Initial Charge Density Research Articles

Machine learning assisted mechanism modeling for gas phase electrohydrodynamic system

In this paper, a hybrid physics-data driven model for electrohydrodynamic gas system (EHDGS) was developed by combining artificial neural network (ANN) with mechanism modeling method. ANN was used to correlate the relationship between the variables (electrode distance, diameter of grounding cylinder, applied voltage, electric field gradient, etc.) in a needle-cylinder EHDGS and the initial space charge density. The results showed that the ANN model of nine neurons can well predict the initial space charge density. The coefficient of determination (R2) reaches 0.9874, and the mean absolute error is as low as 0.0067. Subsequently, a hybrid mechanism model where the initial space charge density was predicted from the ANN model was constructed to simulate the needle-cylinder EHDGS. The experiment with the needle-cylinder EHDGS was carried out. The simulation results were in good agreement with the experimental data, demonstrating the reliability of the proposed hybrid model. The electric field distribution, space charge distribution, and flow field distribution behavior of the EHDGS were then analyzed in detail. The effects of key parameters on the flow characteristics of EHDGS were systematically studied, showing that higher voltage and shorter distance give higher flow rate up to 2.5 m/s. The diameter of the cylinder also significantly influences the breakdown voltage. Three dimensionless groups were defined and their effects on spatial charge density distribution were investigated. This study provides both insights and an efficient tool for the design and optimization of EHDGS.

Free iron oxides modulate the surface properties of Benggang soil on Southern China: insights into erosive mechanisms

Benggang, an erosional phenomenon located in southern China, exhibits distinctive characteristics that can have profound ecological and agricultural consequences as well as pose risks to human life. Previous investigations have primarily focused on elucidating the relationships between the physical and chemical attributes of soils collected from Benggang. However, the precise role of free iron oxides in the surface properties of Benggang soil and its contribution to the formation of Benggang remains largely unexplored. In this study, we aim to investigate the role of free iron oxides in Benggang soil by removing them and subsequently introducing goethite to evaluate their impact on the soil’s surface properties. Our results reveal a decrease in the surface charge density of soil colloidal particles with increasing soil depth. Specifically, the uppermost red soil layer exhibits the highest value, followed by the sandy soil and the lowermost clastic layer. Upon removing free iron oxide, we documented reductions of 44.28% (red soil), 20.62% (sandy soil), and 8.70% (clastic layer) in the surface charge density of colloidal particles. The red soil layer presented an over 18-fold increase compared to the initial linear shrinkage, followed by the sandy soil and clastic layer. Notably, the addition of goethite to the iron oxide-free soil layers resulted in the recovery of approximately 81.93%, 121.13%, and 104.35% of the initial surface charge density, respectively. Moreover, significant changes in volume shrinkage were observed, with approximately 97.54% (red soil), 94.75% (sandy soil), and 89.72% (clastic layer) of the initial values being influenced. These findings underscore the substantial influence of free iron oxide on the physicochemical properties of Benggang soil and contribute to a comprehensive understanding of the erosive mechanisms underlying Benggang formation.

Anderson and many-body localization in the presence of spatially correlated classical noise

We study the effect of spatially correlated classical noise on both Anderson and many-body localization of a disordered fermionic chain. By analyzing the evolution of the particle density imbalance following a quench from an initial charge density wave state, we find prominent signatures of localization also in the presence of the time-dependent noise, even though the system eventually relaxes to the infinite temperature state. In particular, for sufficiently strong static disorder we observe the onset of metastability, which becomes more prominent the stronger the spatial correlations of the noise. In this regime we find that the imbalance decays as a stretched-exponential - a behavior characteristic of glassy systems. We identify a simple scaling behavior of the relevant relaxation times in terms of the static disorder and of the noise correlation length. We discuss how our results could be exploited to extract information about the localization length in experimental setups.

Triple high energy nuclear and hadron collisions - a new method to study QCD phase diagram at high baryonic densities

We propose an entirely new method to study the phase diagram of strongly interacting matter by means of scattering the two colliding beams at the fixed target. Here we present the results of simulations of the most central triple nuclear collisions with the UrQMD 3.4 model for the beam center-of-mass collision energies sqrt{s_{NN}} = 2.76 hbox {TeV} and sqrt{s_{NN}} = 200 hbox {GeV}. The main outcome of our modeling is that even at these very high collision energies the initial baryonic charge densities are about 3 times higher than the ones achieved in the ordinary binary nuclear collisions. As a result, for instance, the yields of protons and varLambda -hyperons are strongly enhanced in the triple nuclear collisions. The other prospective applications of this method are briefly discussed. Among them we consider the low energy collisions of three nuclei of lead, passing through an intermediate system with an electric charge of 246 units which exceeds essentially the critical value of 173 and, hence, this may be of crucial importance to study the spontaneous emission of positron-electron pairs from the vacuum. We present the convincing arguments that the triple nuclear collisions method will allow the high energy nuclear physics community to create a new frontier in the studies of the QCD phase diagram and to lift up these studies to an entirely new level.

