Charge Pattern Research Articles

Investigation of an electro-osmotic micromixer with heterogeneous zeta-potential distribution at the wall

In this study, the effects of zeta-potential, Debye-Huckel parameter and Reynolds number on electrokinetic mixing through heterogeneous microchannels are investigated. In previous studies, relatively complicated approaches were applied to examine the electrokinetically produced vortices; on the other hand, a relatively simple innovative micromixer consisted of a non-homogeneous rectangular microchannel with the prescribed arrangements of zeta-potential at the walls is considered in this paper. In other words, the mentioned microchannel has heterogeneous zeta-potential distribution at its wall, while other surface properties are assumed to be uniform and homogenous. Moreover, in order to investigate the mixing efficiency of microfluidic devices based on the electroosmotic flow is proposed. Actually, in the electroosmotic phenomenon, the fluid flow is caused by applying a potential across the microchannel. To achieve the electro-osmotic mixing, the Navier-Stokes, Nernst-Planck, Laplace and convection-diffusion equations are solved numerically for the velocity field, ions distribution, electrical potential, and concentration field, sequentially. Having examined the results, one can easily figure out that the performance of electro-osmotic micromixers intensively depends on the wall zeta-potential value and its distribution. Moreover, it can be inferred that the mixing efficiency is really dependent on Debye-Huckel or Reynolds number so that it will increase as soon as theses mentioned parameters decreases. One of the most important achievements of this paper is that a better mixing performance can be attained by the asymmetric charge pattern. In other words, it is really essential to arrange the charge pattern more asymmetric to achieve the highest mixing efficiency.

Numerical study on mixed charging process and gas-solid flow in COREX melter gasifier

We conducted a numerical study of the mixed charging process and gas-solid flow in the COREX melter gasifier by combining discrete element method (DEM) with computational fluid dynamics (CFD). A full-scale COREX melter gasifier model was established to investigate the charging and blasting processes. The model was validated by comparing with the experimental results under similar conditions. The particles above the raceway region descended faster than those near the centre and the wall. With increasing gas velocity, a larger high-velocity airflow region was formed at the tuyere inlet with increased raceway area. In addition, mixed charging pattern had a significant effect on radial ore-to-coal ratio. The ratio was larger in areas where the relative thickness of DRI was significantly larger than that of coal, and was large above the raceway. The upper packed bed structure had a negligible effect on raceway shape and size. Nevertheless, the gas velocity distribution in the packed bed was affected by the burden distribution, which had less fluctuation in the region where the burden was evenly distributed. The findings facilitate a better understanding of burden distribution and gas-solid flow in the COREX melter gasifier.

Postfusion structure of human-infecting Bourbon virus envelope glycoprotein

Thogotoviruses are important zoonotic viruses infecting a variety of domestic animals, as well as humans. Among these viruses, Bourbon virus (BRBV) is one of the several human-infecting members, which emerged in the US in recent years and caused human deaths. Here, we report the crystal structure of the BRBV envelope glycoprotein in the postfusion conformation. The structure adopts the typical fold of a class III viral fusion protein and displays an extensive positively charged electrostatic potential pattern, which resembles the glycoprotein of Dhori virus and is consistent with our previous predictions. In addition, compared to other previously defined class III viral fusion proteins, the structures of all thogotovirus glycoproteins and homologs are more similar to herpes virus glycoprotein Bs than to the rhabdovirus G proteins. Thus, class III viral fusion proteins are quite diverse in structure, and sub-classes may have developed during evolution.

Modulation of Charge Density and Charge Polarity of Nanopore Wall by Salt Gradient and Voltage.

Surface charge plays a very important role in biological processes including ionic and molecular transport across a cell membrane. Placement of charges and charge patterns on walls of polymer and solid-state nanopores allowed preparation of ion-selective systems as well as ionic diodes and transistors to be applied in building biological sensors and ionic circuits. In this article, we show that the surface charge of a 10 nm diameter silicon nitride nanopore placed in contact with a salt gradient is not a constant value, but rather it depends on applied voltage and magnitude of the salt gradient. We found that even when a nanopore was in contact with solutions of pH equivalent to the isoelectric point of the pore surface, the pore walls became charged with voltage-dependent charge density. Implications of the charge gating for detection of proteins passing through a nanopore were considered, as well. Experiments performed with single 30 nm long silicon nitride nanopores were described by continuum modeling, which took into account the surface reactions on the nanopore walls and local modulation of the solution pH in the pore and at the pore entrances. The results revealed that manipulation of surface charge can occur without changing pH of the background electrolyte, which is especially important for applications where maintaining pH at a constant and physiological level is necessary. The system presented also offers a possibility to modulate polarity and magnitude of surface charges in a two-electrode setup, which previously was accomplished in more complex multielectrode systems.

