Onset Of Breakdown Research Articles

Concurrent geometrico-topological tuning of nanoengineered auxetic lattices fabricated by material extrusion for enhancing multifunctionality: Multiscale experiments, finite element modeling and data-driven prediction

This study demonstrates the multifunctional performance of innovative 2D auxetic lattices through a combination of multiscale experiments, finite element modeling and data-driven prediction. A geometric modeling approach utilizing Voronoi partitioning and a unique branch-stem-branch (BSB) structure, patterned according to 2D wallpaper symmetries, enables precise concurrent geometric and topological tuning of lattices across a continuous parameter space. Selected architectures are physically realized via material extrusion of polylactic acid (PLA) infused with carbon black (CB). Experimental characterizations, supported by Finite Element modeling, reveal the significant influence of BSB structure's design parameters on mechanical and piezoresistive performance under tensile loading, with a remarkable Poisson’s ratio of -0.74, accompanied by a 15-fold increase in elastic stiffness and a 34-fold increase in strain sensitivity. Additionally, architecturally, and topologically tailored lattice structures exhibit tunable damage sensitivity, reflecting the rate of conductive network destruction within the lattice. This offers insights into the rapidity of cell wall failure, with a steeper slope of the piezoresistance curve in the inelastic regime indicating a faster breakdown and quicker onset of mechanical failure. Integration of Gaussian Process Regression enables accurate exploration of the design space beyond realized structures, highlighting the potential of these intelligent lattice structures for applications such as sensors and in situ health monitoring, marking a significant advancement in multifunctional materials.

Unintended gas breakdowns in narrow gaps of advanced plasma sources for semiconductor fabrication industry

Occurrence of unintended gas breakdown in the narrow gaps of plasma processing chambers is one of the critical challenges in developing advanced plasma sources. We present a combined experimental and theoretical study of unintended discharges in the narrow gaps of plasma processing chambers and report significant drop of the gas breakdown voltage in the presence of a background plasma facing the gap. Experimentally measured breakdown voltages decrease in subsequent breakdown events due to wall erosion caused by the discharge. Therefore, preventing and mitigating the first discharge is of paramount importance. An analysis of kinetic simulation results indicates that the charged particle influx from the background plasma in the processing chamber into the gap is responsible for the onset of early breakdown: higher charged particle density within the gap modifies the electric field profile, allowing unintended breakdowns to occur at a significantly reduced threshold voltage.

Habitat fragmentation affects climate adaptation in a forest herb

Abstract Climate change and the resulting increased drought frequencies pose considerable threats to forest herb populations, particularly where additional environmental challenges jeopardize responses to selection. Specifically, habitat fragmentation may hamper climate adaptation by altering the distribution of adaptive genetic variation and may also induce evolutionary changes in mating systems. To assess how habitat fragmentation disrupts climate adaptation, we conducted a common garden experiment with Primula elatior offspring originating from 24 populations sampled along a latitudinal gradient with varying climate and landscape characteristics. We then quantified a range of vegetative, regulatory and reproductive traits under distinct soil moisture regimes to evaluate imprints of local adaptation and phenotypic plasticity. Additionally, we conducted a more extensive field campaign in 60 populations along the same latitudinal gradient to evaluate the potential evolutionary breakdown of reciprocal herkogamy. For large, connected populations, our results demonstrated an evolutionary shift from a strategy in southern populations that seems aligned with drought avoidance—where plants minimize their exposure to dry conditions and optimize photosynthesis—to a drought tolerance strategy in northern populations, where plants are adapted to function despite water scarcity. However, habitat fragmentation disrupted climate clines and the adaptive responses to drought stress in key traits related to growth, biomass allocation and water regulation. Additionally, our findings indicate the onset of evolutionary breakdown in reciprocal herkogamy and divergence in other key flower traits. The disruption of climate clines, drought responses and adaptations in mating systems contributed to a substantially diminished flowering investment across the distribution range, with the most pronounced effects observed in southern fragmented populations. Synthesis. We present novel empirical evidence of how habitat fragmentation disrupts climate adaptation and drought tolerance in a wide range of traits along the range of the forest herb Primula elatior. These findings emphasize the need to account for habitat fragmentation while designing effective conservation strategies in order to preserve and restore resilient meta‐populations of forest herbs amidst ongoing global changes.

