Single Point Charge Research Articles

BiLSTM‐based thunderstorm prediction for IoT applications

AbstractAlthough the market demand for smart devices (SDs) in the Internet of Things (IoT) era is surging, the corresponding thunderstorm protection measures have rarely attracted attention. This paper presents a thunderstorm prediction method with elevation correction, to reduce the thunderstorm damage to SDs by visually tracking thunderstorm activities. First, a self‐made three‐dimensional atmospheric electric field apparatus (3DAEFA) deployed in IoT is developed to collect real‐time AEF data. A 3DAEFA‐based localization model is established, and the localization formula after correction is derived. AEF data predicted by the bi‐directional long short‐term memory (BiLSTM) model are input to this formula to obtain thunderstorm point charge localization results. Then, the localization skill is evaluated. Finally, the proposed method is assessed in experiments, under single and multiple point charge conditions. There are significant reductions of at least 33.1% and 8.8% in ranging and elevation angle errors, respectively. Particularly, this post‐prediction correction reduces the deviation of fitted point charge moving paths by at most 0.189 km, demonstrating excellent application effects. Comparisons with radar charts and existing methods testify that this method can effectively predict thunderstorms.

An improved equipotential lab for parallel plates

The typical equipotential lab involves students sampling points in an electrode configuration: they move the probe around until they find a series of points with the same potential. Other authors have highlighted some difficulties with the traditional lab approach: most do not allow real-time visualization of equipotential lines, and students often seem to rely conceptually on single point charge equipotential models or Coulomb’s laws. I propose a different approach to the parallel plate lab: Students are directed to set up a grid of equally spaced points between parallel plates. Students measure and record probe voltages in a spreadsheet and analyze voltages as a function of x and y. I demonstrate typical results and briefly discuss possible extensions.

Novel way to construct spatially localized finite energy structures

In this work we introduce a procedure to find localized structures with finite energy. We start dealing with global monopoles, and add a new contribution to the potential of the scalar fields, to balance the contribution of the angular gradients of the fields which lead to a slow falloff in the energy density. Within the first order formalism, first order equations that are compatible with the equations of motion are obtained and the stability under small fluctuations is investigated. We then include another set of scalar fields and study how it contributes to change the profile of the localized structure. We also study how these configurations modify the electric properties of a system with a single point charge, with generalized electric permittivity controlled by scalar fields. In this new model, in particular, we show that, depending on the specific modification of the electric properties of the medium, the electric field may engender the unusual behavior of pointing towards a positive charge.

Molecular dynamics study of confined water in the periclase-brucite system under conditions of reaction-induced fracturing

The volume-increase associated with hydration reactions in rocks may lead to reaction-induced fracturing, but requires a stable water film to be present at reactive grain boundaries even when subject to compressive stress. Hydration of periclase to brucite is associated with a solid volume increase of ca. 110%. Recent experiments on the periclase-brucite system observed that when the effective mean stress exceeds 30 MPa, the reaction rate slows down dramatically. We hypothesize that for the brucite forming reaction to progress, the fluid film between grains must remain stable. If the applied pressure becomes larger than the hydration force, the fluid film will collapse and be squeezed out of the grain contacts. To quantify this effect, we study the behavior of a water film confined between periclase or brucite surfaces subject to compressive stress, by performing molecular dynamics simulations. The simulations are carried out using the ClayFF force field and the single point charge (SPC) water model in the molecular dynamics simulations program LAMMPS. The setup consists of two interfaces of either periclase or brucite surrounded by water. Our simulations show that when the pressure reaches a few tens of MPa, the water film collapses and reduces the water film to one or two water layers, while the self-diffusion coefficient of water molecules by a factor of eight. A water film thickness below two water layers is thinner than the size of the hydration shell around Mg2+-ions, which will limit ion-transport. The observed collapse of the water film to a single layer at a normal pressure of 25–30 MPa might explain the observed slow-down of reaction-induced fracturing in the periclase-brucite system.

Integral Representation of Electrostatic Interactions inside a Lipid Membrane.