Computation of Total Electric Field Considering Natural Wind Under High-Altitude UHVDC Transmission Lines

With the rapid development of ultra high-voltage DC (UHVDC) transmission technology, the total electric field problem in high-altitude dc transmission lines is more important. Therefore, this article proposes a calculation model of the ion flow field at high altitude based on the natural wind model and the gas motion theory. First, the initial charge density is assumed, and then, Poisson’s equation is solved by the finite-element method (FEM). The measured wind speed and altitude are introduced into the natural wind model and the ion mobility model, and the natural wind speed and the ion mobility of each node are obtained. Subsequently, the current continuity equation is calculated by this information and the upstream FEM. When the calculation results do not meet the steady-state convergence conditions, the charge density on the conductor surface is iteratively corrected. The calculation model is verified by the measurement results of the ±800-kV UHVDC transmission line at the National Engineering Laboratory for Ultrahigh Voltage Technology (Kunming) of the China Southern Power Grid. The research shows that with the increase of altitude, the ion mobility gradually becomes larger, and the total electric field at ground level also increases. Due to the influence of wind, the peak value of the total electric field at ground level is obviously shifted, and the maximum peak values are on the downwind side. This model in this article can accurately calculate the total electric field of UHVDC transmission lines at high altitude considering the natural wind and provide a reference for the design of transmission lines.

Electrostatic elimination of charged particles by DC-type bipolar electrostatic eliminator

The electrostatic eliminator is widely used to prevent silos from explosions caused by the electrostatic discharge of charged particles. However, electrostatic accidents still happen occasionally. This study investigated charge elimination characteristics of the DC-type bipolar electrostatic eliminator under different configurations of the applied voltages, air velocities, and initial charge densities of particles for helping improve the charge elimination efficiency. The results show that the unipolar corona discharge will lead to reverse charging of particles, while the bipolar corona discharge at a suitable configuration can neutralize the charged particles completely. The upper and lower ionizers in the bipolar electrostatic eliminator should be applied with positive and negative voltages, respectively, and the positive voltage should be greater than the negative one. The suitable configuration of the electrostatic eliminator is insensitive to air velocity due to the simultaneous increase of the charging capability of positive and negative corona discharges with increasing the air velocity. This electrostatic eliminator can neutralize the charged particles with a net negative charge even in the presence of positively charged particles in the mixture. Furthermore, the performance of this electrostatic eliminator on a full-scale silo was examined using a light intensifier to observe the electrostatic discharge inside the silo. The proposed electrostatic eliminator was found to be effective in eliminating the electrostatic discharge in the silo.

Colliding and Fixed Target Mode in a Single Experiment—A Novel Approach to Study the Matter under New Extreme Conditions

Here, we propose a novel approach to experimentally and theoretically study the properties of QCD matter under new extreme conditions, namely having an initial temperature over 300 MeV and baryonic charge density over three times the values of the normal nuclear density. According to contemporary theoretical knowledge, such conditions were not accessible during the early Universe evolution and are not accessible now in the known astrophysical phenomena. To achieve these new extreme conditions, we proposed performing high-luminosity experiments at LHC or other colliders by means of scattering the two colliding beams at the nuclei of a solid target that is fixed at their interaction region. Under plausible assumptions, we estimate the reaction rate for the p+C+p and Pb+Pb+Pb reactions and discuss the energy deposition into the target and possible types of fixed targets for such reactions. To simulate the triple nuclear collisions, we employed the well-known UrQMD 3.4 model for the beam center-of-mass collision energies sNN = 2.76 TeV. As a result of our modeling, we found that, in the most central and simultaneous triple nuclear collisions, the initial baryonic charge density is approximately three times higher than the one achieved in the ordinary binary nuclear collisions at this energy.

