Charge Variation Research Articles

Protein network centralities as descriptor for QM region construction in QM/MM simulations of enzymes.

The construction of a suitable QM region is the most crucial step in setting up hybrid quantum mechanics/molecular mechanics (QM/MM) simulations for enzymatic reactions. The QM region should ideally include all important amino acids residues, while being as small as possible to save computational effort. Most available methods for systematic QM region construction are based either on the distance of single amino acids to the active site or on their electrostatic effect. Such approaches might miss non-electrostatic and long-range allosteric interactions. Here, we present a proof of concept study for the application of protein network analysis to tackle this problem. Specifically, we explore the use of the protein network centralities as descriptor for QM region construction. We find that protein network centralities, in particular the betweenness centrality, can be a useful descriptor for systematic QM region construction. We show that in combination with our previously developed point charge variation analysis, they can be used to identify important residues that are missed in purely electrostatic approaches.

The effect of electrically pre-stressing of high DC electric field on performance of SDBD thruster in near space

The space charge on the surface of solid dielectric has great influence on the surface dielectric barrier discharge (SDBD). In this paper, the surface space charge of SDBD is effectively regulated by the effect of electrically pre-stressing of high DC electric field to improve the dynamic performance of ion wind thruster. The conduction current, surface charges, thrust and thrust-to-power ratio are measured respectively for the ion wind thruster with and without the effect of electrically pre-stressing. The experimental results show that compared with the ion wind thruster without the effect of electrically pre-stressing, the instantaneous polarization current of the SDBD ion wind thruster with the effect of electrically pre-stressing is reduced by 42.7%, and the attenuation constant of the relaxation polarization current is reduced by about 28.8%, which effectively reduces the relaxation polarization loss of the thruster under the alternating electric field. In addition, the discharge time of anode and cathode increases respectively by about 20.0% and 43.3%, and the variation of surface space charge increases by about 50.6% in one voltage cycle. The saturation thrust of the thruster is increased from 1070 μN/m to 1660 μN/m by about 55.1%. The maximum thrust-to-power ratio of the thruster is increased from 993 μN/kW to 2125 μN/kW by about 114.0%.

Evolution of the Fe-Co magnetism and magnetic proximity effects in alternate Fe/Co monolayers on nonmagnetic Cu3Au(001)

Magnetic heterostructures with ferromagnetic/nonmagmetic interfaces are very interesting materials due to the possibility to switch the magnetization, to control the induced magnetic moment, and also due to interfacial effects. The tuning of the spin-orbit coupling in magnetic materials allows engineering new spintronic devices. Using density functional theory, the induced local magnetic moments in copper and gold surface atoms of ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ due to the deposited alternate magnetic Fe and Co monolayers were studied. To observe the tuning mechanism, the spin density of the $\mathrm{FeCo}/{\mathrm{Cu}}_{3}\mathrm{Au}(001)$ as a function of the number of deposited magnetic monolayers was extensively investigated. The Fe/Co deposition induces a hybridization between electronic states of the magnetic and nonmagnetic interface atoms, generating a broadening in $d$ bands of the deposited material, engineering the magnetic moments of the interface atoms. This observed hybridization elucidates the charge variation in the interface atoms for stacking sequences starting with Fe or with Co as the first magnetic layer in direct contact with the ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ substrate. By performing the spin-charge density calculations, we demonstrated that this magnetic induction occurs only for the nonmagnetic Cu-Au atoms at the ${\mathrm{Cu}}_{3}\mathrm{Au}(001)$ surface.

