Saturation Mechanism Research Articles

Molecular mechanism of hydrophobic tail chain saturation in nonionic surfactants changing the wettability of anthracite

Coal dust is a significant issue when it comes to the safety of coal mine operations. To create efficient surfactants for coal dust, it is crucial to comprehend the molecular principles governing the interactions between surfactants, water, and coal. In this investigation, the macromolecular model of anthracite was constructed. Polysorbate 60 (T60) and Polysorbate 80 (T80) were selected. First, using contact angle measurements, Fourier transform infrared spectroscopy (FTIR) experiment, and Wetting heat measurements, we contrasted how T60 and T80 affected the wettability of coal surfaces. Second, the causes for the various abilities of T60 and T80 were described from a microscopic perspective using molecular dynamics simulation, by evaluating mean square displacement (MSD), mass density, hydrophobic tail chain sequence parameters, interaction energy. According to the findings, T80 has a superior wetting impact on anthracite because it increases the coal surface's polarity and enhances its capacity to bind water molecules; The unsaturated double bond in T80 limited the free expansion of its hydrophobic tail, but following adsorption to the surface of anthracite, it expanded, resulting in a denser and more concentrated layered structure.

Staircase formation by resonant and non-resonant transport of potential vorticity

The E × B staircase is a quasi-periodic pattern of pressure profile corrugations. In this work, we present a new mechanism for E × B staircase formation that involves resonant transport versus non-resonant transport. We start from a potential vorticity evolution system and use quasi-linear theory, a model dispersion relation, and a bi-Lorentzian spectrum approximation, to construct the relation between the fluxes and the profiles. With these fluxes, we close the profile evolution equations and the extended turbulence intensity evolution equation, which together constitute a turbulence-profile evolution system. In this system, the Doppler effect from the E × B mean flow can cause resonance between trapped ion precession motion and the trapped ion mode, which drives a resonant transport contribution to the fluxes. The profiles will be flattened where the resonant transport is switched on. In contrast, for the regions of non-resonant transport, profiles are steeper. A quasi-periodic pattern of profile corrugation (the E × B staircase) spontaneously emerges in this system, which is the two states mentioned above, arranged as alternating layers in space. The feedback processes during the staircase pattern formation are identified. An estimate of the critical value of the boundary heat flux is obtained, above which the staircase formation will be triggered. An estimate scaling of the step size in the staircase pattern is obtained. The resonant turbulent transport is also a mechanism for collisionless saturation of zonal flow. This work is related to internal transport barrier formation and suggests some new scenarios, such as an enhanced confined L mode.

Global E × B flow pattern formation and saturation

The E × B flow staircase-like pattern observed in the first principle gyrokinetic numerical experiments of tokamak fusion plasmas forms due to a nonlinear time delay. Simulations demonstrate a finite time delay between the staircase occurrence in particle transport and that in the density profile. This novel finding shows that instability can arise from perturbations in transport and then influence the background turbulence. E × B flow staircase plays roles not only in shearing the transport but also as a nonlinear saturation mechanism of staircase instability. Experimental measurements in KSTAR tokamak L-mode plasmas are consistent with the numerical findings.

Global gyrokinetic simulations of electrostatic microturbulent transport using kinetic electrons in LHD stellarator

Global gyrokinetic simulations of ion temperature gradient (ITG) and trapped electron mode (TEM) in the LHD stellarator are carried out using the gyrokinetic toroidal code (GTC) with kinetic electrons. ITG simulations show that kinetic electron effects increase the growth rate by more than 50% and more than double the turbulent transport levels compared with simulations using adiabatic electrons. Zonal flow dominates the saturation mechanism in the ITG turbulence. Nonlinear simulations of the TEM turbulence show that the main saturation mechanism is not the zonal flow but the inverse cascade of high to low toroidal harmonics. Further nonlinear simulations with various pressure profiles indicate that the ITG turbulence is more effective in driving heat conductivity whereas the TEM turbulence is more effective for particle diffusivity.