Interactions between charges and dipoles inside a lipid membrane are partially screened. The screening arises both from the polarization of water and from the structure of the electric double layer formed by the salt ions outside the membrane. Assuming that the membrane can be represented as a dielectric slab of low dielectric constant sandwiched by an aqueous solution containing mobile ions, a theoretical model is developed to quantify the strength of electrostatic interactions inside a lipid membrane that is valid in the linear limit of Poisson-Boltzmann theory. We determine the electrostatic potential produced by a single point charge that resides inside the slab and from that calculate charge-charge and dipole-dipole interactions as a function of separation. Our approach yields integral representations for these interactions that can easily be evaluated numerically for any choice of parameters and be further simplified in limiting cases.

Extension of the DG Model to the Second-Order Quantum Correction for Analysis of the Single-Charge Effect in Sub-10-nm MOS Devices

We extended the density-gradient (DG) model to include a second-order quantum correction (SOQC) term. The DG model has been widely used as a device simulation model capable of simulating quantum effects in efficient way. However, when only the first order quantum correction term is considered in the DG model, it is difficult to accurately describe device characteristics such as carrier density or potential fluctuation in the narrow region due to discrete charges such as dopants and interface traps. Thus, we extended the DG model to the SOQC, implemented it as a three-dimensional (3D) simulator, and compared the simulation results for sub-10-nm devices, which have a single point charge, in the DG model and the 3D Schrodinger-Poisson (SP) solver. Through this, we identified that the DG extended to SOQC well reproduces the SP simulation results in terms of both capacitance-voltage (C-V) and local fluctuation in electron density.

Modeling of a charged dielectric interface: Comparison of the continuum and discrete lattice representations of surface charges

Two main approaches in particle-based simulations for modeling a charged surface are using explicit, discrete charges and continuum, uniform charges. It is well-known that these two approaches could lead to substantially distinct ionic distributions, whereas a systematic exploration of the origin is still absent. In this short communication, we calculate the electrostatic force of a single point charge above a planar substrate characterized by a surface charge density and dielectric mismatch and compare the differences in the electrostatic forces produced by discrete and continuum representations of surface charges. We demonstrate that while the model of uniform surface charges gives a rather simple picture, the model of discrete surface charges can exhibit different scenarios, depending on the respective values of ion-surface distance versus lattice spacing and a self-image interaction parameter.

Spatial averaging of electrostatic potential differences in layered nanostructures with ionic hopping conductivity

Laws of spatial averaging on nanoscale for local electrostatic potential differences in ionic conductors are of key importance for the understanding of ion-transport phenomena and effects in space-charge layers. Currently, these laws are not investigated. As a consequence, the leading software packages for nanoscience do not have any competence for modeling of space-charge formation/relaxation in nanostructures with ionic hopping conductivity. So the article addresses the theme. For a layered nanostructure {Xk}, formed by parallel crystallographic Xk planes, an average electrostatic potential difference (<Vk,k+1>) in a non-uniform field is defined in terms of normalized sums Σ of the local works Wk,k+1 for Xk→Xk+1 transitions of mobile ions in a field of a single point charge. At a weak external electrical influence on {Xk}, the <Vk,k+1> can be easily generalized for a non-uniform field created by a set of point charges. The sums ΣWk,k+1 are calculated for small average distances (~0.6 nm) between mobile ions (as in advanced superionic conductors). Computer experiments show: (i) ΣWk,k+1 sums are independent of k-indices with the accuracy ~10%, (ii) probability density functions for local potential differences Vk,k+1 are close to normal distributions and (iii) <Vk,k+1> ≈ VUk,k+1, where VUk,k+1 is a potential difference in a uniform electrostatic field. These nanoscale laws allow manipulating by an average potential difference (<Vk,k+N>) between Xk and Xk+N planes (N > 1), so the modeling of non-stationary ion-transport processes and energy flows in parallel combinations of nanostructures become possible.

Interplay between Polarizability and Hydrogen Bond Network of Water: Reparametrizing the Flexible Single-Point-Charge Water Model by the Nonlinear Adaptive Force Matching Approach.

An adaptive force matching (AFM) scheme using the nonlinear optimization to reparametrize the three-site, flexible, and polarizable single-point-charge (SPC) water model is reported. We compare the radial distribution functions of the intermolecular oxygen-oxygen, oxygen-hydrogen, and hydrogen-hydrogen distances with the recent scattering experiments, the previous AFM-fitting water model (MP2f), and the atomic multipole expanded AMOEBA model. Our nonpolarizable SPC-3f(0) model captures the feature of the first solvation shell of bulk water. With the ad hoc inclusion of the isotropic polarizability, the polarizable SPC-3f(0.6) water model recovers the many-body effect of the second solvation shell. In the n-body decomposition analysis, the SPC-3f(0) model predicts the best agreement with MP2/aug-cc-pVTZ calculations with the use of the low-dimensional (H2O)4-ring and (H2O)6-ring clusters. For the comparison using the three-dimensional (H2O)6-prism and (H2O)16-4444a clusters, SPC-3f(0.6) predicts the results consistent with those of AMOEBA and MP2 levels. For simulating a water-cluster-dominant system such as supercritical water, SPC-3f(0) well characterizes the combination mode of bending and stretching at 5300 cm-1.