Mechanical tuning of virus-like particles

HypothesisVirus-like particles (VLPs) are promising scaffolds for developing mucosal vaccines. For their optimal performance, in addition to design parameters from an immunological perspective, biophysical properties may need to be considered. ExperimentsWe investigated the mechanical properties of VLPs scaffolded on the coat protein of Acinetobacter phage AP205 using atomic force microscopy and small angle X-ray scattering. FindingsInvestigations showed that AP205 VLP is a tough nanoshell of stiffness 93 ± 23 pN/nm and elastic modulus 0.11 GPa. However, its mechanical properties are modulated by attaching muco-inert polyethylene glycol to 46 ± 10 pN/nm and 0.05 GPa. Addition of antigenic peptides derived from SARS-CoV2 spike protein by genetic fusion increased the stiffness to 146 ± 54 pN/nm although the elastic modulus remained unchanged. These results, which are interpreted in terms of shell thickness and coat protein net charge variations, demonstrate that surface conjugation can induce appreciable changes in the biophysical properties of VLP-scaffolded vaccines.

Quantum dot photoluminescence as charge probe for plasma exposed surfaces

Quantum dots (QDs) are used as nanometer-sized in situ charge probes for surfaces exposed to plasma. Excess charges residing on an electrically floating surface immersed in a low-pressure argon plasma are detected and investigated by analysis of variations in the photoluminescence spectrum of laser-excited QDs that were deposited on that surface. The experimentally demonstrated redshift of the PL spectrum peak is linked to electric fields associated with charges near the QDs’ surfaces, a phenomenon entitled the quantum-confined Stark effect. Variations in the surface charge as a function of plasma input power result in different values of the redshift of the peak position of the PL spectrum. The values of redshift are detected as 0.022 nm and 0.073 for 10 and 90 W plasma input powers, respectively; therefore indicating an increasing trend. From that, a higher microscopic electric field, V m−1 for 90 W compared to V m−1 for 10 W input power, which is coupled to an increased electric field in the plasma sheath, is sensed by the QDs when plasma input power is increased.

Critical parameters controlling wettability in hydrogen underground storage - An analytical study

The large-scale implementation of hydrogen economy requires immense storage spaces to facilitate the periodic storage/production cycles. Extensive modelling of hydrogen transport in porous media is required to comprehend the hydrogen-induced complexities prior to storage to avoid energy loss. Wettability of hydrogen-brine-rock systems influence flow properties (e.g. capillary pressure and relative permeability curves) and the residual saturations, which are all essential for subsurface hydrogen systems. This study aims to understand which parameters critically control the contact angle for hydrogen-brine-rock systems using the surface force analysis following the DLVO theory and sensitivity analysis. Furthermore, the effect of roughness is studied using the Cassie-Baxter model. Our results reveal no considerable difference between H 2 and other gases such as N 2 . Besides, the inclusion of roughness highly affects the observed apparent contact angles, and even lead to water-repelling features. It was observed that contact angle does not vary significantly with variations of surface charge and density at high salinity, which is representative for reservoir conditions. Based on the analysis, it is speculated that the influence of roughness on contact angle becomes significant at low water saturation (i.e. high capillary pressure).

Unraveling photo-induced proton transfer mechanism and proposing solvent regulation manner for the two intramolecular proton-transfer-site BH-BA fluorophore

To expound specific excited state processes of the novel excitation wavelength dependent emission BH-BA fluorophore for better subsequent applications, this wok mainly focus on exploring photo-induced hydrogen bonding geometrical changes, excited state intramolecular proton transfer (ESIPT) mechanism and related regulated behavior via solvent polarity. The differences of structural parameters, infrared (IR) vibrational spectra, core-valence bifurcation (CVB) index as well as electronic densities ρ(r) between S0 and S1 states related to dual hydrogen bonds (O1-H2···N3 and O4-H5···N6) reveal S1-state hydrogen bonding strength facilitate ESIPT behaviors for BH-BA system. Of particular note, O4-H5···N6 plays a more dominant role. Photo-induced intramolecular charge transfer (ICT) and variations of Hirshfled and NPA charges over atoms related to hydrogen bonding moieties promote the ESIPT tendency for BH-BA. Combined potential energy surfaces (PESs), transition state (TS) and intrinsic reaction coordinate (IRC) paths, we illustrate the excited state intramolecular single proton transfer (ESISPT) mechanism of BH-BA should occur along with O4-H5···N6 hydrogen bonding wire, which could be adjusted by surrounding solvent polarity.