Coupling between conduction and near-field radiative heat transfer in tip–plane geometry

We analyze the coupling between conduction and radiative heat transfer in the near-field regime between two coaxial cylinders separated by a vacuum gap. By solving the heat transport equation in the steady-state regime between metals or polar materials, we highlight a flux saturation mechanism for the radiative transfer even without a non-local effect. In the case of polar materials, this saturation occurs in the separation distances in the range of 1–10 nm, which can be experimentally explored.

Dynamics of homogeneous cavitation with pressure feedback

Theoretical studies of homogeneous cavitation have largely been based on the classical nucleation theory. However, existing cavitation models cannot adequately describe its dynamics at nanosecond timescale, which has been called for in other fields. We develop a model coupling nucleation kinetics with cavity growth and pressure feedback as saturation mechanisms. Our numerical studies reveal the exponential dependence of cavitation characteristics such as saturation cavity density and most probable cavity radius on model parameters: Tolman length and initial pressure. This work also sheds light on the possibility of accurately determining Tolman length, whose value has a large spread in the literature.

On the Efficiency Enhancement of an Actively Tunable MEMS Energy Harvesting Device

In this paper, we propose an active control method to adjust the resonance frequency of a capacitive energy harvester. To this end, the resonance frequency of the harvester is tuned using an electrostatic force, which is actively controlled by a voltage source. The spring softening effect of the electrostatic force is used to accommodate the dominant frequency of the ambient mechanical vibration within the bandwidth of the resonance region. A single degree of freedom is considered, and the nonlinear equation of motion is numerically integrated over time. Using a conventional proportional–integral–derivative (PID) control mechanism, the results demonstrated that our controller could shift the resonance frequency leftward on the frequency domain and, as a result, improve the efficiency of the energy harvester, provided that the excitation frequency is lower than the resonance frequency of the energy harvester. Application of the PID controller in the resonance zone resulted in pull-in instability, adversely affecting the harvester’s performance. To tackle this problem, we embedded a saturation mechanism in the path of the control signal to prevent a sudden change in motion amplitude. Outside the pull-in band, the saturation of the control signal resulted in the reduction of harvested power compared to the non-saturated signal; this is a promising improvement in the design and analysis of energy harvesting devices.

Pharmacokinetics and tissue distribution of deferoxamine-based nanochelator in rats.

Aim: To characterize the pharmacokinetics of deferoxamine-conjugated nanoparticles (DFO-NPs), a novel nanochelator for removing excess iron. Materials & methods: The pharmacokinetics of DFO-NPs were evaluated in Sprague-Dawley rats at three doses (3.3, 10and 30μmol/kg) after intravenous and subcutaneousadministration. Results: DFO-NPs exhibited a biphasic concentration-time profile after intravenous administration with a short terminal half-life (2.0-3.2h), dose-dependent clearance (0.111-0.179 l/h/kg), minimal tissue distributionand exclusive renal excretion with a possible saturable reabsorption mechanism. DFO-NPs after subcutaneous administration exhibited absorption-rate-limited kinetics with a prolonged half-life (5.7-10.1h) and favorable bioavailability (47-107%). Conclusion: DFO-NPs exhibitnonlinear pharmacokinetics with increasing dose, and subcutaneous administration substantially improves drug exposure, thereby making it a clinically viable administration route for iron chelation.