Multi-airport privatization in a Japanese region with trip-chain formation

This study investigates how multi-airport privatization in a tourism region would affect the regional air transport market. An optimization model is developed to formulate the objectives of the three stakeholders, namely airports, airlines, and travelers, to evaluate the market outcomes in different cases. Leisure trip-chain travelers are specifically considered in the presented model, as such a group-level privatization approach has a greater impact on the decisions of trip-chain travelers. As a case study, we select the Hokkaido region in Japan, which is planning to privatize seven airports as a group in 2020, and estimate demand, the profits of airports and airlines, the consumer surplus, and the total surplus in the cases of public operation, airport profit maximization, and single-till and dual-till approaches. The results show that (1) multi-airports privatization enables operator to coordinate airport charges among the group to improve the total surplus. The optimal pattern of airport charges can vary according to the proportion of potential leisure demand. (2) The positive impact of airports’ pricing coordination in a dual-till approach is more limited than that in a single-till approach. (3) Airport charges may not be coordinated in the case of airport profit maximization, even when potential leisure demand is very high; this decreases the consumer surplus and total surplus.

Electrical surface charge patterns induced by droplets sliding over polymer and photoresist surfaces

We have studied the generation of surface charge distributions on polymer surfaces due to the deposition, motion and evaporation of liquid droplets. Using liquids with different static dielectric constants, we found that the magnitude of the surface charge conforms well to the Boltzmann relation for the dissociation probability of ions in solution, indicating that the phenomenon is electrokinetic in nature. The origin of the sensitive dependence of the surface charge on the substrate thickness was identified to be an image charge effect. Experiments on polycarbonate and chemically-amplified photoresist yield surface charges of opposite polarity. By varying the photoresist composition, we identified the leaching of negative quencher ions as the reason for the charge inversion.

Charge Regions Indicated by LMA Lightning Flashes in Hokuriku's Winter Thunderstorms

AbstractThe charge distribution of some cells in three winter thunderstorms in the Hokuriku region of Japan is investigated based on Lightning Mapping Array (LMA) flash data. The vertical arrangements of charge regions involved in lightning discharges suggest diverse charge patterns, including quad‐polar, tripole, positive dipole, inverted dipole, and inverted tripole. The riming electrification between graupel and ice crystals or their aggregations are thought to be responsible for the electrification of most cells. The charging process between snow/aggregates and ice crystals may be responsible for some inverted charge structure that occurred above 0 °C isotherm and accompanied with weak radar echoes. Convection indicated by the vertical development of radar reflectivity appears crucial to shaping the diverse charge distribution patterns by determining which charging mechanisms occur and where; it also influences changes in height or even the disappearance of the charge regions. The charged cores are distributed from 0.7‐ to 5.3‐km heights and 2‐ to –31‐ °C temperatures, while the distances between adjacent charged cores with opposite polarities change between 0.2 and 3.4 km, with a mean of 1.3 km. The mean flash duration and horizontal distance are 425.0 ms and 19.8 km, respectively. The average height, temperature, and power of flash initiations are 2.8 km, −11.9 °C, and 15.6 dBW, respectively.

Effects of Coke Charging Pattern on Burden Distribution and Normal Force Distribution in COREX Melter Gasifier

Based on the principle of discrete element method (DEM), a 2D slot model of COREX Melter Gasifier (MG) being used to study the burden movement under different coke charging patterns has been established. Two kinds of coke charging patterns were introduced to be used to analyze the burden movement in MG. The burden distribution and normal force distribution were analyzed by using the proposed model at a microscopic level. The results show that the burden movement under different coke charging patterns presents different burden movement phenomenon.