Dynamical quantum phase transitions in the one-dimensional extended Fermi–Hubbard model

We study the emergence of dynamical quantum phase transitions (DQPTs) in a half-filled one-dimensional lattice described by the extended Fermi–Hubbard model, based on tensor network simulations. Considering different initial states, namely noninteracting, metallic, insulating spin and charge density waves, we identify several types of sudden interaction quenches which lead to DQPTs. Furthermore, clear connections to particular properties of observables, specifically the mean double occupation or charge imbalance, are established in two main regimes, and scenarios in which such correspondence is degraded and lost are discussed. Dynamical transitions resulting solely from high-frequency time-periodic modulation are also found, which are well described by a Floquet effective Hamiltonian. State-of-the-art cold-atom quantum simulators constitute ideal platforms to implement several reported DQPTs experimentally.

Triple nuclear collisions – a new method to explore the matter properties under new extreme conditions

We suggest to explore an entirely new method to experimentally and theoretically study the phase diagram of strongly interacting matter based on the triple nuclear collisions (TNC).We simulated the TNC using the UrQMD 3.4 model at the beam center of- mass collision energies √SNN = 200 GeV and √SNN = 2.76 TeV. It is found that in the most central and simultaneous TNC the initial baryonic charge density is about 3 times higher than the one achieved in the usual binary nuclear collisions at the same energies. As a consequence, the production of protons and Λ-hyperons is increased by a factor of 2 and 1.5, respectively. Using the MIT Bag model equation we study the evolution of the central cell in TNC and demonstrate that for the top RHIC energy of collision the baryonic chemical potential is 2-2.5 times larger than the one achieved in the binary nuclear collision at the same time of reaction. Based on these estimates, we show that TNC offers an entirely new possibility to study the QCD phase diagram at very high baryonic charge densities.

Transient physical modeling and comprehensive optimal design of air-breakdown direct-current triboelectric nanogenerators

Direct-Current Triboelectric Nanogenerators (DC-TENGs) achieves an direct-current (DC) output instead of traditional alternating-current (AC) output of TENG. Among the various structure designs of DC-TENGs, the air-breakdown DC-TENG has created a record of energy density and an almost constant-current output, which has great potential in practical applications. This paper proposes a transient physical-field model and carries out comprehensive optimal design for air-breakdown DC-TENG. The beneficial breakdown domain (BBD) and harmful breakdown domain (HBD) are introduced to reveal the dynamic mechanism that distinguishes the DC-TENGs from AC-TENGs. Indexes of the breakdown charge ratio (BCR) and leading charge density (LCD) are defined to evaluate the extent to which the high-density surface charge is effectively exploited in electricity generation based on the beneficial breakdown effect. The output characteristics of air-breakdown DC-TENGs are theoretically analyzed, revealing the influence of the load resistance, device structure parameters, and initial charge density. Therefore, the optimal design of air-breakdown DC-TENGs is carried out with a high output power and low matching resistance. Finally, these superior performances are verified by experiments, so that the proposed transient physical model and comprehensive optimization method can be reliably extended to the design of all types of air-breakdown DC-TENG, and promote its application in a wide range of fields.

Low-Cost, Environmentally Friendly, and High-Performance Triboelectric Nanogenerator Based on a Common Waste Material.

With the great progress in human activities and production technologies, the waste inevitably produced causes not only environmental pollution but also resource waste; meanwhile, the mobile and portable electronic devices urgently need a distributed and sustainable energy source to ensure their stable operation. Here, the waste pollutants (milk cartons) generated from daily life, commonly associated with environmental concerns, are instead identified as an available resource for preparing an emerging energy harvester (triboelectric nanogenerator, TENG), which can convert ubiquitous mechanical energy into electric power. Consequently, based on the waste material, the initial charge density of the TENG is as low as 0.035 mC m-2, which can be tremendously improved to 1.00 mC m-2 through combining a charge excitation circuit, achieving efficient energy harvesting. In addition, compared to the common dielectric film, the waste material can reduce the cost and simplify the process of the preparation of TENG. This work provides not only an innovative approach to simultaneously realize environmental protection and energy harvesting but also more material choice for the preparation of a low-cost and high-performance TENG.

1-D fractal model for bentonite colloid diffusion without seepage

This paper investigates the 1-D diffusion process of bentonite particle, which is affected by the friction related to the fractal structure of colloid pore. The expression of the pore tortuosity containing pore fractal dimension is deduced to determine the friction, and the evolution rule of pore fractal dimension during diffusion with bentonite volume fraction is reached. The rationality of the modified fractal model is validated via 1-D diffusion test and nuclear magnetic resonance (NMR). Then the influences of electrolyte concentration, initial volume fraction of bentonite, and surface charge density on the colloid diffusion process are analyzed. The results show that the diffusion of bentonite decreases with the increase of electrolyte concentration, and increases with the increase of initial volume fraction and surface charge density. The interfacial volume fraction is correlated with the concentration of electrolyte solution, but not with the initial volume fraction and surface charge density.