Bubble nuclei: Single-particle versus Coulomb interaction effects

The detailed investigation of microscopic mechanisms leading to the formation of bubble structures in nuclei is performed in the framework of covariant density functional theory. The main emphasis of this study is on the role of single-particle degrees of freedom and Coulomb interaction. In general, the formation of bubbles lowers the Coulomb energy. However, in nuclei this trend is counteracted by the quantum nature of the single-particle states: only specific single-particle states with specific density profiles can be occupied with increasing proton and neutron numbers. A significant role of the central classically forbidden region at the bottom of the wine bottle potentials in the formation of nuclear bubbles (via primarily the reduction of the densities of the $s$ states at $r=0$) is revealed for the first time. Their formation also depends on the availability of low-$l$ single-particle states for occupation since single-particle densities represent the basic building blocks of total densities. Nucleonic potentials disfavor the occupation of such states in hyperheavy nuclei and this contributes to the formation of bubbles in such nuclei. Existing bubble indicators are strongly affected by single-particle properties and thus they cannot be reliable measures of bulk properties (such as the Coulomb interaction). An additivity rule for densities is proposed for the first time. It was shown that the differences in the densities of bubble and flat density nuclei follow this rule in the $A\ensuremath{\approx}40$ mass region and in superheavy nuclei with comparable accuracy. This strongly suggests the same mechanism of the formation of central depression in bubble nuclei of these two mass regions. Nuclear saturation mechanisms and self-consistency effects also affect the formation of bubble structures. The detailed analysis of different aspects of bubble physics strongly suggests that the formation of bubble structures in superheavy nuclei is dominated by single-particle effects. The role of the Coulomb interaction increases in hyperheavy nuclei but even for such systems we do not find strong arguments that the formation of bubble structures is dominated by it.

A Novel Mesh‐Based Equivalent Magnetic Network for Deep Saturation Region of Permanent Magnet Machine

AbstractPartial deep saturation of magnetic circuit is common in short‐term working permanent magnet (PM) machines in aviation, aerospace, new energy power generation and other fields. In order to accurately calculate the electromagnetic characteristics of the short‐term working machine, a novel mesh‐based equivalent magnetic network for the deep saturation region is proposed. Firstly, the deep saturation mechanism of the magnetic circuit of short‐term working motor is analyzed, and the deep saturation region is determined; Secondly, a Pointy topped hexagonal segmentation approach (PT‐HSA) grid generation method is proposed to effectively simulate complex magnetic flux paths. The PT‐HSA grid division and node compilation rules were analyzed in detail. In addition, a nonlinear magnetic network model based on reluctance grid model and equivalent magnetic circuit model is established. Compared with the quadrilateral segmentation approach (QSA) model, the calculation results of PT‐HSA model are closer to the finite element simulation results in the loading and instantaneous compensation conditions. Finally, an experimental platform is built, and the accuracy of the PT‐HSA magnetic network model is verified by the experimental results. © 2022 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

An AC Fault Ride Through Method for MMC-HVDC System in Offshore Applications Including DC Current-Limiting Inductors

The current-limiting inductors (CLIs) are commonly used to suppress DC fault current to safely trip DC circuit breakers in MMC-HVDC systems, but it significantly jeopardizes DC dynamics and causes instantaneous power mismatch between AC and DC sides of islanded rectifier station (RS), exposing MMC internal states to large disturbance. This paper firstly provides a detailed analysis of the influence of CLIs on AC fault, establishes RS mathematical representation including AC side dynamic, and reveals the mechanism of DC voltage oscillation, modulation saturation and PCC waveform distortion. The analysis shows that the AC and DC fault characteristics are decoupled under unsaturated AC modulation, but coupled under excessively low submodule capacitor voltage, where AC modulation is saturated and PCC waveforms are distorted. To solve this issue, a novel RS AC fault ride through method for MMC-HVDC system with CLIs is proposed to stabilize RS DC voltage, desaturate AC modulation and decouple fault characteristics by regulating the zero-sequence modulation of circulating current suppression. In addition, a current reference disturbance and an AC energy dissipation device coordinated control are designed, which adaptively recovers the submodule capacitor voltage. Finally, the feasibility of the proposed method is verified by simulation results.

