A localized orbital description of Si

Demand for high-performance rechargeable batteries has driven the development of novel electrodes with high reversibility and energy density. Tracking the change in electronic and local structure is crucial to investigate and improve the stability and performance of these batteries. Advanced characterization techniques allow the user to monitor electronic and local atomic structure changes to better understand the role and behavior of different elements during cycling of electrode material for rechargeable batteries.X-ray Absorption and Emission Spectroscopy allow us to explore such changes in 3d transition metal elements through the process of generation and quenching of core holes in the sample. Operando measurements enable real-time monitoring of electronic structure changes in electrode materials which enable us to capture phenomena which are only kinetically accessible.In this study, the change in electronic structure of transition metals present in electrode materials is explored as a function of lithium removal through XES Kβ1,3feature along with K-edge XAFS using a lab-scale instrument. The choice of electrodes explored in this study considers the degree of oxidation, structure, and mechanism for ion storage. Change in peak and edge positions of Kβ1,3and K-edge feature is utilized to monitor oxidation/spin changes in electrode materials during charge/discharge. Further the magnetic behavior for ex-situ samples prepared by electrochemical delithiation of LCO in the range of 2-10% delithiation is investigated using Kα and Kβ fluorescence (spin sensitive) followed by K-edge XAFS for Cobalt and Oxygen. Figure 1

Optimizing electronic structure and surface morphology are of great importance to achieve highly active and stable electrocatalyst for hydrogen evolution reaction (HER). In this paper, the vertically aligned Cu doped Ni/Ni3S2 nanosheet was successfully deposited on Ti mesh (NiCux/Ni3S2/TM, x = Cu/Ni atomic ratio in NiCux) by facile electrodeposition method. Phase composition, surface morphology and electronic structure information were characterized by XRD, SEM, TEM and XPS. The results unraveled that Cu doping induced the changes in both electronic structure and surface morphology of Ni/Ni3S2 sample, which were in favor of promoting the breakage of H-O bond in H2O and optimizing Ni-Hads adsorption energy, thus improving HER activity with decreased overpotential at −10 mA/cm2 by 202 mV. The influence of Cu(NO3)2 precursor content on HER activity of as-prepared NiCux/Ni3S2/ TM was investigated. NiCu0.57/Ni3S2/TM prepared with 1.2 mM Cu(NO3)2 exhibited the highest electrocatalytic activity toward HER with overpotential of 239 mV at −10 mA/cm2 and Tafel slope of 86 mV/dec. The enhanced activity and superior stability for NiCu0.57/Ni3S2/TM were ascribed to the change in electronic structure and surface morphology.

Layered alkali transition metal oxides (i.e., LiMO2 and NaMO2, M=transition metal) are the premier class of cathode materials in lithium- and sodium-ion battery system. The safety characteristics of LiMO2 cathode based LIBs are one of the most critical barriers to be overcome for the large scale application such as EV. One of the main reasons that might cause safety hazards of the LIB is associated with the thermal instability of charged Li1-xMO2 cathode materials, which is related to the occurrence of exothermic reactions between flammable electrolyte and liberating oxygen from charged Li1-xMO2 at high temperature. Based on the structural homology between the layered LiMO2 and NaMO2, we expect that the investigation of thermal stability of charged Na1-xMO2cathode materials is also important for the practical use of SIBs. However, few attentions have been paid on safety issue of SIBs. In this study, the thermal stability of charged Na1-xMO2 cathode materials is investigated by using combined in situ time-resolved X-ray diffraction and mass spectroscopy (TR-XRD/MS), which allows simultaneous observation of the structural changes and gas species that are evolved during thermal decomposition of charged cathode materials, especially O2 gas in our interest. In addition, the ex situ/in situ X-ray absorption spectroscopy (XAS) has been also utilized to look at the local and electronic structural changes occurring during thermal decomposition in an elemental selective way. By utilizing combined X-ray techniques, we are able to get better understanding of structural and electronic structure changes in charged cathode materials during thermal decomposition. In this presentation, the thermal decomposition behavior of charged Na1-xMO2(M=Co, Cr) cathodes will be covered. Acknowledgement The work done at Brookhaven National Lab. was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. DOE under Contract No. DE-SC0012704.

A technique for estimating a plasma drift velocity distribution in the ionosphere is presented. This technique is based on a framework for representing a global vector field on a sphere by using a set of localized basis functions which is newly derived as a variant of the spherical elementary current system (SECS). A vector field on a sphere can be divided into its divergence-free (DF) component and curl-free (CF) component. The DF and CF components can then be represented by weighted sums of the DF and CF vector-valued basis functions, respectively. While the SECS basis functions have a singular point, the new basis functions do not diverge over a sphere. This property of the new basis function allows us to achieve robust prediction of the drift velocity at any point in the ionosphere. Assuming that the ionospheric plasma drift velocity has no divergence, its distribution can be represented by a weighted sum of the DF basis functions. The proposed technique estimates the ionospheric plasma drift velocity distribution from the SuperDARN data by using the DF basis functions. Since there are some wide gaps in the spatial coverage of the SuperDARN, an empirical convection model is combined with the framework based on the new basis functions. It is demonstrated that the proposed technique is useful for the estimation and modeling of the ionospheric plasma velocity distribution.

Unsteady mixed convective heat transfer flow past an inclined square cylinder is numerically investigated using a local multi-quadric radial basis function (MQRBF) interpolation. The blockage parameter (ratio of square cylinder length d to height of the computational domain H) varies from 0.025 to 0.2. Air is considered as the working fluid and Prandtl number is fixed at 0.71. Richardson number generally affects the heat transfer efficiency ranging from 0 to 20. Inclined angle of square cylinder ranges from 0° to 45°. The inlet flow is assumed to be laminar and uniform. At the outlet of the computational domain, a convective boundary condition is compared with a traditional Neumann condition. A study of the shape parameter of MQRBF which is sensitive to the distribution of inhomogeneous supporting nodes is provided. The representative streamlines, vortex structures and isotherm patterns are presented and discussed. In addition, the overall lift and drag coefficients, average Nusselt number and Strouhal number for unsteady flow are analyzed for various Reynolds number and Richardson number.

In this paper, adaptive meshfree methods using local nodes and radial basis functions (RBFs) which based on strong-form formulation is presented. In this present formulation, radial basis functions are used in the function approximation for the discretization of the governing system equations. Regularization techniques are suggested and examined to stabilize the solutions in order to obtain stable and accurate results. Different schemes for constructing regularization matrix are compared and discussed. As stability is restored, meshfree strong-form method using local nodes and RBFs can facilitate an easier implementation for adaptive analysis to achieve desired accuracy. Residual based error indicator is devised in the adaptive scheme. A simple and practical node refinement procedure is presented for node insertion at each adaptive step.

To avoid numerical inaccuracy of the transient solution by the time-domain solvers or frequency-domain solvers, a simultaneous extrapolation approach reconstructing of the wide-band frequency spectrum using low-frequency and early-time data by the local linear basis functions is presented. The basic idea is transforming the transient integral equations into the analytical-form matrix equation, which can be solved using basis functions with a local support. By means of the early-time and low-frequency data, the matrix equation is solved by the method of singular value decomposition to obtain the wide-band spectrum. The proposed approach is validated by several numerical examples and applied in calculating the transient horizontal electric field of a lightning channel. The major advantage of the presented approach is an efficient and stable algorithm that can be generalized to apply to other transient scenarios when frequency- and time-domain-based transient analysis are involved.

The local radial basis function (RBF) method is a promising solver for variable‐order time fractional diffusion equation (TFDE), as it overcomes the computational burden of the traditional global method. Application of the local RBF method is limited to Fickian diffusion, while real‐world diffusion is usually non‐Fickian in multiple dimensions. This article is the first to extend the application of the local RBF method to two‐dimensional, variable‐order, time fractional diffusion equation in complex shaped domains. One of the main advantages of the local RBF method is that only the nodes located in the subdomain, surrounding the local point, need to be considered when calculating the numerical solution at this point. This approach can perform well with large scale problems and can also mitigate otherwise ill‐conditioned problems. The proposed numerical approach is checked against two examples with curved boundaries and known analytical solutions. Shape parameter and subdomain node number are investigated for their influence on the accuracy of the local RBF solution. Furthermore, quantitative analysis, based on root‐mean‐square error, maximum absolute error, and maximum error of the partial derivative indicates that the local RBF method is accurate and effective in approximating the variable‐order TFDE in two‐dimensional irregular domains.

ABSTRACTA local radial basis function meshless (LRBFM) method is developed to solve coupled radiative and conductive heat transfer problems in multidimensional participating media, in which compact support radial basis functions (RBFs) augmented on a polynomial basis are employed to construct the trial function, and the radiative transfer equation (RTE) and energy conservation equation are discretized directly at nodes by the collocation method. LRBFM belongs to a class of truly meshless methods which require no mesh or grid, and can be readily implemented in a set of uniform or irregular node distributions with no node connectivity. Performances of the LRBFM is compared to numerical results reported in the literature via a variety of coupled radiative and conductive heat transfer problems in 1D and 2D geometries. It is demonstrated that the local radial basis function meshless method provides high accuracy and great efficiency to solve coupled radiative and conductive heat transfer problems in multidimensional participating media with uniform and irregular node distribution, especially for coupled heat transfer problems in irregular geometry with Cartesian coordinates. In addition, it is extremely simple to implement.

A novel upwind-based local radial basis function differential quadrature method for convection-dominated flows

Simulation of laminar backward facing step flow under magnetic field with explicit local radial basis function collocation method

Our work provides an effective feature based method for analyzing both steady state and short duration non-stationary power signal disturbances using a Local Linear Radial Basis Function Neural Network (LLRBFNN). In contrast to the normalized probabilistic neural network (PNN), the proposed LLRBFNN is an excellent approximation network, which performs the classification task with minimal amount of computational power than probabilistic neural network (PNN). The difference of the LLRBFNN with conventional Radial Basis Function Neural Network (RBFNN) is that a local linear model replaces the connection of weights between the hidden layer and output layer of conventional RBFNN. Both normalized time domain and frequency domain features are used for the training purpose. It is noticed that spectral entropy is an effective frequency domain feature for non-stationary power signal classification. Moreover the local linear model provides a robust model for network learning, which is not prone to local linear points. This is supported by the observation that both the LLRBFNN model and the global search optimization techniques like Genetic algorithm provide similar results.

Temporally local recurrent radial basis function network for modeling and adaptive control of nonlinear systems

Electronic band structure of ZrNCl and HfNCl

The observation of ultrafast and coherent control of spins in magnetic materials at room temperature [1-2] has prompted the experimental and theoretical efforts to understand the underlying mechanisms driving such magnetic phenomena. In order to understand the driving mechanisms, in this non-equilibrium regime, it is necessary to disentangle the relevant interactions (exchange, spin-lattice, electron-phonon, coulomb etc.).Stoichiometric B2 ordered epitaxial (001) FeRh undergoes a first order magnetic phase transition from antiferromagnetic (AFM) to ferromagnetic (FM) at ≈ 380K. In the AFM phase of FeRh, only Fe has net magnetic moment, whereas in the FM phase both Fe and Rh carry net moments. The phase transition is also accompanied by a ≈ 1% isotropic lattice expansion in the bulk BCC structure, and changes in electronic structure, see [3-5] and refs. therein. Since magnetic and structural dynamics can occur at different timescales, it makes FeRh an ideal candidate for disentangling relevant interaction mechanisms at different timescales. The phase transition has been extensively studied theoretically and experimentally [6-10], in thermal equilibrium (static heating) and at ultrafast time scales (fs- optical excitation), but a precise knowledge of the roles of the electronic, phononic and spin sub-systems remains elusive.We have studied the laser-driven AFM to FM phase transition in FeRh with X-ray absorption spectroscopy (tr-XAS) around the Fe L3 edge. The experiments were performed at the SCS Instrument of the European XFEL. We also performed the density functional theory (DFT) calculations to simulate the XAS spectra at different time delays including magnetic, lattice and temperature changes. Temperature modelling was done using two temperature model (2TM).In this contribution, we will discuss the changes in the electronic band structure of FeRh in the femto- and picosecond timescales, derived from the X-ray absorption spectroscopy measurements at the Fe L3 absorption and compare them with the density functional theory simulations. **