Real-Space Charge Density Profiling of Electrode-Electrolyte Interfaces with Angstrom Depth Resolution.

The accumulation and depletion of charges at electrode-electrolyte interfaces is crucial for all types of electrochemical processes. However, the spatial profile of such interfacial charges remains largely elusive. Here we develop charge profiling three-dimensional (3D) atomic force microscopy (CP-3D-AFM) to experimentally quantify the real-space charge distribution of the electrode surface and electric double layers (EDLs) with angstrom depth resolution. We first measure the 3D force maps at different electrode potentials using our recently developed electrochemical 3D-AFM. Through statistical analysis, peak deconvolution, and electrostatic calculations, we derive the depth profile of the local charge density. We perform such charge profiling for two types of emergent electrolytes, ionic liquids, and highly concentrated aqueous solutions, observe pronounced sub-nanometer charge variations, and find the integrated charge densities to agree with those derived from macroscopic electrochemical measurements.

Air shower radio signal electric field orientation as measured with the Astroneu Cosmic Ray telescope.

The Astroneu cosmic ray telescope is a small scale hybrid array consisting of both scintillator counters and electromagnetic radiation detectors in the radio-wave frequency (RF) band (antennas). Astroneu was installed and operated in the area of the Hellenic Open University (HOU) campus near the city of Patras in Greece. In the present development phase, the Astroneu telescope includes two stations consisting of 3 scintillation detectors modules (SDM) and one RF antenna while a third station includes 3 particle detectors and 4 RF antennas (3SDM-4RF). In this context we present the resent results from both the 3SDM-4RF autonomous station and simulations related to the estimation of the direction of the electric field emitted during the air shower development. The electric field measured in the ground level is the superposition of the two dominant emission mechanism, the time depended transverse current induced by the geomagnetic field and the net negative charge variation at the shower front. Since the electric field emitted by the two contributions is polarized in different directions the measured electric field in the ground encloses information about the charge-excess to geomagnetic ratio (CGR). Furthermore the orientation of the electric field emitted by charge-excess mechanism is strongly depends from the distance to the shower core (the intersection of the shower axis with the ground level). In this study we use the core information as reconstructed using the radio data and simulations. The estimated charge-excess to geomagnetic ratio is in agreement with previous studies which reveals that the shower core reconstruction method is efficient. Finally we report on that CGR measurements can be used for an efficient noise rejection in a future self trigger mode

Online Battery SOH Prediction under Intra-Cycle Variation of Discharge Current and Non-Standard Charging and Discharging Practices

Online SOH prediction of a battery is essential for battery management in real-world applications. Although many approaches have been proposed to date, most conventional approaches to SOH prediction neither incorporate intra-cycle variation of discharge currents nor consider non-standard charging and discharging practices along cycles. For real-world applicability, the above two factors, varying discharge current and non-standard practices, are crucial to deal with. This paper presents an approach to online SOH prediction based on charging and discharging cycles under intra-cycle variation of discharge current and non-standard charging and discharging practices. Here, for online SOH prediction, we represent a cyclic history of terminal voltages and currents by a vector sequence formed by four indices: total charge, voltage-time entropy, average and variance of current, where average and variance of current are intended to deal with varying discharge current. Furthermore, we identify various minimum ranges of charging and discharging voltages that can provide accurate relation between four indices and SOH under non-standard practices, while transforming this relation into that of standard practices. For experiments, an LSTM stack is implemented for the proposed online SOH prediction. The results indicate that the proposed approach is capable of accurate online SOH prediction even under randomly varying discharging currents and non-standard practices with RMSE errors of about 0.5% as well as of about 95%.

Relative energies without electronic perturbations via alchemical integral transform.