Modulating the chiral nematic structure of cellulose nanocrystal suspensions with electrolytes

HypothesisThe iridescent optical properties of films made of cellulose nanocrystals (CNC) are controlled by the pitch and range of the chiral nematic structures. These are further tuned with the addition of electrolyte. ExperimentsElectrolyte type, valency and concentration were varied. The bulk CNC suspension properties were investigated by combining rheology, polarised optical photography and microscopy, while the spacing between crystals was determined using SAXS. FindingsThe addition of electrolyte to a CNC suspension containing chiral nematic structures first causes the nematic pitch to increase indicating the suspension has a weaker structure. Further increases in electrolyte concentration cause aggregation and complete breakdown of the chiral nematic structures. The univalent species cause larger changes to the chiral nematic structure with the onset and magnitude of structure breakdown occurring at lower ionic strengths compared with the divalent species. Cation size influences the chiral nematic structure with the order of influence being K+ > Na+ ≈ Ca2+ > Mg2+, which corresponds from the largest to smallest cation. This work demonstrates that both ion valency, concentration and species play a significant role in controlling the chiral nematic structures of CNC suspensions and will be a vital step in the development of CNC liquid crystals, optical materials and sensors.

Modeling and simulation of a helical falling film evaporator to improve its performance and design

This work presents a computational model of a helical falling film evaporator of 13 tubes based on physical principles. The momentum and energy transfer of the system are modeled. The work aims to understand the behavior of a horizontal falling film evaporator and to improve the evaporator design by analyzing the heat transfer. In the evaporator, the wetting efficiency varies in each tube because the evaporation of the falling film is performed gradually. Therefore, the behavior of the evaporator variables, such as the wetting efficiency in each tube, is studied. Furthermore, the model granularity based on the analysis of the subcooling and saturation zones is investigated. The effect of the film breakdown onset Reynolds number and the mass flow rate on the evaporator performance is studied. This analysis shows that the maximum heat transfer rate of the simulation is reached when the falling film Reynolds numbers of the tubes are as close as possible and pass by the film breakdown onset Reynolds number value. Additionally, the results indicate that at a low mass flow rate, the heat transfer is carried out almost completely in the first five tubes, and at a higher mass flow rate, the heat transfer is more significant in the last tubes. Finally, a comparison between the evaporator of 13 tubes and an arrangement of two evaporators of five tubes each one is performed. From this analysis, the results show that the heat transfer rate of the arrangement of two evaporators is 21.16 % and 18.69 % higher than the evaporator of 13 tubes at 0.00529 and 0.00793 kg/s⋅m, respectively.

Enhancement of traffic management algorithms for UK motorways

The overall aim of this work is to review and improve traffic CM algorithm to delay the onset of flow breakdown. The results indicated that compared to other two classic models, the Underwood model was able to match the field data on the M25 motorway consistently and capture the speed-flow relationships successfully, in terms of larger R-squared coefficient (R2) and smaller average values of root mean squared error (RMSE). In addition, it was found that Gaussian function can describe the relationship between flow values at the turning points of traffic speed and flow curve and the threshold of the CM algorithm. The fitted traffic speed and flow curve showed that the values at the turning points were significantly reduced under light and heavy rainfall. Thus, the threshold values of the CM algorithm should be optimized according to the determined Gaussian function in the present work.

Film breakdown onset Reynolds number of an absorption heat transformer with falling film heat exchangers: Modeling and estimation

This work presents the development of a physical model for an absorption heat transformer with falling film heat exchangers. The absorption heat transformers are devices for increasing moderate temperatures of heat sources to more useful levels to be used in some processes as water purification. The process units are modeled in lumped form to reduce the model complexity. The phenomena that appear in the falling film heat transfer are analyzed. The laminar flow with partial wetting describes the behavior of the units. The falling film reaches full wetting efficiency at the film breakdown onset Reynolds number, which is considered a parameter. Sensitivity analysis is applied to the AHT model to identify the sensible variables that are affected by the film breakdown onset Reynolds number of each unit, then these parameters are estimated. The film breakdown onset Reynolds number estimated for the units are from 8.90 to 141.28, which depend on the unit geometries, the fluid properties, and the physical phenomenon. The evaporator lumped model of the process of this work is compared with a detailed evaporator model specific regarding each round of coil presented in previous research. From this comparison, it is recommended to model the first tube of the evaporator individually while the other tubes can be modeled in lumped form. The model results are compared with experimental results to validate the model. The comparison shows low errors from 0.22 to 6.13 %, except for the pressure of the evaporator–absorber chamber with an error of 13.83 %. Finally, some tests at different generator temperatures varying the cooling water temperature from 33.8 °C to 31.8 °C decrease the pressure by approximately 0.53 kPa and increase the flow of refrigerant by 0.00011 kg/s. The establishment of the model and the estimation of the unknown parameters would contribute to the development of accurate dynamic models for absorption heat transformers to implement strategies to improve control process.