Emission spectrum of sprites caused by the quasi-electrostatic field above thunderstorm clouds

The synthetic spectrum of sprites caused by quasi-electrostatic field (QEF) of thunderstorm clouds is studied and calculated based on the Boltzmann equation and a single-point charge model. The reduced E-field determined with the single-point charge model is inputted to the Boltzmann model, and the electron energy distribution in the weakly ionization gas in the presence of the QEF is obtained. On the basis of these calculations, the excitation rate of the emission bands of sprites is calculated. The simulation results show that the volume emission rate of each emission band increases with the increase of the reduced E-field. The emission almost comes from several neutral N2 molecule emission bands, while the reduced E-field is lower. With the increase of the reduced E-field, the volume emission rate from two bands of $${\text{N}}_{2}^{ + }$$ ion gradually increases, and the magnitude of volume emission rate from $${\text{N}}_{2}^{ + }$$ ion-emission bands equals or even exceeds that of the neutral N2 molecule emission bands. The absolute values of volume emission at both N2 molecule and $${\text{N}}_{2}^{ + }$$ ion-emission bands can be obtained based on the single-point charge model and the Boltzmann model. The calculated brightness can reach dozens of million Rayleighs which is consistent with the observation.

On the Alternative Vector Potential Formulation of the Sommerfeld Half-Space Problem

We address the non-uniqueness of the vector potential for the Sommerfeld half-space problem with a horizontal Hertzian dipole. In contrast to the classical solution, which utilizes horizontal and vertical components of the vector potential, the formulation presented here employs two horizontal components. In this approach, unlike in the traditional one, the scalar potentials of single-point charges associated with the vertical and horizontal Hertzian dipoles are identical.

Experimental investigation of the influence of spatially distributed charges on the inertial mass of moving electrons as predicted by Weber’s electrodynamics

It was shown (J. Phys. Soc. Jpn. 62, 1418 (1993)) that Weber’s force law predicts an influence upon the apparent inertial mass of electrically charged particles in relative motion. The quantity of this influence, called Weber’s mass, depends on the relative motion (both speed and acceleration) and the relative spatial distribution of the particles. A special case was analytically solved, in which the motion of a single point charge was considered, surrounded by a static and fixed spherical surface with a homogeneous charge distribution. The first experimental test of the prediction showed positive results (Annal. Fond. Louis de Broglie, 24, 161 (1999)). Two reproductions were carried out, in which null results were reported together with an explanation for the previous positive result. It was suggested that a possible reason for the null result in the experimental setup could be that the charges could freely move on the surface. We set out to reproduce all previous experiments to get detailed insight into the problem, after which we designed a setup that would exclude the possibility of the moving charges on the surface. In all situations we could confirm the null results with a statistical precision of up to 0.009%

Polarization, donor-acceptor interactions, and covalent contributions in weak interactions: a clarification.

The concepts of polarization (induction), charge transfer and covalent bonding contributions are discussed in terms of weak interactions. They are shown to be different incarnations of the same phenomenon, so that using polarization to describe them is most consistent as it is the only real, measurable and uniquely defined quantity of the three. Dispersion is discussed as a form of polarization within the Feynman description. Model calculations are described. Graphical abstract The electron density of a hydride ion (nucleus white) polarized by a single positive point charge (brown).

About improving efficiency of the [formula omitted] algorithms when computing the inter-particle forces in beam dynamics

In the paper, a problem of improving efficiency of the particle–particle– particle-mesh (P3M) algorithm in computing the inter-particle electrostatic forces is considered. The particle-mesh (PM) part of the algorithm is modified in such a way that the space field equation is solved by the direct method of summation of potentials over the ensemble of particles lying not too close to a reference particle. For this purpose, a specific matrix “pattern” is introduced to describe the spatial field distribution of a single point charge, so the “pattern” contains pre-calculated potential values. This approach allows to reduce a set of arithmetic operations performed at the innermost of nested loops down to an addition and assignment operators and, therefore, to decrease the running time substantially. The simulation model developed in C++ substantiates this view, showing the descent accuracy acceptable in particle beam calculations together with the improved speed performance.

Dipole Moment of a Charged Particle Trapped at the Air-Water Interface.

The interaction between two charged particles (such as nanoparticles or colloids) trapped at the air-water interface becomes dipolar at large separations. The corresponding dipole moment can be modeled by considering a single point charge located exactly at the interface, but this model fails to correctly predict the dipole moment's dependence on the salt concentration in the aqueous medium. We extend the single point charge model to two point charges that are separated by a fixed distance and are located at the air-water interface, with one charge being immersed in air and the other in the solvent. The two point charges represent the surface charges at the air-exposed and water-exposed regions of an interface-trapped particle. The two point charges also account for the spatial extension of the particle. On the basis of the Debye-Hückel model, we derive mathematical expressions for the interaction between two pairs of charges and discuss the salt concentration dependence of the dipolar moment at large separations. Our results reveal a residual dipole moment in the limit of large salt content that originates from the charge attached to the air-exposed region of the particle. We discuss nonlinear screening effects and compare the predicted dipolar moments with recent experimental results.

Discovery of novel human epidermal growth factor Receptor-2 inhibitors by structure-based virtual screening

Background:Human epidermal growth factor receptor-2 (HER2) is a trans-membrane receptor like protein, and aberrant signaling of HER2 is implicated in many human cancers, such as ovarian cancer, gastric cancer, and prostate cancer, most notably breast cancer. Moreover, it has been in the spotlight in the recent years as a promising new target for therapy of breast cancer.Objective:Since virtual screening has become an integral part of the drug discovery process, it is of great significant to identify novel HER2 inhibitors by structure-based virtual screening.Materials and Methods:In this study, we carried out a series of elegant bioinformatics approaches, such as virtual screening and molecular dynamics (MD) simulations to identify HER2 inhibitors from Food and Drug Administration-approved small molecule drug as potential “new use” drugs. Results: Molecular docking identified top 10 potential drugs which showed spectrum affinity to HER2. Moreover, MD simulations suggested that ZINC08214629 (Nonoxynol-9) and ZINC03830276 (Benzonatate) might exert potential inhibitory effects against HER2-targeted anti-breast cancer therapeutics.Conclusion:Together, our findings may provide successful application of virtual screening studies in the lead discovery process, and suggest that our discovered small molecules could be effective HER2 inhibitor candidates for further study.SUMMARY A series of elegant bioinformatics approaches, including virtual screening and molecular dynamics (MD) simulations were took advantage to identify human epidermal growth factor receptor-2 (HER2) inhibitors. Molecular docking recognized top 10 candidate compounds, which showed spectrum affinity to HER2. Further, MD simulations suggested that ZINC08214629 (Nonoxynol-9) and ZINC03830276 (Benzonatate) in candidate compounds were identified as potential “new use” drugs against HER2-targeted anti-breast cancer therapeutics. Abbreviations used: HER2: Human epidermal growth factor receptor-2, FDA: Food and Drug Administration, PDB: Protein Database Bank, RMSDs: Root mean square deviations, SPC: Single point charge, PME: Particle mesh Ewald, NVT: Constant volume, NPT: Constant pressure, RMSF: Root-mean-square fluctuation.

Ab Initio Liquid Water Dynamics in Aqueous TMAO Solution.

Ab initio molecular dynamics (AIMD) simulations in trimethylamine N-oxide (TMAO)-D2O solution are employed to elucidate the effects of TMAO on the reorientational dynamics of D2O molecules. By decomposing the O-D groups of the D2O molecules into specific subensembles, we reveal that water reorientational dynamics are retarded considerably in the vicinity of the hydrophilic TMAO oxygen (O(TMAO)) atom, due to the O-D···O(TMAO) hydrogen-bond. We find that this reorientational motion is governed by two distinct mechanisms: The O-D group rotates (1) after breaking the O-D···O(TMAO) hydrogen-bond, or (2) together with the TMAO molecule while keeping this hydrogen-bond intact. While the orientational slow-down is prominent in the AIMD simulation, simulations based on force field models exhibit much faster dynamics. The simulated angle-resolved radial distribution functions illustrate that the O-D···O(TMAO) hydrogen-bond has a strong directionality through the sp(3) orbital configuration in the AIMD simulation, and this directionality is not properly accounted for in the force field simulation. These results imply that care must be taken when modeling negatively charged oxygen atoms as single point charges; force field models may not adequately describe the hydration configuration and dynamics.