Enhanced thermal and dielectric performance of epoxy resin/aluminum nitride nanocomposites at high temperatures

AbstractThe effects of nano‐aluminum nitride (nano‐AlN) on the thermal conductivity and dielectric performances of epoxy resin (EP) are investigated. The addition of nanoparticles in the materials is characterized. The trap characteristics of the samples are estimated using the surface potential decay (SPD) measurements at high temperatures. The results show that the nano‐AlN fillers are well dispersed in the nano‐AlN composites. The thermal conductivity consistently increases with an increase of the nano‐AlN content. The DC breakdown strength of the EP is enhanced with the addition of the nanoparticles as well, especially for the 0.5 and 1 wt% EP/AlN composites. The DC conductivity of the EP/AlN composites increases more obviously at the high temperature. The initial surface charge density of the samples with the same content of nano‐filler decreases with the increase of the temperature. Both the addition of nanoparticles and high temperature can improve the apparent carrier mobility of the EP sample. The trap density and trap level of the deep traps decreases with the increase of the temperature. It is postulated that shallow traps influence the voltage decay in the EP samples and increase the activation energy and the apparent carrier mobility of the specimens at the high temperature.

Ultrasound-induced generation of multielectron bubbles in liquid helium

Multielectron bubbles provide a unique platform to study electrons in two dimensions and on curved surfaces, at densities which cannot be accessed using electrons on bulk helium or in semiconductor interfaces. Usually, MEBs are created by applying a large electric field and thereby inducing electrohydrodynamical instability on a charged surface of liquid helium. In the present study, we describe a method to create instability of the charged surface using ultrasound, in the presence of small electric fields. The ultrasound was applied close to the charged liquid-vapor interface, resulting in the formation of a liquid column, which breaks into liquid droplets. The mechanical impact of the droplets falling back into the bulk liquid resulted in the formation of highly charged multielectron bubbles. We estimated the initial charge density of the bubbles above the lambda point to be close to ${10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{electrons}/{\mathrm{m}}^{2}$.

Dielectrophoretic Crossover Frequency of Single Particles: Quantifying the Effect of Surface Functional Groups and Electrohydrodynamic Flow Drag Force.

We present a comprehensive comparison of dielectrophoretic (DEP) crossover frequency of single particles determined by various experimental methods and theoretical models under the same conditions, and ensure that discrepancy due to uncertain or inconsistent material properties and electrode design can be minimized. Our experiment shows that sulfate- and carboxyl-functionalized particles have higher crossover frequencies than non-functionalized ones, which is attributed to the electric double layer (EDL). To better understand the formation of the EDL, we performed simulations to study the relationship between initial surface charge density, surface ion adsorption, effective surface conductance, and functional groups of both functionalized and nonfunctionalized particles in media with various conductivities. We also conducted detailed simulations to quantify how much error may be introduced if concurrent electrohydrodynamic forces, such as electrothermal and electro-osmotic forces, are not properly avoided during the crossover frequency measurement.

Features of the Charge State of UHMWPE + α-SiO2 Nanocomposites

This paper presents the results into the study of electret properties of composite materials based on ultrahigh molecular weight polyethylene (UHMWPE) and nano-dispersed amorphous silica filler α-SiO2 (aerosil) depending on the volume content of silicon dioxide and the absorbed dose D γ-irradiation at room temperature using the method of thermally stimulated depolarization (TSD). It was found that introducing up to 5% of spherical nanoparticles of amorphous α-SiO2 silicon dioxide with a diameter of 20 nm in UHMWPE first increases and then reduces the electret characteristics of the composites. UHMWPE + 1% α-SiO2 has the maximum value of the electret potential difference and the stability of the electret state. It was shown that preliminary γ-irradiation affects the electret properties of the studied composite material, which is associated with its increased electrical conductivity and a high charge relaxation rate. The observed increase in the initial surface charge density σel of UHMWPE compositions is associated with the presence of energy traps of injected charge carriers. Based on the analyzing the spectra of TSD, it was shown that the thermal stability of electrets from the UHMWPE composite + 1% α-SiO2 is improved. The nature of the TSD current of pre-γ-irradiated films once again proves that, after γ-irradiation, the injected charges from the corona zone mainly accumulate in the near-surface layers of the irradiated samples. The results of TSD suggest that the relaxation of the electret state in the materials under study occurs due to the bulk conductivity.