On the Onset of Breakdown of the Virtual Gate in AlGaN/GaN HEMTs

On the Onset of Breakdown of the Virtual Gate in AlGaN/GaN HEMTs

Structure disorder observation of fluoropolymers composed of vinylidene fluoride and tetrafluoroethylene in supercritical CO2 using time-resolved small- and wide-angle X-ray scattering

Fluoropolymers have a growing range of applications in many industries. Neat fluoropolymers and fluorinated copolymers were prepared via the suspension polymerization method with entire mass ratio of vinylidene fluoride (VdF) and tetrafluoroethylene (TFE). Supercritical CO2 was applied as a fluid stimulus to the fluoropolymers. An increase in structural disorder was investigated using time-resolved small-angle X-ray scattering (SAXS). The SAXS change induced by the stimulus proceeded more slowly with increasing VdF ratio of the copolymer, suggesting that the higher VdF content contributes to the tolerance of microvoid formation and the corresponding onset of breakdown in the polymer material. The degree of crystallinity of the fluoropolymers was evaluated using wide-angle X-ray scattering, showing the degree of crystallinity was similar before and after the stimulus. Time-resolved and in-situ SAXS/WAXS measurements were carried out on the copolymer with a ratio of VdF:TFE = 8:2 as the copolymer having the highest VdF content studied here.

Shared Molecular Mechanisms among Alzheimer's Disease, Neurovascular Unit Dysfunction and Vascular Risk Factors: A Narrative Review.

Alzheimer’s disease (AD) is the most common type of dementia, affecting 24 million individuals. Clinical and epidemiological studies have found several links between vascular risk factors (VRF), neurovascular unit dysfunction (NVUd), blood-brain barrier breakdown (BBBb) and AD onset and progression in adulthood, suggesting a pathogenetic continuum between AD and vascular dementia. Shared pathways between AD, VRF, and NVUd/BBB have also been found at the molecular level, underlining the strength of this association. The present paper reviewed the literature describing commonly shared molecular pathways between adult-onset AD, VRF, and NVUd/BBBb. Current evidence suggests that VRF and NVUd/BBBb are involved in AD neurovascular and neurodegenerative pathology and share several molecular pathways. This is strongly supportive of the hypothesis that the presence of VRF can at least facilitate AD onset and progression through several mechanisms, including NVUd/BBBb. Moreover, vascular disease and several comorbidities may have a cumulative effect on VRF and worsen the clinical manifestations of AD. Early detection and correction of VRF and vascular disease by improving NVUd/BBBd could be a potential target to reduce the overall incidence and delay cognitive impairment in AD.

Vortex breakdown in variable-density gaseous swirling jets

Theoretical predictions and numerical simulations are used to determine the transition to bubble and conical vortex breakdown in low-Mach-number laminar axisymmetric variable-density swirling jets. A critical value of the swirl number $S$ for the onset of the bubble ( $S^*_B$ ) and the cone ( $S^*_C$ ) is determined as the jet-to-ambient density ratio $\varLambda$ is varied, with the temperature dependence of the gas density and viscosity appropriate to that of air. The criterion of failure of the slender quasi-cylindrical approximation predicts $S^*_B$ that decreases with increasing values of $\varLambda$ for a jet in solid-body rotation emerging sharply into a quiescent atmosphere. In addition, a new criterion for the onset of conical breakdown is derived from divergence of the initial value of the radial spreading rate of the jet occurring at $S^*_C$ , found to be independent of $\varLambda$ , in an asymptotic analysis for small distances from the inlet plane. To maintain stable flow in the unsteady numerical simulations, an effective Reynolds number $Re_{eff}$ , defined employing the geometric mean of the viscosity in the jet and ambient atmosphere, is fixed at $Re_{eff}=200$ for all $\varLambda$ . Similar to the theoretical predictions, numerical calculations of $S^*_B$ decrease monotonically as $\varLambda$ is increased. The critical swirl numbers for the cone, $S^*_C$ , are found to depend strongly on viscous effects; for $\varLambda =1/5$ , the low jet Reynolds number (51) at $Re_{eff}=200$ delays the transition to the cone, while for $\varLambda =5$ at $Re_{eff}=200$ , the large increase in kinematic viscosity in the external fluid produces a similar trend, significantly increasing $S^*_C$ .