Proportional–Integral Observer Design for Uncertain Time-Delay Systems Subject to Deception Attacks: An Outlier-Resistant Approach

This article deals with the proportional–integral observer (PIO) design problem for a class of linear systems with distributed time delays and randomly occurring parameter uncertainties. The measurement signals, transmitted from the sensors to the observer, might suffer from the randomly occurring deception attacks. The random occurrences of parameter uncertainties and deception attacks are governed by two series of Bernoulli random variables with known probability distributions. An outlier-resistant PIO is developed by introducing an innovation saturation mechanism for the sake of alleviating the adverse effects induced by the deception attacks on the estimation performance. The purpose of the addressed problem is to design a PIO that is capable of guaranteeing the mean-square boundedness of the estimation errors while achieving the desired security level. The desired PIO gain is designed by solving a matrix inequality and the validity of the results obtained is shown by a numerical simulation example.

Saturation control for fuzzy markovian switching systems with singularly perturbation and cyber-attacks

This paper is concerned with the issue of saturation control for discrete-time fuzzy Markov switching singularly perturbed systems. To describe the dynamic stochastic jumping behavior of system states, a novel nonhomogeneous Markov process is proposed, whose time-varying transition probabilities are orchestrated by a higher-level deterministic switching signal. Additionally, a novel control law is built by considering the random occurrence of cyber-attacks, and cyber-attacks rates are uncertain. Meanwhile, the saturation mechanism is adopted in designing an asynchronous controller, which is capable of eliminating the impact of cyber-attacks to a certain extent. In the end, two simulation results are provided to verify the effectiveness of the proposed methodology.

X-ray emission of contact binary variables within 1 kpc

Aims. The X-ray emission of contact binaries (EW-type) is an important facet of such systems. Thus, X-ray emitting EW-type binaries (EWXs) are ideal laboratories for studying the X-ray radiation saturation mechanisms as well as binary evolution. By assembling the largest sample to date of EWXs with periods of less than 1 day from the All-Sky Automated Survey for Supernovae Variable Stars Database and X-ray catalogs from the XMM-Newton and ROSAT missions, we aim to conduct a systematic population study of X-ray emission properties of EWXs within 1 kpc. Methods. We carried out correlation analyses for the X-ray luminosity, log LX, and X-ray activity level log(LX/Lbol) versus the orbital period, P, effective temperature, Teff, metallicity [Fe/H], and the surface gravity log g of EWXs. We investigated the relation between X-ray emission and the mass of component stars in the binary systems. We also performed sample simulations to explore the degeneracy between period, mass, and effective temperature for EWXs. Results. We find strong P–log LX and P–log(LX/Lbol) correlations for EWXs with P ≲ 0.44 days and we provide the linear parametrizations for these relations, on the basis of which the orbital period can be treated as a good predictor for log LX and log(LX/Lbol). The aforementioned binary stellar parameters are all correlated with log LX, while only Teff exhibits a strong correlation with log(LX/Lbol). Then, EWXs with higher temperature show lower X-ray activity level, which could indicate the thinning of the convective area related to the magnetic dynamo mechanism. The total X-ray luminosity of an EWX is essentially consistent with that of an X-ray saturated main sequence star with the same mass as its primary, which may imply that the primary star dominates the X-ray emission. The monotonically decreasing P–log(LX/Lbol) relation and the short orbital periods indicate that EWXs could all be in the X-ray saturated state, and they may inherit the changing trend of the saturated X-ray luminosities along with the mass shown by single stars. For EWXs, the orbital period, mass, and effective temperature increase in concordance. We demonstrate that the period P = 0.44 days corresponds to the primary mass of ∼1.1 M⊙, beyond which the saturated X-ray luminosity of single stars will not continue to increase with mass. This explains the break in the positive P–log LX relation for EWXs with P > 0.44 days.