We show that the energy of a perturbed system can be fully recovered from the unperturbed system's electron density. We derive an alchemical integral transform by parametrizing space in terms of transmutations, the chain rule, and integration by parts. Within the radius of convergence, the zeroth order yields the energy expansion at all orders, restricting the textbook statement by Wigner that the p-th order wave function derivative is necessary to describe the (2p + 1)-th energy derivative. Without the need for derivatives of the electron density, this allows us to cover entire chemical neighborhoods from just one quantum calculation instead of single systems one by one. Numerical evidence presented indicates that predictive accuracy is achieved in the range of mHa for the harmonic oscillator or the Morse potential and in the range of machine accuracy for hydrogen-like atoms. Considering isoelectronic nuclear charge variations by one proton in all multi-electron atoms from He to Ne, alchemical integral transform based estimates of the relative energy deviate by only few mHa from corresponding Hartree-Fock reference numbers.

Influence of needle electrode arrangement on gas transportation performance of the multi-needle ionic wind pump

The ionic wind pump with multi-electrode arrangement is helpful in enlarging its application. However, the arrangement has an inherent mutual interference among the electrodes during discharging process, which have a vital influence on the transportation performance of the ionic wind pump. Meanwhile, the relevance between the mutual interference and the intensity of the ionic wind has not been clearly revealed. In this study, the gas transportation experiments of the multi-needle electrode ionic wind pump are conducted. The intensity variation of the ionic wind with mutual interference is observed in the experiments. A simulation model based on the plasma transportation is proposed to describe the multi-needle discharging process with mutual interference effect. The EHD force is used as the indicator parameter for the intensity of the ionic wind. The experimental results show that the measured mass flow rate of the ionic wind pump is enhanced under dual-row needles and weakened under triple-row needles. Based on the simulation results, the above phenomenon is attributed to variations of the space charge and electric field induced by multi-needle discharging. The added needle electrodes reduce the electric field intensity per needle while increasing the net negative charge in the space. Due to the discharging interference among the needles, the increment of the net negative charge is not proportional to the number of needles. As a result, comparing the three arrangements from the simulations, the electrohydrodynamic (EHD) force of each needle, which is the electric field intensity multiplying by space charge density, increases approximately 45.8% under dual needles and decreases approximately 38.1% under triple needles. The conclusions obtained in this paper can help to guide the design and optimization of the multi-needle ionic wind pump.

Carrier-envelope phase controlled dynamics of relativistic electron beams in a laser-wakefield accelerator

In laser-wakefield acceleration, an ultra-intense laser pulse is focused into an underdense plasma in order to accelerate electrons to relativistic velocities. In most cases, the pulses consist of multiple optical cycles and the interaction is well described in the framework of the ponderomotive force where only the envelope of the laser has to be considered. But when using single-cycle pulses, the ponderomotive approximation breaks down, and the actual waveform of the laser has to be taken into account. In this paper, we use near-single cycle laser pulses to drive a laser-wakefield accelerator. We observe variations of the electron beam pointing on the order of 10 mrad in the polarisation direction, as well as 30% variations of the beam charge, locked to the value of the controlled laser carrier-envelope phase, in both nitrogen and helium plasma. Those findings are explained through particle-in-cell simulations indicating that low-emittance, ultra-short electron bunches are periodically injected off-axis by the transversally oscillating bubble associated with the slipping carrier-envelope phase.

A drain extended FinFET with enhanced DC/RF performance for high-voltage RF applications

A drain-extended fin field-effect transistor (FinFET) with a dual material gate (DMG) and a high-k field plate (FP), named DF-DeFF, is proposed for high-voltage radio frequency (RF) applications. The FP induces the charge variation in the drain extension, which appears as either the extended depletion in the gate-off state or the electron accumulation in the gate-on state. Along with the FP, the DMG forms a step-like potential variation along the channel, which leads to electron acceleration and the screening effect on the drain-to-source voltage (V DS). These effects give significant advantages to the DC characteristics, including breakdown voltage (V BD) and on-resistance (R on), and the RF characteristics, including transconductance (g m) and output-resistance (r o). Compared to the latest high-voltage RF FinFETs, the DF-DeFF shows a drastic improvement in the major performance indicators such as V BD, cut-off frequency (f T), and maximum oscillation frequency (f MAX). These results indicate that DF-DeFF is a FinFET with sufficient competitiveness even in high voltage circumstances.

