system size on the total harvested power under a noisy environment. Inferences drawn from the results of this work shall help in designing a harvesting system to realize broadband power generation.

Effect of the number of defect particles on the structure and dispersion relation of a two-dimensional dust lattice system

The effect of the number of defect particles on the structure and dispersion relations of a two-dimensional (2D) dust lattice is studied by molecular dynamics (MD) simulation. The dust lattice structures are characterized by particle distribution, nearest neighbor configuration and pair correlation function. The current autocorrelation function, the dispersion relation and sound speed are used to represent the wave properties. The wave propagation of the dust lattice closely relates to the lattice structure. It shows that the number of defect particles can affect the dust lattice local structure and then affect the dispersion relations of waves propagating in it. The presence of defect particles has a greater effect on the transverse waves than on the longitudinal waves of the dust lattice. The appropriate number of defect particles can weaken the anisotropy property of the lattice.

Determination of Vacancy Formation Energies in Binary UZr Alloys Using Special Quasirandom Structure Methods

The use of predictive models to examine defect production and migration in metallic systems requires a thorough understanding of the energetics of defect formation and migration. In fully miscible alloys, atomistic properties will all have a range of values that are heavily dependent on local atomic configurations. In this work we have used the atomistic simulation tool Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) to investigate the impact of first nearest neighbor configuration on vacancy formation energies at 0 K in γ-U-Zr alloys of varying Zr concentrations. The properties of randomly generated alloy microstructures were also compared with those produced as special quasi-random structures (SQS) using the “mcsqs” code within the Alloy Theoretic Automated Toolkit. Results have confirmed that local configuration can have a significant impact on measured properties and must be considered when characterizing miscible alloy systems. Results also indicated that the generation method of the random structure (i.e., via random species assignment or a method of enforced randomness) does not result in a measurable difference in average vacancy formation energies in miscible U-Zr systems.

Accelerated Adaptive Fuzzy Optimal Control of Three Coupled Fractional-Order Chaotic Electromechanical Transducers

In this article, we investigate the issue of the accelerated adaptive fuzzy optimal control of three coupled fractional-order chaotic electromechanical transducers. A small network where every transducer has the nearest-neighbor coupling configuration is used to form the coupled fractional-order chaotic electromechanical transducers. The mathematical model of the coupled electromechanical transducers with nearest-neighbors is established and the dynamical analysis reveals that its behaviors are very sensitive to external excitation and fractional order. In the controller design, the recurrent nonsingleton type-2 sequential fuzzy neural network (RNT2SFNN) with the transformation is designed to estimate unknown functions of dynamics system in the feedforward fuzzy controller, and it is constructed to approximate the critic value and actor control functions by using policy iteration (PI) in the optimal feedback controller. Meanwhile, the speed functions are employed to achieve accelerated convergence within a pregiven finite time and a tracking differentiator is used to solve the explosion of terms associated with traditional backstepping. The whole control strategy consists of a feedforward controller integrating with the RNT2SFNN, tracking differentiator, and speed function in the framework of the backstepping control and a feedback controller fusing with the RNT2SFNN and PI under an actor/critic structure to solve the Hamilton–Jacobi–Bellman equation. The proposed scheme not only guarantees the boundness of all signals and realizes the chaos suppression, synchronization, and accelerated convergence, but also minimizes the cost function. Simulations demonstrate and validate the effectiveness of the proposed scheme.

Synchronization characteristics of an array of coupled MEMS limit cycle oscillators

The dynamics of a proposed microelectromechanical system (MEMS) consisting of an array of limit cycle oscillators (LCOs) are analyzed. The LCOs have dissimilar limit cycle frequencies and are coupled in a nearest-neighbor configuration via electrostatic fringing fields. The emergence of synchrony in the array is outlined for two cases: self-synchronization of the array to a single frequency, and entrainment of the array to an external inertial drive. Numerical analysis is used to study the dependence of synchrony on system parameters such as the coupling strength, detuning in the array, inertial drive strength, and frequency of the inertial drive. It is shown that the route to synchrony is complex due to the formation of frequency clusters. The limit cycle frequency of a single equivalent oscillator, with parameters averaged over the array is used as an estimate for the frequency of locking for the array. This equivalent oscillator is used to approximate the entire array and perturbation methods are applied to it. The perturbation method qualitatively captures the entrainment characteristics of the externally-driven array. This analysis is also used to track the complex sequence of bifurcations that occur as the drive strength changes, and to estimate the threshold drive strength for entrainment.

Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

AbstractThe oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O2 adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.