Hybrid Zakharov-kinetic simulation of nonlinear stimulated Raman scattering

We present a novel 2D reduced numerical model for stimulated Raman scattering (SRS) in laser fusion plasmas in which envelope equations for the electromagnetic fields are coupled to a hybrid description of the electron species. Specifically, the electron distribution is split between a bulk part described by a Zakharov-like linear model and a kinetic tail discretized using a particle-in-cell-like (PIC) scheme. By avoiding to sample the bulk-electron distribution, this approach greatly reduces the numerical cost of SRS simulations compared with PIC codes, while still being able to describe the nonlinear evolution of the electron tail and trapping-related kinetic phenomena. First, our model is shown to reproduce accurately the linear Landau damping of an infinitesimal electron plasma wave (EPW) whose phase velocity falls into the tail of the electron distribution. Then, applying it to the simulation of the trapped-particle modulational instability of a large-amplitude EPW, results comparable to those of previously published 2D Vlasov simulations are obtained. Finally, we simulate the excitation of kinetic backward SRS from a single strong laser speckle (λ=0.527 μm, I=1016 W cm−2) in an underdense (ne=0.036 nc) plasma, which drives an EPW with wavenumber kλD≈0.34. The model predictions fairly agree with the results of a PIC simulation regarding the kinetic saturation mechanisms (i.e., trapped-particle instabilities), and with experimental data and Vlasov simulations related to the frequency shift of nonlinear EPWs. For this SRS simulation, we estimate that our hybrid model is over an order of magnitude less costly than an equivalent PIC simulation due to the lower particle count.

The Effect of the Water Table on the Bearing Capacity of a Shallow Foundation

Immersion is an important part of reservoir engineering investigation and evaluation. Determining the reasonable and effective burial depth of the critical immersion water table is one of the key scientific issues in the impact assessment of the bearing capacity of reservoir immersion foundations. In this study, basic physical and mechanical property tests were carried out on the soil in the typical immersion area of Xiaonanhai Hydropower Station, and the influence mechanism of saturation on the mechanical properties of building foundation soil and immersion on the bearing capacity of a shallow foundation was obtained. According to the test results, the influence depth of the rising groundwater level on the stability of the building foundation is analyzed, and a method to determine the critical depth of immersion groundwater in the reservoir is proposed. Taking the typical building foundation of Luohuang Town in the immersion area of Xiaonanhai Reservoir as an example, the validity of the critical water depth is further verified. The results show that the safety limit depth of the independent foundation affected by the rise of the water table increases with the increase of the width of the foundation and decreases with the increase of the buried depth of the foundation. Considering the safety limit depth, the critical depth of building immersion is 4.830 m, and without considering the safety limit depth, the critical depth of building immersion is 4.05 m. To a certain extent, it can reduce the impact of water table changes on the bearing capacity of shallow foundations.

Experiments on the dynamics and scaling of spontaneous-magnetic-field saturation in laser-produced plasmas.

In laser-produced high-energy-density plasmas, large-scale strong magnetic fields are spontaneously generated by the Biermann battery effects when temperature and density gradients are misaligned. Saturation of the magnetic field takes place when convection and dissipation balance field generation. While theoretical and numerical modeling provide useful insight into the saturation mechanisms, experimental demonstration remains elusive. In this letter, we report an experiment on the saturation dynamics and scaling of Biermann battery magnetic field in the regime where plasma convection dominates. With time-gated charged-particle radiography and time-resolved Thomson scattering, the field structure and evolution as well as corresponding plasma conditions are measured. In these conditions, the spatially resolved magnetic fields are reconstructed, leading to a picture of field saturation with a scaling of B∼1/L_{T} for a convectively dominated plasma, a regime where the temperature gradient scale (L_{T}) exceeds the ion skin depth.

Optimal rectangular crack pattern based on constructal, fracture saturation, and energy minimization theories for painting on wood