Fermi surface and nested magnetic breakdown in WTe2

We report a detailed Shubnikov-de Haas (SdH) study on the Weyl type-II semimetal WTe2 in magnetic fields up to 29 T. By using the SdH results to guide our density functional theory calculations, we are able to accurately determine its Fermi surface by employing a moderate Hubbard U term, which is an essential step in explaining the unusual electronic properties of this much studied material. In addition to the fundamental orbits, we observe magnetic breakdown, which can consistently be explained within the model of a Russian-doll-nested Fermi surface of electron and hole pockets. The onset of magnetic breakdown in WTe2 is solely determined by impurity damping in contrast to magnetic breakdown scenarios in other metallic systems.

Микроканальная структура искрового разряда в промежутке острие-плоскость при различных давлениях воздуха

Using high-speed photography and shadow photography, the structure of the glow and the microstructure of the spark discharge in a 1.5-mm long “pin(cathode)–plane” gap in air in the pressure range from 300 to 760 Torr has been studied. The presence of a microchannel structure of the discharge in the indicated pressure range was established – the discharge is a aggregation of a large number of micron-diameter channels. It is shown that with decreasing pressure, the evolution of the microstructure and glow of the discharge lags behind the onset of breakdown, however, their morphology retains similarity at different pressures.

Microchannel structure of a spark discharge in a pin to plane " gap at different air pressures

Using high-speed photography and shadow photography, the structure of the glow and the microstructure of the spark discharge in a 1.5 mm long "pin(cathode)-plane" gap in air in the pressure range from 300 to 760 Torr has been studied. The presence of a microchannel structure of the discharge in the indicated pressure range was established --- the discharge is a aggregation of a large number of micron-diameter channels. It is shown that with decreasing pressure, the evolution of the microstructure and glow of the discharge lags behind the onset of breakdown, however, their morphology retains similarity at different pressures Keywords: spark discharge, microstructure, method of shadow photography, high-speed shooting.

The measurement and modeling of partial discharges in solid fossil fuels

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels. Keywords: Oil shale, subterranean conversion, field distribution simulation, apparent chage measurement.

Измерение и моделирование частичных разрядов в твердых топливах

The paper is devoted to the study of the characteristics of partial discharges in solid fossil fuels. The appearance of partial discharges in solid fuels occurs at very low voltages, which are not typical for most dielectrics. The activity of partial discharges leads to the onset of rock breakdown. The characteristics of partial discharges in the oil shale of the Huadan deposit (China), presented in the work, indicate the voltage value at which partial discharges arise and breakdown occurs, and also show how these characteristics depend on voltage. We attempted to explain the low value of the voltage of partial discharges in solid fuels, as well as to substantiate the possibility of using partial discharge characteristics to predict the breakdown of the interelectrode space for use in the technology of in-situ heating and the pyrolysis of solid fuels.

Parametric study of cone angle influence on bubble vortex breakdown onset in laminar conical flow at various swirl numbers

The current work studies a swirling laminar viscous pipe flow with a controllable swirl number and varying pipe divergence cone angle. Such flows are widely used in various engineering applications. When a certain level of flow swirl is reached, a phenomenon called vortex breakdown occurs, the characteristics of which depend on the intensity of swirling of the flow and the Reynolds number. However, in addition to these two parameters, an important influence is exerted by the pipe opening angle, which often does not allow generalizing the results obtained in the pipe flow with even slightly different angles. Since experimentally it is quite difficult and expensive to change the pipe angle, especially considering the water as working fluid, this issue could be solved using CFD techniques. Using the design study, 63 different combinations of S and α are considered. The effect of the pipe divergence angle on the position of the bubble vortex breakdown and its properties is demonstrated. It is shown that there is a nonlinear relationship between the position of the bubble breakdown onset and the minimum value of the axial velocity at the axis depending on the opening angle of the cone.