Reverse-nearest neighborhood based oversampling for imbalanced, multi-label datasets

In this article, we present a novel reverse-nearest neighborhood based oversampling scheme for the imbalanced labels of a multi-label dataset. Reverse nearest neighborhood of a query point includes all those points which contain the query point as one of their neighbor. It facilitates us to identify an adaptive number of neighbors (according to the density and distribution of points) instead of a fixed number of neighbors. We add label-specific synthetic minority instances in the reverse nearest neighborhood of the minority points of each label. Reverse nearest neighbor configuration also detects the singular minority points, which we avoid as seed points in the oversampling phase. On the oversampled data of each label, we train and invoke a Linear Support Vector Machine to complete the learning and testing. Results of the proposed method against comparing methods on class-imbalance focused metrics indicates its competence in handling differently imbalanced multi-label datasets.

Strong Interplay between Sodium and Oxygen in Kesterite Absorbers: Complex Formation, Incorporation, and Tailoring Depth Distributions

AbstractSodium and oxygen are prevalent impurities in kesterite solar cells. Both elements are known to strongly impact performance of the kesterite devices and can be connected to efficiency improvements seen after heat treatments. The sodium distribution in the kesterite absorber is commonly reported, whereas the oxygen distribution has received less attention. Here, a direct relationship between sodium and oxygen in kesterite absorbers is established using secondary ion mass spectrometry and explained by defect analyses within the density functional theory. The calculations reveal a binding energy of 0.76 eV between the substitutional defects NaCu and OS in the nearest neighbor configuration, indicating an abundance of NaO complexes in kesterite absorbers at relevant temperatures. Oxygen incorporation is studied by introducing isotopic 18O at different stages of the Cu2ZnSnS4/Mo/soda‐lime glass baseline processing. It is observed that oxygen from the Mo back contact and contaminations during the sulfurization are primary contributors to the oxygen distribution. Indeed, unintentional oxygen incorporation leads to immobilization of sodium. This results in a strong correlation between sodium and oxygen, in excellent agreement with the theoretical calculations. Consequently, oxygen availability should be monitored to optimize postdeposition heat treatments to control impurities in kesterite absorbers and ultimately, the solar cell efficiency.

Self-assembly of biological networks via adaptive patterning revealed by avian intradermal muscle network formation

Networked structures integrate numerous elements into one functional unit, while providing a balance between efficiency, robustness, and flexibility. Understanding how biological networks self-assemble will provide insights into how these features arise. Here, we demonstrate how nature forms exquisite muscle networks that can repair, regenerate, and adapt to external perturbations using the feather muscle network in chicken embryos as a paradigm. The self-assembled muscle networks arise through the implementation of a few simple rules. Muscle fibers extend outward from feather buds in every direction, but only those muscle fibers able to connect to neighboring buds are eventually stabilized. After forming such a nearest-neighbor configuration, the network can be reconfigured, adapting to perturbed bud arrangement or mechanical cues. Our computational model provides a bioinspired algorithm for network self-assembly, with intrinsic or extrinsic cues necessary and sufficient to guide the formation of these regenerative networks. These robust principles may serve as a useful guide for assembling adaptive networks in other contexts.

Mean field treatment of heterogeneous steady state kinetics

We propose a method to quickly compute steady state populations of species undergoing a set of chemical reactions whose rate constants are heterogeneous. Using an average environment in place of an explicit nearest neighbor configuration, we obtain a set of equations describing a single fluctuating active site in the presence of an averaged bath. We apply this Mean Field Steady State (MFSS) method to a model of H2 production on a disordered surface for which the activation energy for the reaction varies from site to site. The MFSS populations quantitatively reproduce the KMC results across the range of rate parameters considered.

Structure and magnetic properties of amorphous Fe-(Zr,Nb)-B melt spun alloys

In this work, we report the structure and magnetic behavior of an amorphous Fe81Zr5Nb4B10 melt-spun alloy. The radial distribution function (RDF) afforded the resolution of the nearest-neighbor configuration on the basis of the atom-pair distance information, for which the positions of each peak indicated the atom-to-atom separation involved for short-range ordering. The first peaks of RDF were attributed to the distances of B-B, Fe-Fe and Zr-Nb atomic pairs, indicating a glassy structure equivalent to a distorted bcc-Fe cluster. From magnetic measurements, a magnetic moment of 0.65 Bohr magneton per Fe atom was established, together with a Curie temperature of 334 K and an initial ac permeability of 550 for frequencies as high as 250 kHz. In addition, the magnetocaloric effect, quantified from isothermal magnetization measurements through the magnetic entropy variation, reached a maximum of 2.0 J/kgK for a magnetic field change of 2.0 T.