The knowledge of how the craquelure happens and their pattern on historical objects especially paintings are interested in the field of cultural heritage. In this paper, optimal rectangular patterns are calculated based on current theories for a fully anisotropic model of wood and an anisotropic model of gesso annealing shrinkage. First, the constructal theory is applied which is responsible for the crack growth at the beginning periods of drying the produced painting. As the constructal theory is based on greater access to the drying currents that flow through the crack pattern, the compromise of two mechanisms of diffusion of moisture content and advection drying by fluid flow through the cracks detect the optimal scale of rectangular patterns. A rectangular two-dimensional solid is dried by the diffusion mechanism and advection boundary condition. The resulted shape is found by the intersection of two limits of many cracks (dense crack by high advection) versus a few cracks analytically. Then a parametric study is done to find the optimal distance between blocks of crack islands numerically. Second, the fracture saturation mechanism in long-term climate changes is applied to find the possible rectangular pattern which can appear based on the fact that positive stress should exist in the middle of the crack island to create a new crack. Finally, the strain energy density approach for various fracture strengths is examined to predict the optimal rectangular shape. The numerical results are compared with existing experimental results and previous works demonstrate the capability of the above-mentioned models. The method and results could be generalized for the other types of craquelure patterns and structural conservators.

Multivariable phase-locked loop free strategy for power control of grid-connected voltage source converters

A multivariable control strategy in a dq reference frame for grid-connected voltage source converters (VSCs) without using a phase-locked loop (PLL) is presented in this paper. First, common VSC controls such as vector current control (VCC) and grid voltage modulated direct power control (GVM-DPC) are analyzed and their main drawbacks are identified. Then, the multivariable control strategy is presented, including the implementation of saturation and anti-windup mechanisms, and limitation of overcurrents. Next, different uncertainty channels that may lead to instability in each approach are analyzed, showing the drawbacks related to the use of a PLL, which are avoided in our proposal. The effectiveness of the three strategies is compared by means of MATLAB/Simulink simulations, showing that the proposal presents a more robust behavior, specially in weak grids.

Small Extracellular Vesicles in Milk Cross the Blood-Brain Barrier in Murine Cerebral Cortex Endothelial Cells and Promote Dendritic Complexity in the Hippocampus and Brain Function in C57BL/6J Mice.

Human milk contains large amounts of small extracellular vesicles (sEVs) and their microRNA cargos, whereas infant formulas contain only trace amounts of sEVs and microRNAs. We assessed the transport of sEVs across the blood-brain barrier (BBB) and sEV accumulation in distinct regions of the brain in brain endothelial cells and suckling mice. We further assessed sEV-dependent gene expression profiles and effects on the dendritic complexity of hippocampal granule cells and phenotypes of EV depletion in neonate, juvenile and adult mice. The transfer of sEVs across the BBB was assessed by using fluorophore-labeled bovine sEVs in brain endothelial bEnd.3 monolayers and dual chamber systems, and in wild-type newborn pups fostered to sEV and cargo tracking (ECT) dams that express sEVs labeled with a CD63-eGFP fusion protein for subsequent analysis by serial two-photon tomography and staining with anti-eGFP antibodies. Effects of EVs on gene expression and dendritic architecture of granule cells was analyzed in hippocampi from juvenile mice fed sEV and RNA-depleted (ERD) and sEV and RNA-sufficient (ERS) diets by using RNA-sequencing analysis and Golgi-Cox staining followed by integrated neuronal tracing and morphological analysis of neuronal dendrites, respectively. Spatial learning and severity of kainic acid-induced seizures were assessed in mice fed ERD and ERS diets. bEnd.3 cells internalized sEVs by using a saturable transport mechanism and secreted miR-34a across the basal membrane. sEVs penetrated the entire brain in fostering experiments; major regions of accumulation included the hippocampus, cortex and cerebellum. Two hundred ninety-five genes were differentially expressed in hippocampi from mice fed ERD and ERS diets; high-confidence gene networks included pathways implicated in axon guidance and calcium signaling. Juvenile pups fed the ERD diet had reduced dendritic complexity of dentate granule cells in the hippocampus, scored nine-fold lower in the Barnes maze test of spatial learning and memory, and the severity of seizures was 5-fold higher following kainic acid administration in adult mice fed the ERD diet compared to mice fed the ERS diet. We conclude that sEVs cross the BBB and contribute toward optimal neuronal development, spatial learning and memory, and resistance to kainic acid-induced seizures in mice.