Demand side energy management of EV charging stations by approximate dynamic programming

The high operation cost of the EV charging station (EVCS) is a severe challenge for the development of electric vehicles, which lead to the general shortage of the EVCS. In order to reduce the operation costs of the EVCS, an approximate dynamic programming (ADP) based energy management system (EMS) is proposed for the EVCS equipped with multiple types of chargers (EVCS-MTC). A fuzzy logic guiding system has been designed to allocate each vehicle an appropriate charging spot based on its charging urgency. Multiple EVs can acquire the charging service through a common charger in the EVCS-MTC. In the proposed EMS, the approximate dynamic programming (ADP) and the evolution algorithm (EA) are combined to determine the optimal charging start time for each EV. This characteristic provides the charging device with the maximum autonomy to select the preferred flexible charging pattern, which can prolong the battery lifetime and reduce the communication requirements of the control system. With taking the dynamic electricity price and uncertain future charging demand into account, the proposed EMS can achieve a total cost reduction of over 50% compared with the conventional charging scheme in the numerical studies.

Grid Loading Due to EV Charging Profiles Based on Pseudo-Real Driving Pattern and User Behavior

This paper defines a method for generating individual electric vehicle (EV) charging patterns, and it intends to quantify the realistic loading impact on distribution grid feeders. The inputs are based on the historical driving characteristics of private conventional vehicles from Denmark and home plug-in behavior of EVs from Japan. The first input is used to define properties, such as the daily driven distance and the expected departure and arrival time, which determines the possible home charging window. The second input is used to quantify the probability of performing a domestic charge every day. Because most of the EVs do not need to charge every day, even when considering a 100% EV penetration scenario, the amount of simultaneous charging with domestic single-phase charging power (3.7 kW) determines a coincidence factor lower than 45%. When considering three-phase charging (11 kW), the combined power of the EV population increases only to 50% because of shorter charging sessions. Although the power increase, due to 11-kW charging, is likely to trigger grid components overloading, it is highlighted how uncontrolled distribution of single-phase charging could be responsible for local voltage unbalances.

Quantifying flexibility of residential electric vehicle charging loads using non-intrusive load extracting algorithm in demand response

The increasing penetration of electric vehicles (EVs) has increased the operational burden on power grids during peak load periods. Identifying the charging patterns of residential EV clusters and quantifying their flexibility in demand response (DR) can help grid operators make effective regulatory decisions for balancing grid supply and load. In this study, statistical models are established for the charging patterns (charging start time, charging end time, and charge duration) of residential EVs. A training-free non-intrusive load extracting (NILE) algorithm is proposed. The algorithm is based on different load signatures and power block extremums, and can extract the EV load charged by different charging power. A price-based DR model is established to optimise the charging strategy of EVs, and the flexibility of EVs in DR is quantified according to the change of charging behaviour before and after optimisation. In addition, the validity of the NILE algorithm is verified with a real data set, and the flexibility of the EV cluster in different situations (seasons, weekdays, and weekends) is quantified based on the separated charging data.

Interfacial Junctions Control Electrolyte Transport through Charge-Patterned Membranes.

Distinct transport mechanisms emerge when nanostructured substrates are patterned with multiple chemistries. For example, charge-patterned mosaic membranes possess surfaces functionalized with discrete domains of both positive and negative charge. These oppositely charged domains provide pathways for both the cation and anion from a dissolved salt to permeate through the membrane without violating the macroscopic constraint of electroneutrality. Here, by systematically varying the geometry and size of the charge pattern, we elucidate the molecular interactions that promote the transport of salts under the action of pressure-driven flow. For patterns that consist of equivalent areal coverages of positively charged and negatively charged domains, the effects of the geometric parameters were encapsulated in a single variable, the interfacial packing density, that quantified the fraction of the membrane surface covered by junctions between oppositely charged domains. Experimentally, the transport of symmetric electrolytes (i.e., KCl and MgSO4) increased with the value of the interfacial packing density, while the interfacial packing density did not significantly affect the transport of asymmetric electrolytes (i.e., K2SO4 and MgCl2). Simulations of the electrical potential near the membrane surface demonstrate that for symmetric electrolytes the structural charge heterogeneity reduces the barrier to ion partitioning, thereby promoting salt transport through the membranes. For asymmetric electrolytes, the charge heterogeneity skews the local availability of ions from the stoichiometric ratio of the salt, thus hindering salt transport. These findings demonstrate the promise of accessing transport mechanisms, which could find utility in a diverse range of chemical separations and sensing applications, through chemical patterning of membranes.

Temporal Analysis of Conformers in the Course of pH Scan Directed by Urea-Urease Reaction-A "Protein Clock".

