Search

As investigations in the biomedical applications of plasma advance, a demand for describing safe and efficacious delivery of plasma is emerging. It is quite clear that not all plasmas are "equal" for all applications. This Perspective discusses limitations of the existing parameters used to define plasma in context of the need for the "right plasma" at the "right dose" for each "disease system." The validity of results extrapolated from in vitro studies to preclinical and clinical applications is discussed. We make a case for studying the whole system as a single unit, in situ. Furthermore, we argue that while plasma-generated chemical species are the proposed key effectors in biological systems, the contribution of physical effectors (electric fields, surface charging, dielectric properties of target, changes in gap electric fields, etc.) must not be ignored. [ABSTRACT FROM AUTHOR]

In this paper, we establish nonlinear ellipticity of the equation of contact instantons with Legendrian boundary condition on punctured Riemann surfaces by proving the a priori elliptic coercive estimates for the contact instantons with Legendrian boundary condition, and prove an asymptotic exponential C ∞ -convergence result at a puncture under the uniform C 1 bound. We prove that the asymptotic charge of contact instantons at the punctures under the Legendrian boundary condition vanishes. This eliminates the phenomenon of the appearance of spiraling cusp instanton along a Reeb core, which removes the only remaining obstacle towards the compactification and the Fredholm theory of the moduli space of contact instantons in the open string case, which plagues the closed string case. Leaving the study of C 1 -estimates and details of Gromov-Floer-Hofer style compactification of contact instantons to [27], we also derive an index formula which computes the virtual dimension of the moduli space. These results are the analytic basis for the sequels [27–29] and [36] containing applications to contact topology and contact Hamiltonian dynamics. [ABSTRACT FROM AUTHOR]

Utilization of electro‐responsive biomaterials with antibacterial properties is advantageous for facilitating septic wound healing and tissue regeneration. However, the dose‐response effects of electrical stimuli from these materials against bacteria are not rigorously characterized, and achieving synergy of bactericidal and pro‐regenerative effects of biomaterials remains a major challenge. Here, a graded series of flexible BaTiO3/P(VDF‐TrFE) electroactive nanocomposite membranes (EMs) are developed with varying surface charge intensities, to serve as antibacterial dressing for septic wound healing. EMs display broad‐spectrum antibacterial effects against both Gram‐positive and Gram‐negative bacteria in a dose‐dependent manner, depending on the magnitude of their surface electrical potential. Mechanistically, the surface charge of EMs increase intracellular levels of reactive oxygen species within bacteria cells, which in turn caused oxidative damage to the bacterial membrane, thereby suppressing bacterial activity and biofilm formation. Moreover, in vivo studies demonstrated that EMs effectively inhibited S. aureus infection and accelerated wound healing in a mouse skin defect model, as well as ameliorated P. gingivalis‐mediated periodontal inflammation in a mouse periodontitis model. Hence, this study optimizes the antibacterial properties of electroactive materials and characterizes the dose‐response effects of surface electrical charge against bacteria, thus validating the therapeutic applications of electroactive biomaterials in combating bacterial infection. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of destruction and reassembly of vesicular structure of niosomes as a result of purification by centrifugation. • Significant loss of the encapsulated cargo due to centrifugation. • Mechanism and energy landscape of niosome reassembly. • Elastic niosomes (ethosomes) as a way to decrease a destruction of nanocarriers in the mechanical fields and preserve the content of the water core. This paper presents, for the first time, evidence for vesicle destruction and payload loss at the stage of purification of niosome dispersions by centrifugation, an important operation in the assembly of vesicular materials. The ability of niosomes of different compositions to reassemble, i.e., to restore the vesicular structure after destruction in the field of centrifugal forces, was demonstrated by dynamic light scattering and fluorescence spectroscopy. The kinetics of reassembly of vesicular structures is determined by the strength of the centrifugal field and the composition of niosomes. In contrast to ternary compositions, where particle size and modality are essentially unchanged after redispersion of the precipitate resulting from centrifugation, niosome dispersions containing anionic dicetyl phosphate includes micron-sized particles after redispersion, which vary in size over a wide range throughout the observation period. The reassembly process is complicated by the presence of charge on the surface of the niosomes. Elastic niosomes - ethosomes have been synthesised which, due to the high deformability of the shells, are less susceptible to destruction in the centrifugal field and retain the contents of the aqueous core. Using the "energy landscape" approximation, it is shown that vesicular structures assembled during hydration and reassembled after their centrifugation occupy different positions in the energetic pathway of their preparation. The results obtained should also be taken into account when determining the entrapment efficiency, since this procedure uses centrifugation to separate the load. It is important to note that the physical stability of niosomes, which is usually considered in terms of the functional activity of particles, is manifest and should be considered at the material preparation stage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dual-vacancies modulation strategy was employed to construct MoS 2 -CdS-γ. • Radiation process induced uniform growth of small-sized CdS on MoS 2 substrate. • S vacancies in CdS served as trapping centers for photoexcited electrons. • Integration with 1T/2H phases facilitated fast charge transfer and separation. • Dual defect sites synergized with intimate heterojunction to promote H 2 evolution. Precise defect engineering of photocatalysts is highly demanding but remains a challenge. Here, we developed a facile and controllable γ-ray radiation strategy to assemble dual-vacancies confined MoS 2 -CdS-γ nanocomposite photocatalyst. We showed the solvated electron induced homogeneous growth of defects-rich CdS nanoparticles, while the symbiotic •OH radicals etched flower-like 1T/2H MoS 2 substrate surfaces. The optimal MoS 2 -CdS-γ exhibited a H 2 evolution rate of up to 37.80 mmol/h/g under visible light irradiation, which was 36.7 times higher than that of bare CdS-γ, and far superior to those synthesized by hydrothermal method. The microscopic characterizations and theoretical calculations revealed the formation of such unprecedented dual-sulfur-vacancies ensured the tight interfacial contact for fast charge separation. Besides, the existence of 1T-MoS 2 phase further improved the conductivity and strengthened the adsorption interaction with H+ intermediate. Therefore, the radiolytic radical chemistry offered a facile, ambient and effective synthetic strategy to improve the catalytic performances of photocatalytic materials. [ABSTRACT FROM AUTHOR]