Spectral Measurement of the Breakdown Limit of β−Ga2O3 and Tunnel Ionization of Self-Trapped Excitons and Holes

$\beta-Ga_{2}O_{3}$ is an unusual semiconductor where large electric fields (~1-6 MV/cm) can be applied while still maintaining a dominant excitonic absorption peak below its ultra-wide bandgap. This provides a rare opportunity in the solid-state to examine exciton and carrier self-trapping dynamics in the strong-field limit at steady-state. Under sub-bandgap photon excitation, we observe a field-induced red-shift of the spectral photocurrent peak associated with exciton absorption and threshold-like increase in peak amplitude at high-field associated with self-trapped hole ionization. The field-dependent spectral response is quantitatively fit with an eXciton-modified Franz-Keldysh (XFK) effect model, which includes the electric-field dependent exciton binding energy due to the quadratic Stark effect. A saturation of the spectral red-shift with reverse bias is observed exactly at the onset of dielectric breakdown providing a spectral means to detect and quantify the local electric field and dielectric breakdown behavior. Additionally, the field-dependent responsivity provides insight to the photocurrent production pathway revealing the photocurrent contributions of self-trapped excitons (STXs) and self-trapped holes (STHs). Photocurrent and p-type transport in $\beta-Ga_{2}O_{3}$ are quantitatively explained by field-dependent tunnel ionization of excitons and self-trapped holes. We employ a quantum mechanical model of the field-dependent tunnel ionization of STX and STH to model the non-linear field-dependence of the photocurrent amplitude. Fitting to the data, we estimate an effective mass of valence band holes $(18.8 m_{0})$ and an ultrafast self-trapping time of holes (0.045 fs). This indicates that minority-hole transport in $\beta-Ga_{2}O_{3}$ can only arise through tunnel ionization of STH under strong fields.

Illumination Dependence of Reverse Leakage Current in Silicon Solar Cells

In the modeling of PV modules under shading and low illumination, a complete description of reverse bias behavior at the cell level is critical to understanding module response. This is particularly important when dealing with high voltage configurations such as tandem and shingled modules. Current simulation studies often do not account for the effects of incident light when dealing with operating voltages approaching cell breakdown. In this article, we investigate the illumination dependence of leakage current at the onset of breakdown in crystalline silicon solar cells. A study of the most popular cell technologies in the market today reveals a light induced effect under reverse bias that is prominent for p-type and small for n-type cells. Additionally, this effect is found to be larger in mono c-Si than multi c-Si cells. Because this phenomenon is not captured in current breakdown models such as Bishop's equation, we propose a split-cell model to describe partial shading in p-type cells. The outlined approach divides the cell into two parallel regions and is advantageous for its procedural simplicity as well as its ability to generalize effects from complex shading profiles.

Risk Factors and Outcomes After Surgical Reconstruction of Charcot Neuroarthropathy in Fracture Versus Dislocation Patterns

The primary aim of this study is to compare the preoperative risk factors and postoperative outcomes between Charcot neuroarthropathy patients with dislocation versus purely fracture pattern breakdown. The secondary aim is to compare the same factors between Charcot neuroarthropathy patients with dislocation versus fracture-dislocation pattern breakdown. A total of 55 patients with forefoot, midfoot, or hindfoot Charcot Neuroarthopathy were assessed at a mean follow up of 2.99 years. Bivariate analysis compared preoperative risk factors and postoperative outcomes, and segmented multivariable regression analysis was performed. Dislocation pattern Charcot had statistically significant higher rates of broken hardware (p=.05), mean age (p=.01), and revisional exostectomy (p=.01) compared to pure fracture pattern Charcot. Dislocation pattern Charcot was 12 times more likely to have revisions exostectomy (odds ratio [OR] 12.0, 95% confidence interval [CI] 1.84-78.37), and was 8 times more likely to have osteomyelitis (OR 7.8, 95% CI 1.4-42.7, p=.02) compared to the fracture-dislocation pattern Charcot. The patients with pure fracture pattern Charcot were 58.8 times more likely to have Charcot breakdown involvement of the talonavicular joint compared to the dislocation pattern cohort (OR 58.83, 95% CI 1.1-3220.3). Involvement of the talonavicular joint, in the fracture pattern Charcot associate with medial column collapse occurring at the onset of Charcot breakdown. The dislocation pattern in Charcot Neuroarthropathy demonstrated a higher propensity for residual collapse as demonstrated by the higher rates of broken hardware, osteomyelitis, and need for revisional exostectomy.