We demonstrate an analytical approach to monitor the effect of pH on protein tertiary structure. An autocatalytic enzyme reaction is used to stimulate refolding of proteins during real-time analysis. The method takes advantage of a nonlinear pH ramp generated by the urea-urease clock reaction. In this study, alterations to the structures of model proteins were monitored by mass spectrometry (charge pattern shift) and fluorometry (tryptophan fluorescence quenching). The pH measurements were conducted at different points of the sample flow line by different methods to minimize artifacts. Interestingly, different protein ions (corresponding to native and unfolded proteins) show distinct temporal mass spectral profiles, which reveal gradual refolding and concomitant deprotonation of higher charge state ions in the course of the clock reaction. Every multiply charged ion of a protein is characterized with its own "clock time". This approach does not require major modification of standard instrumentation. It enables determination of "high sensitivity" pH intervals for small and large molecules within a single experiment. Thus, it can be useful for characterizing the protein folding in response to pH change.

Positive Charge Patterning and Hydrophobicity of Membrane-Active Antimicrobial Peptides as Determinants of Activity, Toxicity, and Pharmacokinetic Stability.

Natural α-helical cationic antimicrobial peptide (CAP) sequences are predominantly amphipathic, with only ca. 2% containing four or more consecutive positively charged amino acids (Lys/Arg). We have designed synthetic CAPs that deviate from these natural sequences, as typified by the charge-clustered peptide KKKKKKAAFAAWAAFAA-NH2, (termed 6K-F17), which displays high antimicrobial activity with no toxicity to mammalian cells. We created a series of peptides varying in charge patterning, increasing the amphipathic character of 6K-F17 to mimic the design of natural CAPs (e.g., KAAKKFAKAWAKAFAA-NH2). Amphipathic sequences displayed increased antimicrobial activity against bacteria but were significantly more toxic to mammalian cells and more susceptible to protease degradation than their corresponding charge-clustered variants, suggesting that amphipathic sequences may be desirable in nature to allow for more versatile functions (i.e., antibacterial, antifungal, antipredator) and rapid clearance from vulnerable host cells. Our approach to clustering of charges may therefore allow for specialization against bacteria, in concert with prolonged peptide half-life.

Marginal Greenhouse Gas Emissions of Ontario's Electricity System and the Implications of Electric Vehicle Charging.

To estimate greenhouse gas (GHG) emission reductions of electric vehicles (EVs) deployment, it is important to account for emissions from electricity generation. Since such emissions change according to temporal patterns of electricity generation and EV charging, this study operationalizes the concept of marginal emission factors (MEFs) and uses person-level travel activity data to simulate charging scenarios. Our study is set in the Greater Toronto and Hamilton Area in Ontario, Canada. After generating hourly MEFs using a multiple linear regression model, we estimated GHG emissions for EV charging at two EV penetration rates, 5% and 30%, and five charging scenarios: home, work and shopping, night, downtown vs suburb, and an optimal low emission charging scenario, matching charging time with the lowest available MEF. We observed that vehicle electrification substantially reduces GHG emissions, even when using MEFs that are up to seven times higher than average electricity emission factors. With Ontario's 2017 electricity generation mix, EVs achieve over 80% lower fuel cycle emissions compared with equivalent sets of gasoline vehicles. At 5% penetration, night charging nearly matches low emission charging, but night charging emissions increase with 30% EV penetration, suggesting a need for policy that can smooth out charging demand after midnight.

Capillary imbibition in pattern charged nanotubes

Capillary imbibition of water plays a significant role in various applications at both macroscopic and microscopic scales. However, it is still unclear how the capillary imbibition would be effected by the surface conditions, in particular, the charge patterns in the nanotubes. In this paper, we discuss the capillary imbibition dynamics in pattern charged nanotubes by molecular dynamics simulations. Two common charge patterns are considered, i.e. the adjacent charge pattern and barred charge pattern. It is found that velocity of the water imbibition in the barred pattern charged nanotube exhibits a strong impediment effect while the adjacent pattern charged nanotube shows no effect. By analyzing the microscopic distribution of the water molecules, it is found that the impediment effect originates from the decreased number of hydrogen bonds between the first monolayer water and the inner water shells, where a hexagonal ice-like hydrogen bond network of the water molecules would be induced in the first monolayer water by the barred charge pattern. The time variations of the filling length of the two charge patterns are also compared with the theoretical predictions in the continuous limit at the inertial and viscous regime respectively. Furthermore, it is also found that the impediment effect could be manipulated by varying the charge value and nanotube radius. Our results suggest a possible way to control the capillary imbibition behavior and it may have significant implications for water treatment, nanoswitches, catalysis engines and biological sensors.