The interactions between molecules and electrode surfaces play a key role in electrochemical processes and are a subject of extensive research, both experimental and theoretical. In this paper, we address the water dissociation reaction on a Pd(111) electrode surface, modeled as a slab embedded in an external electric field. We aim at unraveling the relationship between surface charge and zero-point energy in aiding or hindering this reaction. We calculate the energy barriers with dispersion-corrected density-functional theory and an efficient parallel implementation of the nudged-elastic-band method. We show that the lowest dissociation barrier and consequently the highest reaction rate take place when the field reaches a strength where two different geometries of the water molecule in the reactant state are equally stable. The zero-point energy contributions to this reaction, on the other hand, remain nearly constant across a wide range of electric field strengths, despite significant changes in the reactant state. Interestingly, we show that the application of electric fields that induce a negative charge on the surface can make nuclear tunneling more significant for these reactions. [ABSTRACT FROM AUTHOR]

The influence of the cylindrical exposed electrode diameter on distribution and attenuation of the surface charge in surface dielectric barrier discharges is experimentally investigated using the Pockels effect of the Bi12SiO20 crystal. For the actuator with the smaller exposed electrode diameter, more positive charges accumulate closer to the exposed electrode after positive half periodic discharge, while the quantity of positive charges deposited on the surface in a discharge period at the same distance away from the exposed electrode is smaller. At the same time, the smaller the exposed electrode diameter is, the shorter decay time the positive charge filament needs. Combined with thrust generation of actuators, it can be indicated that a positive residual surface charge closer to the exposed electrode may play a more crucial role in the discharge and consequent thrust than one far away from the exposed electrode does. Also, the effect on the discharge of the positive residual surface charge may be greater than that of the negative residual surface charge. More explorations of the residual surface charge have been done by selectively enhancing the discharge of the actuator with a 10 μm exposed electrode using the pulse-AC dual power supply, drawing the same conclusions. [ABSTRACT FROM AUTHOR]

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation. [ABSTRACT FROM AUTHOR]

The electrostatic potential (EP) generated by the protein α-lactoalbumin in the presence of added salt is computed as a thermal average at a given point in space. With this aim, constant pH Monte Carlo (MC) simulations are performed within the primitive model, namely, the solvent is treated as a continuum dielectric. The study of the thermal and spatial fluctuations of the EP reveals that they are remarkably high inside the protein. The calculations indicate that fluctuations inside the protein are mainly due to the asymmetric distribution of the charge groups, while the charge fluctuations of the titratable groups play a minor role. The computed EP matches very well with the one obtained from the Poisson equation for the average charge density in spherical symmetry. The Tanford–Kirkwood multipole expansion reproduces the simulated angular-averaged potential rather accurately. Surprisingly, two of the simplest mean-field models, the linear Poisson–Boltzmann (PB) equation and Donnan potential, provide good estimations of the average EP in the effective protein surface (surface EP). The linear PB equation predicts a linear relationship between charge and surface EP, which is numerically reproduced only if the small ions within the protein are taken into account. On the other hand, the partition coefficients of the small ions inside and outside the protein predicted by Donnan theory reproduce reasonably well the simulation results. [ABSTRACT FROM AUTHOR]

Surface charges of catalysts have important influences on the thermodynamics and kinetics of electrochemical reactions. Herein, we develop a modified version of the grand-canonical potential kinetics (GCP-K) method based on density functional theory (DFT) calculations to explore the effect of surface charges on reaction thermodynamics and kinetics. Using the hydrogen evolution reaction (HER) on the Pt(111) surface as an example, we show how to track the change of surface charge in a reaction and how to analyze its influence on the kinetics. Grand-canonical calculations demonstrate that the optimum hydrogen adsorption energy on Pt under the standard hydrogen electrode condition (SHE) is around −0.2 eV, rather than 0 eV established under the canonical ensemble, due to the high density of surface negative charges. By separating the surface charges that can freely exchange with the external electron reservoir, we obtain a Tafel barrier that is in good agreement with the experimental result. During the Tafel reaction, the net electron inflow into the catalyst leads to a stabilization of canonical energy and a destabilization of the charge-dependent grand-canonical component. This study provides a practical method for obtaining accurate grand-canonical reaction energetics and analyzing the surface charge induced changes. [ABSTRACT FROM AUTHOR]

In this study, we used 2‐Dimmensionnal Ti3C2 MXene as model materials to understand how the surface groups affect their electrochemical performance. By adjusting the nature of the surface terminations (Cl‐, N/O‐, and O‐) of Ti3C2 MXene through a molten salt approach, we could change the spacing between MXene layers and the level of water confinement, resulting in significant modifications of the electrochemical performance in acidic electrolyte. Using a combination of techniques including in‐operando X‐ray diffraction and electrochemical quartz crystal microbalance (EQCM) techniques, we found that the presence of confined water results in a drastic transition from an almost electrochemically inactive behavior for Cl‐terminated Ti3C2 to an ideally fast pseudocapacitive signature for N,O‐terminated Ti3C2 MXene. This experimental work not only demonstrates the strong connection between surface terminations and confined water but also reveals the importance of confined water on the charge storage mechanism and the reaction kinetics in MXene. [ABSTRACT FROM AUTHOR]