First-principles study of the magnetism of Ni-doped MoS2 monolayer

The magnetic properties of Ni-doped monolayer MoS2 are investigated using the density function theory. The results show that two Ni-doped systems of the nearest-neighbor configuration are ferromagnetic. The p–d hybridization between the Ni dopant and its neighboring S atoms results in the splitting of energy levels near the Fermi energy. These results suggest the p–d hybridization mechanism for the magnetism of the Ni-doped MoS2 monolayer. The magnetic moment disappears with increasing Ni–Ni distance. Our studies predict the nearest two-Ni-doped MoS2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations indicate that it would be easier to incorporate Ni atoms into a S-rich MoS2 monolayer in the experiment.

Magnetostatic Interactions in Self-Assembled CoxNi1-xFe2O4/BiFeO3 Multiferroic Nanocomposites.

Self-assembled vertically aligned oxide nanocomposites consisting of magnetic pillars embedded in a ferroelectric matrix have been proposed for logic devices made from arrays of magnetostatically interacting pillars. To control the ratio between the nearest neighbor interaction field and the switching field of the pillars, the pillar composition CoxNi1-xFe2O4 was varied over the range 0 ≤ x ≤ 1, which alters the magnetoelastic and magnetocrystalline anisotropy and the saturation magnetization. Nanocomposites were templated into square arrays of pillars in which the formation of a "checkerboard" ground state after ac-demagnetization indicated dominant magnetostatic interactions. The effect of switching field distribution in disrupting the antiparallel nearest neighbor configuration was analyzed using an Ising model and compared with experimental results.

Magnetostatic nearest neighbor interactions in a Co48Fe52 nanowire array probed by in-field magnetic force microscopy

The magnetization behavior of nanowires embedded in an array is influenced by the sum of the dipolar fields produced by all surrounding nanowires. These magnetostatic interactions largely modify the array properties and thus complicate the reconstruction of the ensemble averaged behavior of the individual nanowires, such as the intrinsic switching field distribution. Simply correcting the shearing of the hysteresis in a mean-field approach does not account for the locally fluctuating demagnetizing field, which originates from the individual magnetization configuration in the close surrounding of each nanowire. We present an in-field Magnetic Force Microscopy study of electrochemically produced Co48Fe52 nanowires, in which the influence of the magnetic nearest neighbor configuration on the switching behavior of the individual embedded nanowires is clearly detected. Based on this finding, a statistical evaluation method of nearest neighbor histograms is proposed, which potentially allows to judge the strength of the local magnetostatic interactions against the magnitude of the intrinsic switching field distribution.

Electronic and magnetic properties of X-doped (X = Ti, Zr, Hf) tungsten disulphide monolayer

Based on density functional theory, we investigated electronic and magnetic properties of X-doped (Group 4) WS2 monolayer for 6.25% and 12.5% X concentration. Numerical results show that one X-doped WS2 monolayer is non-magnetic, while two X-doped systems of the next nearest neighbor configuration are ferromagnetic (FM). The hybridization between the X dopant and its neighboring W and S atoms results in the splitting of the energy levels near the Fermi energy. These results suggest the p(d)–d(d) hybridization mechanism for the magnetism of the X-doped WS2 monolayer structures. The asymmetric charge density distribution induces to magnetism for two next nearest neighbor X-doped WS2 systems. The studies find that the two next nearest X-doped WS2 monolayers to be candidates for magnetic metallic material. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate X atom into the WS2 monolayer under S-rich experimental conditions. Our results show that substitutional doping from IVB group is an effective way to modulate electronic and magnetic properties of tungsten disulphide monolayer.

Magnetic properties of two nearest Cu-doped monolayer WS 2 : A first-principles study

Abstract We investigate magnetic properties of Cu-doped monolayer WS 2 for 6.25%, 8% and 12.5% Cu concentration using the first-principles methods based on density functional theory. The results show that one Cu-doped monolayer WS 2 is non-magnetic, while two Cu-doped systems of the nearest neighbor configuration are ferromagnetic (FM). The hybridization between the Cu dopant and its neighboring S atoms results in the splitting of the energy levels near the Fermi energy. These results suggest the p – d hybridization mechanism for the magnetism of the Cu-doped WS 2 monolayer structures. While the magnetic moment disappears with the increasing Cu–Cu distances. Our studies predict the nearest two Cu-doped WS 2 monolayers to be candidates for thin dilute magnetic semiconductors. Moreover, the formation energy calculations also indicate that it is energy favorably and relatively easier to incorporate Cu atom into the WS 2 monolayer under S-rich experimental conditions.