PSO-based optimization for constant-current charging pattern for li-ion battery

A particle swarm optimization algorithm to search for an optimal five-stage constant-current charge pattern is proposed. The goal is to maximize the objective function for the proposed charge pattern based on the charging capacity, time, and energy efficiency, which all share the same weight. Firstly, an equivalent circuit model is built and battery parameters are identified. Then the optimal five-stage constant-current charge pattern is searched using a particle swarm optimization algorithm. At last, comparative experiments using the constant current-constant voltage (CC-CV) method are performed. Although the charging SOC of the proposed charging pattern was 2.5% lower than that of the CC-CV strategy, the charging time and charging energy efficiency are improved by 15.6% and 0.47% respectively. In particular, the maximum temperature increase of the battery is approximately 0.8 °C lower than that of the CC-CV method, which indicates that the proposed charging pattern is more secure.

High-Power Plasma Flows Generated by Nanosecond Vacuum Surface Flashover of Polymeric Materials at 80 kV

In this paper, we studied the process of vacuum surface flashover of several polymeric materials initiated by 80-kV, 15-ns pulses with peak discharge current 3 kA. We measured breakdown propagation speed, energy input to the discharge, full ion charge and directional pattern of the plasma flow, the full energy of the particle flow, propellant mass loss, and thrust for polytetrafluorethylene (PTFE), polyethylene (PE), and polymethyl metacrylate (PMMA). In the case of PTFE, we obtained the maximum absolute values of thrust ( $4.7~\mu \text{N}\cdot \text{s}$ ) and the full energy (66 mJ). The values of average mass velocity for all materials lie in the range of 3–7 km/s; values of the average velocity of ions lie in the range of 60–85 km/s. Directional patterns of charge and mass are similar and have distinct symmetry in equatorial and meridional planes. We estimated the temperature of the dielectric surface within a model of energy transfer from the discharge channel to the surface due to thermal conductivity. We showed that at this power level ( $\sim 10^{7}$ W) and short duration of high-current stage of the discharge ( $\sim 10^{-8}$ s), the propellant is consumed mainly during the stage of plasma channel formation.

Field-dependent charging phenomenon of HVDC spacers based on dominant charge behaviors

Spacers are key components that are used to support high voltage conductors in gas-insulated substations or gas-insulated lines. The analysis of the surface charge patterns on spacers remains a difficult task, which requires a comprehensive understanding of the physical mechanism of the gas-solid interface charging phenomenon. In this letter, we reported a field dependent property of surface charge accumulation patterns on spacers under DC stress. We verified this finding through experiment, and further, we put forward a field-dependent charging model based on dominant charge transport behavior under different electric fields. It was found that the charging characteristics of the spacer are dominated by the Ohmic conduction from the volume below an electric field of 2.5 kV/mm. When the electric field stress is higher than 2.5 kV/mm, the charging property of spacers is dominated by the enhanced gas ionization according to Townsend's law. The correctness of this model was verified by surface charge measurement results in literature studies, and a method for determining the dominant mechanism of charge accumulation under different electric fields was proposed.

Direct growth of graphene-like film microstructure on charge pre-patterned SiO2/Si substrate

For a wide range of practical applications of graphene-like films (GLFs), it is highly desirable to have a material with high uniformity and good electric characteristics. GLFs in this work are defined as graphene films with the crystallite size of several tens of nm. The structure of a CVD-grown GLF is typically disturbed by post-deposition procedures, including transfer and lithography. In this work we aim at the catalyst-free and lithography-free selective deposition procedure, which directly yields the desired GLF pattern on a dielectric substrate, by-passing transfer and lithography, the destructive steps of the manufacturing process. The catalyst-free deposition of graphene-like films can be strongly enhanced by the near-surface electric charge, and in this work we use this effect for selective growth of GLF microstructures. The charge pattern is created by irradiation of the substrate with an e-beam. We study experimental conditions for the selective deposition of GLF from ethanol vapor on SiO2/Si substrate. The e-beam exposure parameters are optimized based on Monte-Carlo simulations and the experimental study of the deposited films Raman spectroscopy and AFM. The electrical properties are studied by the selectively-grown Hall microstructure; it is shown that the film has highly promising characteristics for practical applications.