Surface complexation models (SCMs) based on Gouy-Chapman theory are often used to describe adsorption of ions onto mineral surfaces. To compensate for the buildup of charge at a solid surface, the composition of the electric diffuse layer next to the surface must balance the surface charge. To calculate the diffuse layer composition, several nonlinear equations and integrals must be solved, usually with an iterative approach. Before convergence, charge balance is typically not fulfilled. One numerical difficulty is that, because of these charge balance errors, the iterative solver may attempt to take the square root of a negative number. Herein, we show that for electrolytes containing only monovalent or divalent ions (i.e., most electrolytes encountered in practice), we can greatly simplify the integrals and eliminate the appearance of complex-valued integrands; it is even possible to derive explicit analytical formulas. Furthermore, using the new method prevents converging to non-physical roots of the Grahame equation, which links surface potential to surface charge. To the best of our knowledge, the presented formulation has not been implemented in geochemical modelling software before, although similar mathematical expressions have been presented in the literature. In Gouy-Chapman theory, ions can only be distinguished by their charges, but this is not consistent with all experimental findings. We present a model that allows for the preferential accumulation of ions in the diffuse layer. The model, which is implemented mathematically by including ion exchange sites with a variable exchange capacity, is flexible and more numerically tractable than the standard models for the diffuse layer. [ABSTRACT FROM AUTHOR]

An analytical model for calculating the pressure of detonation product on the liner surface was presented. Calculation results show that when the liner structure is the same, increasing the inscribed circle diameter of the charge cross section can reduce the influence of the charge nonaxisymmetry, when it is greater than the critical value, that is, 1.66× liner diameter, the pressure on liner surface is distributed axisymmetrically. Therefore, the jet of the shaped charge with isosceles trapezoidal cross section can be prevented from having an offset velocity by the above-mentioned method. This finding is verified through numerical simulation. [ABSTRACT FROM AUTHOR]

Induction skull melting (ISM) technology could melt metals with avoiding contamination from crucible. A long-standing problem of ISM is that the low charge energy utilization and inhomogeneous fields have obstructed its application in many critical metal materials and manufacturing processes. The present work investigated the problem through the structure optimization strategy and established a numerical electromagnetic-field model to evaluate components' eddy current loss. Based on the model, the effect of crucible and inductor structure on charge energy utilization, etc. was studied. Furtherly, the charge energy utilization was increased from 27.1 to 45.89% by adjusting the system structure. Moreover, structure modifications are proposed for enhancing electromagnetic intensity and uniformity, charge soft contact and uniform heating. The work constructed a basis for framing new solutions to the problem through ISM device structure optimization. [ABSTRACT FROM AUTHOR]

The proliferation of urbanization and the integration of new energy sources have stimulated the development of gas-insulated transmission lines and switchgear (GIL/GIS). In particular, the compact DC GIS in offshore converter platforms will significantly reduce footprints for DC switchyards, exhibit exceptional climatic resistance, and facilitate the cost-effective connection of remote offshore wind farms and submarine links. Nevertheless, insulators used in GIS/GIL always suffer from surface charge accumulation under DC stress, which could distort and enhance the local electric field and thus trigger a flashover at the gas–solid interface if it exceeds certain magnitude levels. This susceptibility becomes a major concern affecting the reliability of DC gas-insulated systems. Beyond these engineering-related challenges lie fundamental physics problems involving mechanisms of charge accumulation and charge-induced flashover which still require exploration. To this end, this paper presents an overview of recent advancements on this topic whilst highlighting relevant issues to be addressed. Specifically, the surface charge accumulation phenomena under DC fields are reviewed, and the charging mechanisms are summarized from macroscopic to microscopic perspectives. Further, the correlation between surface charge and surface flashover is discussed. Moreover, recent developments in tailoring methods for surface charging are also presented. Finally, perspectives are given on current research progress and future needs. [ABSTRACT FROM AUTHOR]

The valence‐band electronic structure is one of the most basic properties of materials and ultraviolet photoelectron spectroscopy (UPS) is the most commonly used technique for its measurement. To obtain credible UPS spectra on insulator surfaces, eliminating the charging effects at the surfaces is essential but is very difficult. Here, a reliable measurement for the valence‐band structure of bulk insulators is shown. It has been observed that, during UPS measurements without any charge compensation, the charging on irradiated insulator surfaces reaches its steady state very quickly and the fluctuation of the charging‐induced surface potential is very small. Therefore, the whole UPS spectrum undergoes just a parallel shift and can be calibrated by comparison with the corresponding X‐ray photoelectron spectroscopy (XPS) spectrum even though XPS often has a poorer resolution than UPS. From the calibrated valence‐band spectra, it is found that noticeable electronic energy levels (i.e., the “surface states”) exist in the bandgap, and based on the density of states (DOS) calculations, the surface states are attributed to the truncation of the bulk periodic structure at the surfaces. This work is anticipated to provide a way to obtain the valence band structure and the surface states of bulk insulators which play crucial roles in many physical processes. [ABSTRACT FROM AUTHOR]

The tribovoltaic effect raises an emerging semiconductor energy technology and silicon‐based tribovoltaic nanogenerator (Si‐TVNG) has aroused great attentions. However, the electrical output of Si‐TVNG is extremely unstable due to its complicated mechanism. Here, a competitive mechanism between the built‐in electric field (BEF) and the interfacial electric field (IEF) is proposed to determine the current direction and magnitude of the Si‐TVNG. The results indicate that the natural oxide layer, load pressure, and resistivity of Si significantly affect the IEF and BEF. The natural oxide layer can store surface charges by contact electrification, resulting in a IEF dominant carriers transport process. Conversely, lower resistivity and higher load pressure can reduce the contact resistance, thereby decreasing the surface charges caused by contact electrification and leading to a BEF dominant carrier transport process. This work contributes to deeper understandings of the tribovoltaic effect and further clarifies the theoretical mechanisms of carrier excitation and directional transport. [ABSTRACT FROM AUTHOR]