Hereditary Effect of the Structure of the Charge on Density, Gas Content, and Processes of Solidification of an Al–Si–Cu Alloy System

The effect of the structure of the initial charge density in liquid and solid states, as well as on the temperature–time parameters of the process of solidification of the AK6M2 alloy (Al–6% Si–2% Cu), is shown. To obtain a coarse-crystal charge (C charge), part of the melt is crystallized in ceramic forms in a sand backfill with a cooling rate of ~0.5–1.0°C/s. The fine-crystal charge (F charge) in the form of thin ingots weighing 0.2–0.3 kg is obtained by crystallization of the melt in cast-iron cold molds with ~5.0–10°C/s. Further, the charge billets are separately melted, re-refined and degassed, and the samples are poured to determine the gas content and density in the liquid (dL) and solid (dS) states. It is established that structural information from the original charge of the alloy is stable in the solid–liquid–solid system. Direct thermal analysis is used to find that the melt obtained from the F charge hardens at low temperatures: the decrease in liquidus temperature tL is 3°C; the temperature of the beginning of solidification of the eutectic is reduced by 10°C, and the temperature of the end of solidification of a eutectic is 3°C in comparison with the melt of the C charge. At the same time, the formation of α-Al and eutectic dendrites in the melt from the F charge occurs 0.4 and 0.6 min more quickly, respectively. The results obtained on the Paraboloid-4 installation show that a smaller number of pulses throughout the studied temperature range passes through the melt from the F charge, which confirms its increased density when compared to the alloy from the C charge. Thus, for the melt from the F charge, the values of the degrees of compaction were –ΔJl ~ 278.66 and –ΔJe ~ 129.83 imp/s and, for the melt from the C charge, –ΔJl ~ 302.9 and –ΔJe ~ 163.47 imp/s. The values of the phase-transition temperatures determined by anomalies on the temperature dependence Jt practically coincide with the results of direct thermal analysis. The main technological recommendations of management by structural information in aluminum alloys are formulated from the position of the phenomenon of structural heredity.

CF4 plasma-fluorinated nano-SiC promotes the charge transfer in the interface of epoxy nanocomposites

Insulation failure and surface flashover of nanocomposites insulator caused by charge accumulation remain to be major hurdles in the application of high voltage equipment. In this study, we develop a plasma fluorination treatment method to graft fluorinated functional groups onto the surface of nano-SiC, in order to change the interfacial characteristics of the nanocomposites and promote charge transfer. Surface potential measurement and volume conductivity measurement are performed to evaluate charge transfer in the nanocomposites. When the concentration of fluorinated nano-SiC is 5 wt.%, the surface decay rate of the sample is larger than that of samples doped with less nanofiller, and the initial surface charge density is 79.8% that of the undoped sample. Furthermore, the fluorinated nano-SiC/epoxy nanocomposites show larger volume conductivity because of the introduction of CF3 functional groups, which influences the interfacial characteristics and promotes charge transfer in the interfacial regions of the nanocomposites. This work demonstrates the effect of charge transfer on surface flashover of the nanocomposites and the plasma fluorination treatment of nanoparticles is a novel approach to promote charge transfer and boost surface electrical performance of nanocomposites.

Covalency-Driven Preservation of Local Charge Densities in a Metal-to-Ligand Charge-Transfer Excited Iron Photosensitizer.

Covalency is found to even out charge separation after photo‐oxidation of the metal center in the metal‐to‐ligand charge‐transfer state of an iron photosensitizer. The σ‐donation ability of the ligands compensates for the loss of iron 3d electronic charge, thereby upholding the initial metal charge density and preserving the local noble‐gas configuration. These findings are enabled through element‐specific and orbital‐selective time‐resolved X‐ray absorption spectroscopy at the iron L‐edge. Thus, valence orbital populations around the central metal are directly accessible. In conjunction with density functional theory we conclude that the picture of a localized charge‐separation is inadequate. However, the unpaired spin density provides a suitable representation of the electron–hole pair associated with the electron‐transfer process.

Observation of Many-Body Localization in a One-Dimensional System with a Single-Particle Mobility Edge.

We experimentally study many-body localization (MBL) with ultracold atoms in a weak one-dimensional quasiperiodic potential, which in the noninteracting limit exhibits an intermediate phase that is characterized by a mobility edge. We measure the time evolution of an initial charge density wave after a quench and analyze the corresponding relaxation exponents. We find clear signatures of MBL when the corresponding noninteracting model is deep in the localized phase. We also critically compare and contrast our results with those from a tight-binding Aubry-André model, which does not exhibit a single-particle intermediate phase, in order to identify signatures of a potential many-body intermediate phase.