Stability and formation process of hydrogen-bonded organic porous thin films: A molecular dynamics study

Molecular dynamics simulation using the reactive force field was performed to investigate the stability and formation mechanisms of organic porous thin films made of 1,3,5-tris(4-carboxyphenyl) benzene (BTB) molecules fabricated at the air/water interface. A single-layer honeycomb structure is found to be unstable, whereas thicker films are stable, which is consistent with experimental findings. The slight corrugation of the existing film produces local charge variation that attracts isolated molecules via the Coulomb interaction. When the isolated molecule approaches the film, a hydrogen bond is formed, and then the molecule adjusts the adsorption configuration by itself to maximize both horizontal and vertical intermolecular interactions. The key to the initial hydrogen bond formation is suggested to be the density of the molecules provided in the system as well as the spontaneous alignment of the BTB molecules to the solution/water interface. Our study showed that the BTB film is stable, and the molecules are self-assembled without external forces in the quasi-two-dimensional system. These results suggest that the dominant factor for the film formation at the air/water interface is interactions among BTB molecules and confinement to the two-dimensional space.

Variation of Electrical Resistivity and Charge Passed in High-Performance Concrete

This study investigated the variation of bulk resistivity (BR) and charge passed for various high-performance concrete (HPC) mixtures based on significant factors (i.e., geometric size, operation frequency, and mixture constituents and proportions) using three testing instruments. These instruments were a surface resistivity (SR) meter and two bulk conductivity meters: one for using the BR data at a constant frequency, and the other at a wide range of frequencies. These HPC mixtures were categorized into several groups based on various supplementary cementitious materials (SCMs). The variation and distribution of BR and the charge passed were investigated and statistical analysis results showed that the addition of SCMs and their varying replacement level remarkably influenced the reduction of charge passed in each group over an extended period. The results revealed that, for fly ash-based ternary mixtures, the addition of 3% metakaolin or 12% silica fume resulted in the highest reduction of charge passed over time (82% and 90%, respectively). For cost purposes, 5% silica fume replacement in ternary mixtures was chosen as an optimal solution. Finally, this study offered promising options for charge passed computation to assess corrosion in light of simple, rapid, and reliable SR/BR measurement.

Interaction of surfactants with phospholipid vesicles in the low concentration regime

The interactions between diluted phospholipid vesicles (0.3 μM - 40 μM) and surfactants (around their cmc) have been investigated as model of the phenomena taking place when enveloped viruses are challenged by detergent formulations such as mouthwashes or dishwashing liquids. We have used negatively charged Small Unilamellar Vesicles (SUVs) to simulate the negatively charged viral envelope and surfactants with different charges: the anionic Sodium Dodecyl Sulphate (SDS), the cationic Cetylpyridinium Chloride (CPC) and the non-ionic Octaethylene glycol monodecyl ether (C10E8). Dynamic and Electrophoretic Light Scattering have been used to probe variations in size and surface charge of the vesicles. The surfactants effect on the membrane permeability was investigated by measuring the fluorescence of SUVs secluding the fluorophore calcein. All the surfactants perturb the bilayer inducing graded dye leakage. Irrespective of the chemical nature of the surfactant, the membrane leakage follows the same sigmoidal master curve when it is plotted against the ratio surfactant concentration/cmc. The membrane leakage is negligible below cmc/2 and above such a value increases up to the cmc where all the dye has been fully released. For ionic SDS and CPC the dependence of leakage halftime on such a scaled concentration is the same irrespective of the charge of the surfactant and the vesicles. The nonionic surfactant C10E8 induces the dye release from the SUV two orders-of-magnitude faster than the ionic surfactants. These results show that the rate-determining parameter for the permeabilization of the lipid bilayers is the electrostatic penalty to the flip-flop required to transport the surfactant inside the vesicle.