Particle size dependent wall-loss rates vary widely between Teflon environmental chambers. For instance, the UCR/CE-CERT dual-90 m3 collapsible Teflon chambers (UCR collapsible chamber) measured particle wall-loss rates are relatively insensitive to particle size, while other chambers (e.g., Caltech, GaTech, UC Davis) exhibit a strong dependence of wall loss rates on particle size. Particle wall loss rates in the larger UCR collapsible chambers exceed those reported for some smaller volume chambers. The size-dependent particle wall-loss patterns in the absence of coagulation within the UCR collapsible chambers were experimentally characterized in this work using a monodisperse particle injection method. Electrostatic charges on chamber surfaces were found to dominate the particle deposition in the UCR collapsible chamber. Charged particles ∼50 nm in diameter decay much faster than charged 200 nm particles, but the overall decay enhancement by electrostatics was determined to be smaller for 50 nm particles due to kinetic charging limitations. Particles in the chamber, regardless of initial charge state, approached a chamber-specific charge steady-state, where the charge steady-state for smaller particles was driven by preferential loss of charged particles while the charge steady-state for larger particles was driven by bidirectional diffusion charging. Coagulation was found to be significant when high particle number loadings are present (e.g., 5 × 104 cm−3). Mitigation strategies are needed for environmental chambers susceptible to surface charging (e.g., UCR collapsible chambers) in order to lower the influence from electrostatics. The shape of the particle wall-loss pattern can be used to identify chambers driven by significant electrostatic particle wall-loss. [ABSTRACT FROM AUTHOR]

Zinc oxide (ZnO) has been widely acknowledged as a highly effective photocatalyst for the degradation of organic pollutants. In this study, we presented silver nanoparticles (AgNPs) embedded ZnO foam photocatalyst (Ag−ZnO) on glass substrates by the chemical bath in‐situ co‐deposition method. Our findings demonstrat that at low Ag‐loading content, metallic Ag0 NPs are embedded within the ZnO foam, while at high Ag‐loading content, they accumulates increasingly from inside to the surface of the foam. With the increase of AgNPs loading from 0.1 mM to 1.5 mM, the absorption of Ag−ZnO foams in the visible light region gradually enhances. The photocatalytic degradation efficiency of rhodamine B (RhB) is the highest in Ag−ZnO foams when the Ag loading concentration reaches 0.8 mM, suggesting an optimal content of Ag for enhanced performance. This trend is attributed to the photo‐induced charge transfer behavior of Ag−ZnO samples. The AgNPs embedded inside the ZnO foam enhance the separation of photo‐induced charges and prevent their recombination. As a result, Ag−ZnO(0.8 mM) foam with more photo‐induced holes participate in the photocatalytic reaction, leading to a remarkably high photocatalytic activity. [ABSTRACT FROM AUTHOR]

A stable suspension of nanoparticles is generally achieved by modifying the surface properties of the nanoparticles using a surfactant. This is to create a surface charge on the nanoparticles which prevents them from forming aggregates. This phenomenon is very sensitive to changes in the local environment. Conventional optical tweezers though capable of trapping sub‐micrometer particles are not known to trap single nanoparticles. However, the stability and dynamics of a suspension of nanoparticles can be probed through the changes in the fluctuations of an optically trapped microsphere that has been added to the suspension. Adding microspheres to the nanoparticle suspension can affect the stability depending on the surface charges the microparticles themselves have. The study reports here on the variation of the dynamics of suspended nanoparticles, which have a positive surface charge, when silica microspheres, which are negatively surface charged, are added to the suspension. With the addition of silica beads, there is agglomeration of the nanoparticles. The dynamics of these agglomerated structures are then probed by measuring the Brownian fluctuations of an optically trapped silica bead. These results are in sharp contrast to those of earlier studies carried out with suspensions of identical nanoparticles but with negative surface charge. [ABSTRACT FROM AUTHOR]

The surface charge distribution in a surface dielectric barrier discharge driven by repetitive pulse bias superimposed on AC voltage is measured using the Pockels effect of an electro-optic crystal. The impact of surface charge on surface-breakdown characteristics is investigated by varying the phase of the pulse superimposition. It is demonstrated that the surface charge accumulation varies at different superimposition phases depending on the potential difference between the two electrodes. The accumulated positive/negative surface charge will facilitate the following surface discharge when the AC voltage polarity changes. In addition, different spatiotemporal characteristics of the surface charge distribution are presented when changing the polarity of superimposed pulses. Positive surface discharges are usually easier to develop than negative surface discharges due to their lower breakdown voltage caused by the accumulation of negative surface charges near the edges of exposed electrodes. The decay of positive surface charge is dominated by neutralization of negative surface charge and negatively charged particles (free electrons and negative ions) from the volume above the dielectric. There are two decay modes of positive surface charge: exponential decay and linear decay. [ABSTRACT FROM AUTHOR]

The hazardous plasma environment surrounding Earth poses risks to satellites due to internal charging and surface charging effects. Accurate predictions of these risks are crucial for minimizing damage and preparing for system failures of satellites. To forecast the plasma environment, it is essential to know the current state of the system, as the accuracy of the forecast depends on the accuracy of the initial condition of the forecast. In this study, we use data assimilation techniques to combine observational data and model predictions, and present the first global validation of a data-assimilative electron ring current nowcast during a geomagnetic storm. By assimilating measurements from one satellite and validating the results against another satellite in a different magnetic local time sector, we assess the global response and effectiveness of the data assimilation technique for space weather applications. Using this method, we found that the simulation accuracy can be drastically improved at times when observations are available while eliminating almost all of the bias previously present in the model. These findings contribute to the construction of improved operational models in estimating surface charging risks and providing realistic 'source' populations for radiation belt simulations. [ABSTRACT FROM AUTHOR]

A simple method to create a BiVO 4 –V 2 O 5 photoanode with excellent interfacial contact and self-doping with V4+ and oxygen vacancies was proposed in this study. Direct generation of BiVO 4 within the film through a solid state reaction between Bi 2 O 3 and V 2 O 5 was achieved, resulting in a highly efficient charge separation and a photocurrent density of 6.6 mA cm−2 at 1.23 V vs. RHE. The bulk charge separation efficiency was 95 %. This study highlights the importance of good interfacial contact for suppressing charge recombination and enabling efficient water oxidation. The developed synthesis method can be a practical approach for fabricating advanced photoelectrodes for sustainable water-splitting technologies, enabling carbon-free fuel production. [Display omitted] • Poor interfacial contact limits charge transfer in heterostructured films. • Solid-state reaction between Bi 2 O 3 and V 2 O 5 yields BiVO 4 /V 2 O 5 films. • In situ generation of BiVO 4 ensures intimate contact during the solid-state reaction. • Films exhibit enhanced bulk charge separation with 95 % separation efficiency. • Synthesis method enables a high water oxidation photocurrent of 6.6 mA cm−2. [ABSTRACT FROM AUTHOR]

Tribocharging or frictional electrification is a physical phenomenon that deals with the exchange and accumulation of electrical charges on the surfaces of bodies that are in contact and then separated. Several situations due to an accumulation of charges on the surfaces of materials in contact can lead to undesirable consequences such as adhesion of particles to the walls, or inception of electrostatic discharges. These situations are common in industry, more particularly in pharmaceutical or food processes. Despite several experimental and theoretical works in this field, the electrostatic charging process is not fully understood, due to the complexity of the many chemical and physical factors that can affect the phenomenon. In recent years, several authors have developed experimental devices and theoretical models to evaluate electrostatic charging during pneumatic transport. In this paper, the objective is to assess three models developed by different researchers to describe the charge generated by particle-wall collisions during the pneumatic transport in dilute phase. The predicted charge was compared with the results of a set of experiments conducted by the authors. This study has shown a good agreement between theoretical models and experimental results. However, a theoretical mathematical relationship between the parameters that are used to adjust the correspondence. [ABSTRACT FROM AUTHOR]

Since the Apollo era, lunar dust has been one of the major problems for lunar surface explorations, since these very abrasive and adhesive grains are harmful for both the instruments and the human beings. Normally, the lunar surface can get charged with an electric field of several V/m, which is not strong enough to launch the dust grains from the surface. However, the electric field may be enhanced when the solar wind and the sunlight are shadowed by an obstacle. Such a shadowing effect can be caused by either a natural topographic feature or a man-made object. Here we study the shadowing effect of a lunar lander with particle-in-cell simulations. It is found that the shadowed region is negatively charged, with a surface potential as low as −30 V and an electric field as large as 20 V/m. A local dust cloud is caused by the electrostatic dust transport around the lander, with a number density of about 104 m−3 at 1 m altitude and up to 105 m−3 near the surface. The surface potential is determined by the temperature of solar wind, but a higher temperature can bring a weaker electric field and a smaller dust cloud, due to the enhanced Debye length. The electrostatic dust transport favors a larger shadowed area, caused by either a larger solar zenith angle or a higher lander height. In addition, the dust transport favors a conductive lander surface, where the maximum dust density can reach 106 m−3. Our results are helpful for the future lunar explorations and have general implications in studying the dust environment of other airless bodies. [ABSTRACT FROM AUTHOR]

X-ray photon correlation spectroscopy (XPCS) holds strong promise for observing atomic-scale dynamics in materials, both at equilibrium and during non-equilibrium transitions. Here an in situ XPCS study of the relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) is reported. A weak applied AC electric field generates strong response in the speckle of the diffuse scattering from the polar nanodomains, which is captured using the two-time correlation function. Correlated motions of the Bragg peak are also observed, which indicate dynamic tilting of the illuminated volume. This tilting quantitatively accounts for the observed two-time speckle correlations. The magnitude of the tilting would not be expected solely from the modest applied field, since PMN is an electrostrictive material with no linear strain response to the field. A model is developed based on non-uniform static charging of the illuminated surface spot by the incident micrometre-scale X-ray beam and the electrostrictive material response to the combination of static and dynamic fields. The model qualitatively explains the direction and magnitude of the observed tilting, and predicts that X-ray-induced piezoresponse could be an important factor in correctly interpreting results from XPCS and nanodiffraction studies of other insulating materials under applied AC field or varying X-ray illumination. [ABSTRACT FROM AUTHOR]

Doping and coating techniques are key methods to address volume expansion and capacity reduction associated with metal oxide-based anodes in lithium-ion batteries. This research focuses on combining graphene with SnO2 and Fe2O3. The composite compounds of rGO-Fe2O3-SnO2 exhibited a spherical and fluffy structure, with granular compounds distributed either on the surface of graphene or between its lamellar layers. 0.4% rGO-Fe2O3-SnO2 demonstrated the most favorable cycling performance and rate capability, with an initial discharge specific capacity of 1439.63 mAh/g and remained relatively stable at approximately 512.28 mAh/g after 1000 cycles. The incorporation of graphene reduced contact resistance and charge transfer resistance, which effectively mitigated the volume expansion phenomenon and enhanced the electrochemical stability. [ABSTRACT FROM AUTHOR]

This study investigates the surface charging and electrophoretic motion of polyethylene glycol-rich (PEG-rich) micro-droplets in dextran-rich solutions or dextran-rich micro-droplets in PEG-rich solutions. The electrophoretic velocities of the droplets were measured in a centimeter-sized chamber under an optical microscope. It was found that the direction of electrophoretic motion of both the PEG-rich droplets and dextran-rich droplets is opposite to the applied electric field, meaning that both the PEG-rich droplets and dextran-rich droplets are negatively charged. The electrophoretic velocity is independent of droplet size but proportional to the electric field strength. Increasing the NaCl concentration reduces the electrophoretic velocity of PEG-rich droplets and increases it for dextran-rich droplets, suggesting different surface charge changes due to ion affinity. The charge densities and velocities are affected by the PEG and dextran mass fractions. Physical models for droplet surface charging under different conditions were proposed to explain the experimental results. [ABSTRACT FROM AUTHOR]

Spacecraft are exposed to harsh radiation environments. These dynamic radiation environments present significant threat to mission performance when charge accumulation and dissipation is not adequately mitigated. EMA3D Charge is a new simulation platform tailored to the study of surface charging, deep dielectric charging, and radiation hardening of spacecraft and their components. Charge implements multiple solvers capable of co-simulating: finite element electromagnetics, boundary element method surface charging, particle transport and particle-in-cell. The multiple solvers facilitate model reuse and enable powerful physical analysis not possible with separate, individual solvers. The solvers include a three-dimensional particle transport tool, a surface charge balance solver, and a finite-element-method electromagnetic solver that supports both quasi-static and full-wave (or fully electrodynamic) solutions. This article summarizes the solvers, example applications, and validation compared to accepted numerical solutions for spacecraft in the space plasma environment. [ABSTRACT FROM AUTHOR]

The influence of a surface electric charge on the character and properties of wave motion along the free surface of a viscous homogeneous fluid is investigated by analytical asymptotic methods. Expressions describing the dispersion relations of the wave-motion components are obtained. The phase and group velocities of the structures forming wave motion are determined. [ABSTRACT FROM AUTHOR]

The slow charge reactions at the semiconductor surface severely encumber the photocatalysis applications, which are elusive and complicated in a serial charge excitation-separation-reaction process. Both experimental and theoretical studies are essential in this area. Here, a classical numerical calculation of the charge reaction microkinetic is developed based on a simple consecutive charge separation and reaction model, a conservation law of photogenerated charges, and differential analysis. Several reaction conditions have been discussed to elucidate how a fast charge separation and reaction rate constant influence the apparent reaction kinetics. It is shown that a slower charge separation rate strongly limits the detection of higher-order reaction rates, and higher-order kinetics can be detected with all other processes faster than the reactions. This numerical calculation projects the possible limitations of kinetics study by transient techniques. [ABSTRACT FROM AUTHOR]

The influence of a surface electric charge on the character and properties of wave motion along the free surface of a viscous homogeneous fluid is investigated by analytical asymptotic methods. Expressions describing the dispersion relations of the wave-motion components are obtained. The phase and group velocities of the structures forming wave motion are determined. [ABSTRACT FROM AUTHOR]

The surface conductivity influences the etched pattern profiles in the plasma process. In the dielectric film etching, it is vital to reduce the charging build-up, which bends the trajectory of incoming ions for highly anisotropic etching. A significant increase in surface electric conductivity of SiO2 films was observed when exposed to down-flow plasmas containing hydrogen fluoride (HF) at cryogenic temperature (−60 °C). This phenomenon can be attributed to two factors: (i) the absorption of HF and/or its compounds and (ii) the presence of H2O, which is likely originating from the etching by-product of SiO2 and/or within the reactor. Comparing the surface electric resistance of the samples treated with HF plasmas to that of CF4/H2 and C4F8/H2 plasmas, we found that HF plasma treatment enables to be approximately three and six orders of magnitude lower. By using in situ x-ray photoemission spectroscopy, it was revealed that the presence of HF and/or its compounds and H2O were absorbed on the sample surface at −60 °C. These results strongly suggest that the cryogenic plasma etching with HF-contained gases can be used to alleviate the charge build-up issues. [ABSTRACT FROM AUTHOR]

Poly(lactic) acid (PLA) is a bio-compatible polymer widely used in additive manufacturing, and in the form of cellular foam it shows excellent mechanical and piezoelectric properties. This type of structure can be easily 3D-printed by Fusion Deposition Modelling (FDM) with commercially available composite filaments. In this work, we present mechanical and electrical investigations on 3D-printed low-cost and eco-friendly foamed PLA. The cellular microstructure and the foaming degree were tuned by varying extrusion temperature and flowrate. The maximum surface potential and charge stability of disk samples were found in correspondence of extrusion temperature between 230 and 240 °C with a flowrate of 53–44% when charging on a heated bed at 85 °C. The cells' morphology and correlated mechanical properties were analyzed and the measured piezoelectric d 33 coefficient was found to be 212 pC/N. These findings show the importance of printing parameters and thermal treatment during the charging process in order to obtain the highest charge storage, stability and material flexibility. These results suggest that 3D-printed cellular PLA is a promising sustainable material for sensing and energy-harvesting applications. [ABSTRACT FROM AUTHOR]

Cancer is a public health problem throughout the world as incidence and mortality rates are increasing year after year. Although conventional therapies such as chemotherapy and radiation show favorable results against this disease, the side effects it causes throughout the body reduce the quality of life of the patient. Therefore, nanomedicine offers us new promising tools to attack cancer through the innovation of nanodrugs, to increase the therapeutic response, reduce dosage, and without generating as many side effects as conventional therapies. For the design of nanodrugs, it is essential to know the biological barriers of the organism and the cancer barriers faced by nanodrugs, such as cell membrane openings, the solubility of the drugs to be transported, and surface electric charge and the protein corona. Due to the aforementioned, the purpose of this review article is to delve into the long journey that nanodrugs undertake from the moment they are administered until they are internalized in tumor cells, taking into account some of the biological and molecular challenges that they defy to reach to its final destination, to observe a desired therapeutic response in the cancer patient. [ABSTRACT FROM AUTHOR]

In the plasma etching technique, acquiring a high-quality transfer from the mask pattern onto the substrate under the suppression of the charging effects is of great significance. Most previous publications only focus on studying the charging phenomena on smooth round mask holes. This work shifted the target to an isolated mask hole with a rough edge using a classical particle simulation program, to examine the effects of edge roughness on surface charging for a mask hole. This study adopted the CF4 plasmas, due to the widely used fluorocarbon plasmas for the contact-holes. Simulated results indicate that the mask holes with various shapes present differences in electric field (E -field) strength distribution, etching rate and profile evolution, relying on some condition parameters (roughness and reflection probability on the mask surface). The larger the dominant wavelength (DW), the more uniform the E -field distribution around the edge of the mask hole will be. The simulation of the profile evolution further confirmed that the deformation is in keeping with the distribution of the E -field. It was further found that the root mean square (RMS) of roughness increases with time in cases of the relatively small values of wavelength (10 and 35 nm) and decreases for other cases. Possible mechanisms behind have been discussed in detail. The findings of this work would shed light on an approach to maintain the pattern integrity. [ABSTRACT FROM AUTHOR]

Electric double layers are ubiquitous in science and engineering and are of current interest, owing to their applications in the stabilization of colloidal suspensions and as supercapacitors. While the structure and properties of electric double layers in electrolyte solutions near a charged surface are well characterized, there are subtleties in calculating thermodynamic properties from the free energy of a system with charged surfaces. These subtleties arise from the difference in the free energy between systems with constant surface charge and constant surface potential. In this work, we present a systematic, pedagogical framework to properly account for the different specifications on charged bodies in electrolyte solutions. Our approach is fully variational—that is, all free energies, boundary conditions, relevant electrostatic equations, and thermodynamic quantities are systematically derived using variational principles of thermodynamics. We illustrate our approach by considering a simple electrolyte solution between two charged surfaces using the Poisson–Boltzmann theory. Our results highlight the importance of using the proper thermodynamic potential and provide a general framework for calculating thermodynamic properties of electrolyte solutions near charged surfaces. Specifically, we present the calculation of the pressure and the surface tension between two charged surfaces for different boundary conditions, including mixed boundary conditions. [ABSTRACT FROM AUTHOR]

In electromagnetism, materials with a polarization density P → or a magnetization density M → are known to exhibit a bound surface charge density σ b = P → · n ̂ or a surface current density κ → b = M → × n ̂ , respectively, where n ̂ is the unit vector perpendicular to the material boundary surface, directed outward. These expressions can be obtained from volume integrations for the electric potential V, or the magnetic vector potential A → , in which the integrals are restricted to the material volumes delimited by their respective boundaries. In that case, applying the divergence theorem leads to surface integrals on material boundaries and to the above-mentioned surface quantities. In this paper, a simple derivation is presented, which shows that both σb and κ → b are included in the expressions for the volume charge or current densities, provided that the divergence and curl operators are evaluated at the boundary so as to account for discontinuities at interfaces. [ABSTRACT FROM AUTHOR]

In this work, a new original justification of an homogenized model for ionic diffusion in porous media is proposed. The approach used enables to specify clearly the domain of validity of this homogenized model, involving a source term characterizing the electrical double layer effect at the macroscale. This homogenized model is obtained from the formal periodic homogenization of a Nernst-Planck-Poisson system at the pore scale accounting for conductivity of the solid phase which is generally neglected. The Poisson equation is defined in both fluid and solid phases and the discontinuity of fluxes at the solid-fluid interface is modeled by a jump of the electrical field, linked to the surface electrical charge of the solid interface. Numerical simulations are carried out at the scale of the unit cell to underscore the influence of the contrast on the electrical permittivity between fluid and solid phases. The comparison of the concentrations and the electrical potential given at the macroscale by the homogenized model and by a direct pore scale model reveals the accuracy of the homogenized model which is very simple to use. [ABSTRACT FROM AUTHOR]

In recent years, the Lunar south pole region (SPR) has become the focus of future explorations due to its special illumination condition and the possible water ice in permanently shadowed craters around it. The Shackleton crater locates almost exactly at the Moon's south pole and has become the hottest destination for several landing missions, including the Chang'E-7 mission. However, people still know little about the electric potential and the dust environment around this crater. In this paper, we develop an analytical model to study the surface potential and the electrostatic dust transport around the crater. It is found that the crater's floor can be negatively charged due to the topographic shielding, and the surface potential is as low as −175 V on the leeward crater wall. Accordingly, a large number of charged dust grains can be emitted from the leeward crater wall, with a maximum height of about 10 km and a horizontal distance of about 40 km, which brings a local dust cloud around the crater. Both the topographic shielding and the local dust cloud are qualitatively verified by a numerical simulation, in which a typical dust density of 104−105 m−3 is found near the crater. Our results are important to the environmental assessment for future explorations near the crater. Furthermore, the results are helpful to understand the surface charging and the electrostatic dust transport on the other airless bodies. [ABSTRACT FROM AUTHOR]

Robust, nanoscale light-emitting devices are attractive for emerging photonic and quantum engineering applications. However, conventional approaches suffer from fabrication challenges or lack the potential to address individual nanostructures, such as quantum dots. In this paper, we present a device that can produce electrically driven light emission from a single quantum dot using a single carbon nanotube as the charge injection contact. The device has a metal-oxide-semiconductor capacitor structure and operates based on an unconventional mechanism of electroluminescence, which relies on the use of bipolar voltage pulses. The proposed device can be fabricated in a simple manner using conventional lithographic processes, offering a scalable approach toward the development of optoelectronic devices at the single dot level. [ABSTRACT FROM AUTHOR]

Surface flashover across an insulator in a vacuum is a destructive plasma discharge which undermines the behaviors of a range of applications in electrical engineering, particle physics and space engineering, etc. This phenomenon is widely modeled by the particle-in-cell (PIC) simulation, here the continuum and kinetic simulation method is first proposed and implemented as an alternative solution for flashover modeling, aiming for the prevention of unfavorable particle noises in PIC models. A one dimension in space, two dimensions in velocity kinetic simulation model is constructed. Modeling setup, physical assumptions, and simulation algorithm are presented in detail, and a comparison with the well-known secondary electron (SE) emission avalanche analytical expression and existing PIC simulation are made. The obtained kinetic simulation results are consistent with the analytical prediction, and feature noise-free data of surface charge density as well as fluxes of primary and SEs. Discrepancies between the two simulation models and analytical predictions are explained. The code is convenient for updating and to include additional physical processes. The possible implementations of outgassing and plasma species for the final breakdown stage are discussed. The proposed continuum and kinetic approach are expected to inspire future modeling studies for the flashover mechanism and mitigation. [ABSTRACT FROM AUTHOR]

Results of studying the process of fine milling of α-Al2O3 in the presence of polyethylene glycol (PEG) and an antistatic composition are presented. It is shown that the main reason for agglomeration of fine particles is the effect of appearance of an electrostatic surface charge. Introduction of PEG prevents appearance of a "pseudo-viscous milling medium", removing the excess electrostatic charge at the surface of newly formed ultrafine particles, and also intensifies the wear process of primary alpha-alumina crystals. The antistatic composition successfully neutralizes a surface electrical charge, but does not exhibit a milling intensifier effect. [ABSTRACT FROM AUTHOR]

A small specific surface area and severe charge carrier recombination greatly limit the photocatalytic efficiency of semiconductors. Herein, we developed a novel wet-chemical intercalation strategy by using the NaBH4 reagent for in situ intercalation-assisted expansion and surface/interface reconstruction of Bi4TaO8Br, which exhibits an enhanced specific surface area and charge carrier separation features. This work highlights intercalation of semiconductors for achieving enhanced photocatalytic performance and provides a new idea to synergistically regulate the morphology and surface/interface composition of semiconductors. [ABSTRACT FROM AUTHOR]

As trapping sites for surface charges, the surface trap is an important factor affecting the insulation performance of the epoxy–SF6 interface, which is closely related to the microstructure and its evolution. However, existing studies often ignore the effect of the degradation of the epoxy surface on the surface traps and charge accumulation during the long-term service of the insulation system. In this study, the surface physicochemical evolution and its influence on surface traps of a typical epoxy–SF6 insulation structure were researched under a DC-temperature gradient condition, and an evolution mechanism of surface traps was proposed. The results show that the free radicals introduced during the material degradation process increase the density and depth of both positive and negative charge traps on the epoxy surface. The effect of free radicals formed by the cleavage of epoxy molecules on the electronic orbital and molecular electrostatic potential of epoxy molecules is the intrinsic reason for the evolution of surface trap evolution. This work may help to understand the long-term evolution mechanisms of the physicochemical characteristics of the epoxy–SF6 interface in DC field and may provide a theoretical basis for the long-term failure mechanism revealing and the insulation performance enhancement. [ABSTRACT FROM AUTHOR]

E-beam voltage contrast inspection is a very common method for in-line detection of many key defect types for rapid yield learning during technology development. Generally, the wafer surface is charged positive, but sometimes charging the wafer surface negative makes more sense. This paper reviews four advantages that negative charging may provide. Switching from positive to negative charging is typically achieved using landing energy and/or extraction voltage. A third control knob is introduced and demonstrated using three common inspection layers, contact chemical mechanical polish (CMP), 3D NAND wordline shorts and 3D NAND wordline opens. [ABSTRACT FROM AUTHOR]

In the case of multipoint initiation of the side surface of a cylindrical charge in a section perpendicular to the axis, a detonation wave with a complex gas-dynamic structure is formed, which has the shape of a polygon with vertices at wave conjugation points. The sides of the polygon are always convex toward the charge axis. It is stated that a smooth cylindrical detonation wave with reverse curvature can be obtained by using special devices at initiation points: lenses made of an inert material. The dynamic characteristics of the material are experimentally determined, and the method for constructing the lens profile is substantiated. The operation of an initiation node and the formation of a cylindrical detonation wave in a charge are mathematically modeled. The specific features of the operation of a single initiating node and a node that is part of the experimental assembly are shown. The dynamics of axisymmetric compression by a converging detonation wave is presented and compared with calculations. [ABSTRACT FROM AUTHOR]

Improving the utilization rate of loaded-drugs is of huge importance for generating chitosan-based (CS) micro-carriers. This study aims to fabricate a novel CS microspheres co-delivered curcumin (Cur) and gallic acid (Ga) to assess drug loading and release kinetics, the blood compatibility and anti-osteosarcoma properties. The present study observes the interaction between CS and Cur/Ga molecules and estimates the change in crystallinity and loading and release rate. In addition, blood compatibility and cytotoxicity of such microspheres are also evaluated. Cur-Ga-CS microspheres present high entrapment rate of (55.84 ± 0.34) % for Ga and (42.68 ± 0.11) % for Cur, possibly attributed to surface positive charge (21.76 ± 2.46) mV. Strikingly, Cur-Ga-CS microspheres exhibit slowly sustainable release for almost 7 days in physiological buffer. Importantly, these microspheres possess negligibly toxic to blood and normal BMSC cells, but strong anti-osteosarcoma effect on U2OS cells. Overall, Cur-Ga-CS microspheres are promising to become a novel anti-osteosarcoma agent or sustainable delivery carrier in biomedical applications. [ABSTRACT FROM AUTHOR]