Insights into Kelvin probe force microscopy data of insulator-supported molecules

We present a detailed analysis and understanding of Kelvin probe force microscopy (KPFM) data for a system of point charges in a vacuum-dielectric tip-sample system. Explicit formulae describing the KPFM signal $\ensuremath{\Delta}V$ are derived for the two KPFM operation modes, namely amplitude modulation and frequency modulation (FM). The formulae allow for a physical interpretation of the resulting KPFM signal, reveal contributing parameters, and especially disclose an additive behavior. We numerically evaluate these equations and show exemplary KPFM slice data for a single point charge. The theoretical analysis is complemented by two-dimensional FM-KPFM maps obtained experimentally on 2,5-dihydrobenzoic acid on calcite $(1\phantom{\rule{0.59998pt}{0ex}}0\phantom{\rule{0.59998pt}{0ex}}.\phantom{\rule{0.59998pt}{0ex}}4)$. The molecules assemble in two coexisting phases understood as protonated and deprotonated molecules. The two-dimensional maps reveal a convex shape of the KPFM signal $\ensuremath{\Delta}V$ across the islands and a clear difference between the two phases is revealed. Furthermore, we apply the theoretically suggested difference strategy to extract the molecular component from the measured total KPFM signal.

Polarizability effects in molecular dynamics simulations of the graphene-water interface

The importance of including the polarizability of both water and graphene in molecular dynamics simulations of the water/graphene system was quantified. A thin film of either rigid single point charge extended (SPC/E) water or polarizable simple 4-site water model with Drude polarizability (SWM4_DP) water on non-polarizable and polarizable graphene surfaces was simulated. The graphene surface was either maintained neutral or charged, positively and negatively. The results suggest that SPC∕E and SWM4_DP water models yield very similar predictions for the water structural properties on neutral non-polarizable graphene, although they yield slightly different dynamical properties of interfacial water on neutral non-polarizable graphene. More pronounced were the differences obtained when graphene was modeled with a polarizable force field. In particular, the polarizability of graphene was found to enhance the number of interfacial SWM4_DP water molecules pointing one of their OH bonds towards the neutral surface. Despite this structural difference, the dynamical properties predicted for the interfacial SWM4_DP water were found to be independent on polarizability as long as the polarizability of a carbon atom is smaller than α = 0.878 A. On charged graphene surfaces, the effect of polarizability of graphene on structural properties and some dynamical properties of SWM4_DP water is negligible because electrostatic forces due to surface charge dominate polarization forces, as expected. For all cases, our results suggest that the hydrogen bond network is insensitive to the polarizability of both water and graphene. Understanding how these effects will determine the accumulation of ions near neutral or charged graphene could have important implications for applications in the fields of energy storage and water desalination.

Fluctuations and micro-heterogeneity in aqueous mixtures

The problem as to why water-water density correlations are systematically overestimated in computer simulation of aqueous mixtures is examined through an extensive molecular dynamics study of mixtures of the extended single point charge water model with a fully miscible weaker version of it, obtained by scaling down the site partial charges by a factor 2/3, thereby eliminating solute-solvent size differences. The study reveals that enhanced water correlations is a genuine physical effect, and are not an artifact of the simulations or the models, as previously suggested in the context of realistic aqueous mixtures. Rather, they correspond to the existence of strongly correlated water domains, for "weak-water" mole fraction x > 0.4, that modulate the spatial decay of the density correlations. These domains produce a prepeak in the structure factor, suggesting that simple aqueous mixture might behave just like micro-emulsions. The overestimated long range water correlations result from incorrect predictions of the asymptote of these correlations, which themselves arise from size limitations of the simulation box. However, by requiring consistency between thermodynamical and structural expressions of the concentration fluctuations, a method to predict the proper decay of the correlation function is obtained herein, inspired by the formal analogy with micro-emulsions. This study provides a new insight for the large values of the experimental Kirkwood-Buff integrals for many aqueous mixtures: these mixtures are in a Lifshitz-type regime, where concentration fluctuations compete with water domain formation.