Mechanism of Efficient Adsorption of Na Atoms on Electron-Deficient Doped MoS2 for Battery Electrodes

Due to the similarities in electrochemical and physicochemical properties of sodium and lithium, sodium-ion batteries are an attractive substitute for lithium-ion batteries. The selection of appropriate electrode materials for $\mathrm{Na}$-ion batteries is an important step to achieve high stability and theoretical capacity. Here, the effects of heteroatom doping and charge variation on the ability of the ${\mathrm{Mo}\mathrm{S}}_{2}$ substrate to capture $\mathrm{Na}$ ions are studied using first-principles calculations. The results show that the interaction between $\mathrm{Na}$ ions and the ${\mathrm{Mo}\mathrm{S}}_{2}$ substrate is enhanced by electron deficiency or substituting a $\mathrm{S}$ atom with a dopant atom (X) with fewer valence electrons (X = $\mathrm{B}$, $\mathrm{Al}$, $\mathrm{Ga}$, $\mathrm{In}$, $\mathrm{C}$, $\mathrm{Si}$, $\mathrm{Ge}$, $\mathrm{Sn}$, $\mathrm{N}$, $\mathrm{P}$, $\mathrm{As}$, $\mathrm{Sb}$). In contrast, adding electrons to the ${\mathrm{Mo}\mathrm{S}}_{2}$ substrate weakens its interaction with $\mathrm{Na}$. We further analyze the diffusion barrier, open-circuit voltage, and theoretical capacity of hypothetical $\mathrm{Na}$-ion batteries using doped $X\text{\ensuremath{-}}{\mathrm{Mo}\mathrm{S}}_{2}$ (X = heteroatom) as electrode materials. We find that $\mathrm{Al}\text{\ensuremath{-}}$ or $\mathrm{Si}$-doped ${\mathrm{Mo}\mathrm{S}}_{2}$ can serve as good electrode materials for $\mathrm{Na}$-ion batteries, with a high theoretical capacity that exceeds 700 mAh/g. This work provides practical guidance for the development of electrode materials of $\mathrm{Na}$-ion batteries using two-dimensional materials.

Investigation on performance degradation due to induced interface trapped charges on HSO based FDSOI NCFET and sustaining it through back-gate bias

In this article, a variant of doped HfO2 based ferroelectric capacitor i.e. silicon doped HfO2 (hafnia-silica/HSO) is investigated for analytical feasibility and viability for negative capacitance FET (NCFET) applications. Investigations are carried out extensively using well calibrated and validated numerical simulations to find out the optimum ferroelectric thickness (tf) of HSO thin-film for the NCFET to operate in hysteresis-free regime. The optimized NCFET is then subjected to the variation of back-gate bias (V ) to exploit threshold-voltage () shift phenomena might further improve NCFET performance. In continuance, the optimized NCFET has been introduced with interface trap (+Nit) charges at the oxide–semiconductor interface to emphasize on the reliability deflation caused at process level design. Hence, this has allowed us to concisely observe and analyse performance degradation aspect of the NCFET with numerical simulations. Also, a feasibility to recuperate the degraded performance caused by +Nit with utilizing −V is carried out. The performance metrics used in the numerical simulation for the evaluation of HSO ferroelectric NCFET are: sub-threshold slope, charge variation with gate-voltage and ferro voltage, surface potential, , drain-current and amplification factor.

Correlation between frictional heat and triboelectric charge: In operando temperature measurement during metal-polymer physical contact

In operando techniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operando temperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operando temperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact.