Intermittency Effects Research Articles

Gas Transfer Across Air‐Water Interfaces in Inland Waters: From Micro‐Eddies to Super‐Statistics

AbstractIn inland water covering lakes, reservoirs, and ponds, the gas exchange of slightly soluble gases such as carbon dioxide, dimethyl sulfide, methane, or oxygen across a clean and nearly flat air‐water interface is routinely described using a water‐side mean gas transfer velocity , where overline indicates time or ensemble averaging. The micro‐eddy surface renewal model predicts , where is the molecular Schmidt number, is the water kinematic viscosity, and is the waterside mean turbulent kinetic energy dissipation rate at or near the interface. While has been reported across a number of data sets, others report large scatter or variability around this value range. It is shown here that this scatter can be partly explained by high temporal variability in instantaneous around , a mechanism that was not previously considered. As the coefficient of variation in increases, must be adjusted by a multiplier that was derived from a log‐normal model for the probability density function of . Reported variations in with a macro‐scale Reynolds number can also be partly attributed to intermittency effects in . Such intermittency is characterized by the long‐range (i.e., power‐law decay) spatial auto‐correlation function of . That varies with a macro‐scale Reynolds number does not necessarily violate the micro‐eddy model. Instead, it points to a coordination between the macro‐ and micro‐scales arising from the transfer of energy across scales in the energy cascade.

Influence of flame stability on iron oxide nanoparticle growth during FSP

Flame stability during flame spray pyrolysis (FSP) remains an active topic of investigation due to its impact on synthesised particle attributes and purity. The unique feature of the burner investigated here is the ability to control flame stability over newly defined stability maps. The novelty of the current work lies in understanding the influence of these broad stability modes on nanoparticle growth during FSP and on the attributes of collected products. Several distinct flame configurations are selected for iron oxide nanoparticle synthesis, ranging from stable to highly unstable flames. The flame stability regimes are characterised by OH∗ chemiluminescence and broadband flame luminescence imaging. Stability is correlated with the coefficient of variation of flame luminescence (CV) and flame height with mean OH∗ chemiluminescence. Planar Mie scattering is then used to identify the effect of flame luminescence intermittency on spray atomisation and evaporation quality. For particle analysis, in-situ thermophoretic sampling is performed from 30 to 200 mm above the burner exit plane and analysed via transmission electron microscopy (TEM). Further ex-situ analysis is also performed on the bulk-collected product via high-resolution TEM, X-ray powder diffraction (XRD), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). It is demonstrated that flames with higher instability (CVmin ≥ 0.35) maintain increased spray heights (>26 %) and reduced flame heights (>79 %) compared to stable flames with the same precursor volume flowrate. This reduces the high-temperature particle residence time for primary particle growth and impacts subsequent agglomeration. For example, the mean diameter of gyration and primary particle diameter are found to vary by 44 % and 29 % depending on the flame regime, respectively. Ex-situ analysis also demonstrates that the dominant iron oxide phase produced is maghemite regardless of the stability regime. However, higher concentrations of organic impurities including methyl, methylene and carboxylate functional groups are found via ATR-FTIR with increased flame instability (CV).

Modified stochastic diffusion particle-tracking model (MSDPTM) incorporating energy cascade theory and eddy intermittency for suspended sediment transport in open channel flow.

This study presents a modified stochastic diffusion particle tracking model (MSDPTM) that incorporates energy cascade theory to more accurately simulate suspended sediment transport. The impact of turbulent eddies on sediment particles is an intermittent process, which is also considered in this study. The study examines the time correlation between eddies using eddy turnover time and finds that closer-scale eddies exhibit higher correlations than those farther apart. The statistical properties of particle movement, such as the ensemble mean and variance of particle trajectories, have been calculated and compared with the stochastic diffusion particle tracking model (SDPTM) results. Notably, MSDPTM with intermittency demonstrates a significantly larger ensemble mean of particle trajectories in the streamwise direction than other particle tracking models. The proposed model is validated through comparison with available data, showing its enhanced performance. The results of the simulation indicate that MSDPTM outperforms SDPTM, especially when the intermittency effect of eddies is considered.

Plasticity of life-history traits in the Draa barbel <i>Luciobarbus lepineyi</i> (Pellegrin, 1939) (Actinopterygii: Cyprinidae) in the sub-Saharan Draa basin, Morocco: effect of change in flow regime and salinity

The Draa barbel Luciobarbus lepineyi (Pellegrin, 1939), an endemic and unique cyprinid of the arid Draa river basin, southern Morocco, faces a range of multiple environmental stressors, especially in intermittent rivers and ephemeral streams (IRES). We assessed the effects of flow intermittence and salinisation on the somatic condition, and life-history traits in Draa barbels. We used the scaled-mass index (SMi) to evaluate the mean individual somatic body condition in nine populations. For three contrasted localities: Iriri (IR), Mghimima (MG), and Sid El Mokhtar (SM), we aged fish from scales and calculated von Bertalanffy growth parameters using the Beverton-Holt procedure. We used these parameters to estimate growth indices and performance, size and age at maturity, longevity, and mortality rates. Mean SMi decreased markedly with increasing salinity, revealing a normal condition at 0.4 PSU in IR, a poor condition in MG at 4 PSU, and a very poor condition at 10 PSU in SM. Growth rates (k) increased with salinity. Conversely, asymptotic lengths L∞ and growth performances (phi-prime, φ′) decreased with salinity and flow intermittency. The potential longevity tmax decreased with the increase in salinity. On the other hand, the mortality rate increased with flow intermittence and salinity. The Draa barbels in the saline IRES of the arid Draa basin compensate for the high mortality by growing faster but less efficiently. They mature at an earlier age and have shorter longevity. With this high life-history plasticity, the Draa barbel would constitute a good ecological indicator and a sentinel for salinisation in variable aquatic environments in the arid Draa river basin.

Data-driven study/optimization of a solar power and cooling generation system in a transient operation mode and proposing a novel multi-turbine modification concept to reduce the sun's intermittent effect

This study explores the integration of solar energy via parabolic trough collectors (PTC) with the Goswami cycle, focusing on evaluating life cycle costs (LCC) and energy performance in both steady-state and transient conditions. A suitable system configuration of a single-turbine Goswami cycle is designed for integration with PTC. Then, in the system's steady-state, a parametric study is performed based on the change in the design components. Subsequently, a multi-objective optimization method using energy and lifetime cost objectives are defined to identify the best system performance. This optimization technique utilizes artificial neural network (ANN) and the grey wolf optimizer (GWO) algorithm. Accordingly, the transient performance of the system is investigated during its optimal operating point using the TRNSYS software. Suitable controllers are considered for regulating power production and cooling system. Annual transient performance graphs of the systems are obtained. Following these investigations, a novel multi-turbine system is proposed. This configuration aims to enhance system reliability and diminish the reliance on storage devices by optimizing performance. The proper configuration of the five-turbine system with the required controllers is also provided. Hence, the method of dividing the turbine into similar turbines with lower capacity is a new concept proposed in this study. In the optimal state, it is observed that for 100 kW of net power output, 161 kW of effective cooling load can be achieved. At this configuration, the system's LCC amounts to 2.91 M. Moreover, during transient operation, an average power of 90 kW is attainable with a cooling load of 120 kW. The findings indicate that modifying the system from single turbine to five-turbines incurs an additional cost of approximately 9.2 % and reduces power output by 6 %. However, this modification significantly mitigates the transient impact of solar fluctuations.

Study of turbulence intermittency in unstable atmospheric surface layer and its effect on saltation sand motion based on wavelet transform

Turbulence in the atmospheric surface layer, especially in deserts and semi-arid regions, significantly affects sand movement. In unstable stratification, turbulence exhibits complex intermittency, complicating its impact on saltation. This study uses wavelet transform analysis to examine the effects of turbulence intermittency in unstable stratification on saltation. Our analysis reveals that in unstable stratification, the energy distribution of turbulence is more dispersed, the intermittent characteristics are more significant, and the intermittent burst duration of streamwise turbulence is longer, while the vertical intermittent burst duration is shorter. The fitting formulas of the energy ratio and stratification stability of the streamwise wind speed, vertical wind speed, and temperature at different frequencies are given. In addition, there is a complex nonlinear relationship between stratification stability and friction velocity on saltation. In unstable stratification, the critical wind speed required for saltation is higher than that of near-neutral, and the jumping speed and horizontal transport are weakened. Moreover, the coherence between wind speed and saltation flux increases significantly at low frequency with the increase in instability, indicating that large-scale motion plays a key role in saltation under these conditions. The more unstable the stratification is, the more obvious the phase difference fluctuation of the low frequency part is, and the more unfavorable the formation of stable saltation sand conditions. This study reveals the turbulence intermittently and its complex effects on sand particle movement in unstable stratification, which is of great significance for predicting and controlling dust storms, land desertification, and soil erosion.

Ghana and the IMF: Policy shifts, economic bailouts and macroeconomic outcomes

Ghana has a long history of engagement with the IMF. Successive governments of Ghana have sought economic bailouts from the IMF due to worsening domestic macroeconomic stability. This paper examines Ghana’s historical engagement with the IMF and the associated macroeconomic outcomes, and offers lessons for economic restructuring and growth beyond the bailouts. The paper explores the common patterns of the key macroeconomic variables and possible latent causal effects. The results reveal intermittent and short-term effects of the IMF programs. The bailouts often have a short-term impact on macroeconomic stability and growth, but the effects are unsustainable in the long term, especially after the IMF program ends.

Development of the energy hub GEDERlab at Universitat Politècnica de València for encouraging the integration of renewable energy resources

Renewable energies stand out as fundamental solutions to address climate change, providing environmental benefits and promoting energy independence. However, renewable plants face challenges such as intermittency, initial costs, and visual effects on the surroundings. The GEDERlab is an innovative energy hub developed at the Universitat Politècnica de València (UPV) that integrates four renewable energies (solar, wind, biogas, and hydraulic) to tackle these challenges. The main objective is only to optimize complementarity among energies but also to develop strategies for efficient storage and optimal management. This project goes beyond research and it aims to become a replicable model at the municipal level. Therefore, the results are extrapolated to a rural municipality in the Valencian Community, to improve energy efficiency, promote circular economy principles and utilize waste as resources. So, in this paper, the components of the energy hub GEDERlab, their integration, and the control system are described to encourage the integration of renewable energy resources.

Mesoclimate scale effects of river intermittency on aquatic insects in Seto Inland Sea watersheds, Western Japan

AbstractThe responses of assemblages and ecosystems to river intermittency are often considered on large spatial scales, such as those associated with the Köppen climate classification. However, river intermittency may naturally occur even in humid regions, and the effects may differ from those where intermittency occurs throughout the area. This study aimed to examine the differences in taxonomic and trait composition of aquatic insects between intermittent rivers in the Seto Inland Sea watersheds and neighboring humid-temperate rivers in Japan using national census data. While the climate in the most part of the Japanese Archipelago is categorized as humid-temperate, and rivers are usually perennial, local climate in the Seto Inland Sea watersheds has low summer precipitation compared with that in neighboring regions, thereby resulting in river intermittency. Consistent with the previous studies in the regions where rivers are intermittent on a large spatial scale, we observed that aquatic insects with multivoltinism and/or aerial respiration notably tolerated river intermittency. In contrast, the aquatic insect fauna in Japanese intermittent rivers represented subsets of those in the humid-temperate rivers, although previous studies such in Mediterranean regions have reported high endemism and species diversity in intermittent rivers. These results highlight the importance of exploring the role of river intermittency on small to medium spatial scales, as well as on large scales, to project effects of ongoing and future climate changes on species diversity.

Implementation of pumped hydro/photovoltaic systems in mining-degraded areas: a case study in Quadrilátero Ferrífero, Minas Gerais, Brazil

This work presents a proposal for the transformation of mining-degraded areas into renewable energy installations, converting deactivated mine pits, in the Quadrilátero Ferrífero (QF) region in state of Minas Gerais (MG), Brazil, into reservoirs for Pumped Storage Hydropower (PSH). Additionally, it proposes the alteration of adjacent areas impacted by mining extraction process, through their conversion into Photovoltaic Power Plants (PV). This measure has the potential to turn mining liabilities into sources of energy with lower environmental impact and sustainability for society. This process allows energy to be stored in the form of hydraulic batteries, which can mitigate the effects of intermittency of photovoltaic generation in the electrical grid. The presented methodology involves mapping deactivated mines, calculating the energy potential of the coupled PSH and PV systems, and conducting an economic feasibility study for PSH implementation. The work includes a case study discussing potential local environmental impacts and the energy potentials of this solution. The case study resulted in identifying a suitable pair of mine pits for a PSH in the QF, capable of supplying the electrical grid with approximately 234.3 MW, with the generated energy cost ranging between U$112.26/MWh to U$167.22/MWh. It is concluded that utilizing inactive mines as PSH reservoirs and installing PV in adjacent mining-degraded areas are innovative and technologically feasible strategies. Economically, their implementation will depend on the market price of energy.

A detective story of intermittent fasting effect on immunity.

Intermittent fasting (IF) refers to periodic fasting routines, that caloric intake is minimized not by meal portion size reduction but by intermittently eliminating ingestion of one or several consecutive meals. IF can instigate comprehensive and multifaceted alterations in energy metabolism, these metabolic channels may aboundingly function as primordial mechanisms that interface with the immune system, instigating intricate immune transformations. This review delivers a comprehensive understanding of IF, paying particular attention to its influence on the immune system, thus seeking to bridge these two research domains. We explore how IF effects lipid metabolism, hormonal levels, circadian rhythm, autophagy, oxidative stress, gut microbiota, and intestinal barrier integrity, and conjecture about the mechanisms orchestrating the intersect between these factors and the immune system. Moreover, the review includes research findings on the implications of IF on the immune system and patients burdened with autoimmune diseases.

Relationship between Hypoxia and Hypercapnia Tolerance and Life Expectancy.

The review discusses the potential relationship between hypoxia resistance and longevity, the influence of carbon dioxide on the mechanisms of aging of the mammalian organism, and intermittent hypercapnic-hypoxic effects on the signaling pathways of aging mechanisms. In the article, we focused on the potential mechanisms of the gero-protective efficacy of carbon dioxide when combined with hypoxia. The review summarizes the possible influence of intermittent hypoxia and hypercapnia on aging processes in the nervous system. We considered the perspective variants of the application of hypercapnic-hypoxic influences for achieving active longevity and the prospects for the possibilities of developing hypercapnic-hypoxic training methods.

Conductive hydro-drying of cayenne chili paste: Effects of intermittency, temperature and salt concentration on product quality and energy efficiency

Cayenne chili paste, which has a high moisture content, can be preserved by drying and adding salt. A Box-Behnken design was used to investigate the effects of added salt (0, 7.5 and 15 g salt/100 g paste), intermittent heating (cycles of 15 min on and 0, 15 or 30 min off), and water temperature (70, 80, 90 °C) on the physicochemical properties, capsaicinoid content, total phenolic content (TPC), antioxidant capacity (AC) and energy efficiency. Salt content significantly affected drying time and product moisture, density, color, TPC and AC. The intermittency increased the concentrations of TPC and AC and decreased energy consumption by up to 31%. Drying at 90 °C significantly reduced the processing time compared to drying at 70 °C, preserving the color and capsaicinoid content (18.3–59.0 mg/100 g dry matter). Dried cayenne chili paste produced by intermittent conductive hydro-drying had higher quality than product from a continuous process, drying times were similar and the process was more energy efficient.

The effect of intermittency in wave forcing on the quasi-biennial oscillation

The effect of intermittency in wave forcing on the quasi-biennial oscillation

Estimation of useful-stage energy returns on investment for fossil fuels and implications for renewable energy systems

The net energy implications of the energy transition have so far been analysed at best at the final energy stage. Here we argue that expanding the analysis to the useful stage is crucial. We estimate fossil fuelsʼ useful-stage energy returns on investment (EROIs) over the period 1971–2020, globally and nationally, and disaggregate EROIs by end use. We find that fossil fuelsʼ useful-stage EROIs (~3.5:1) are considerably lower than at the final stage (~8.5:1), due to low final-to-useful efficiencies. Further, we estimate the final-stage EROI for which electricity-yielding renewable energy would deliver the same net useful energy as fossil fuels (EROI equivalent) to be approximately 4.6:1. The EROIs of electricity-yielding renewable energy systems, based on published estimations, are found to be higher than the determined EROI equivalent, even considering the effects of intermittency under a range of energy transition scenarios. Results suggest that the energy transition may happen without a decline in net useful energy, countering the view that renewable energy systems cannot replace fossil fuels without incurring a substantial energy penalty.

Intermittent fasting alleviates IMQ-induced psoriasis-like dermatitis via reduced γδT17 and monocytes in mice.

Psoriasis is a chronic immune mediated inflammatory skin disease with systemic manifestations. It has been reported that caloric restriction could improve severity of psoriasis patients. However, the mechanism of intermittent fasting effects on psoriasis has not been investigated. Caloric restriction is known to reduce the number of circulating inflammatory monocytes in a CCL2-dependent manner. However, it is still unknown whether caloric restriction can improve psoriasis by regulating monocytes through CCL2. In this study, we used imiquimod (IMQ)-induced psoriasis-like mouse model to explore the effects and the mechanisms of intermittent fasting on psoriasis-like dermatitis. We found that intermittent fasting could significantly improve IMQ-induced psoriasis-like dermatitis, and reduce the number of γδT17 cells and IL-17 production in draining lymph nodes and psoriatic lesion via inhibiting proliferation and increasing death of γδT17 cells. Furthermore, intermittent fasting could significantly decrease monocytes in blood, and this was associated with decreased monocytes, macrophages and DC in psoriasis-like skin inflammation. Reduced monocytes in circulation and increased monocytes in BM of fasting IMQ-induced psoriasis-like mice is through reducing the production of CCL2 from BM to inhibit monocyte egress to the periphery. Our above data shads light on the mechanisms of intermittent fasting on psoriasis.

Stochastic models in the under-resolved simulations of spray formation during high-speed liquid injection

In the under-resolved simulation of the high-speed liquid injection into stagnant air, the attention in subgrid-scale models is focused on events of intense gradients of the velocity in turbulent flow, i.e., on effects of intermittency. Three typical flows are considered—the in-nozzle flow, primary atomization zone, and secondary atomization of spray droplets. In the simulation of the first two flows, the filtered Navier–Stokes equations are forced by stochastic processes with properties which incorporate the statistical physics of fluid acceleration at the high Reynolds number—in this way we update the under-resolved acceleration. In the case of in-nozzle flow, the proposed stochastic subgrid acceleration model is combined with wall-damping function, and the ability in prediction of the velocity statistics is demonstrated. In the simulation of primary atomization, the approach with stochastic subgrid acceleration is combined with the volume of fluid method. This leads to intensification of the interface dynamics, resulting in additional corrugation, with more intense shearing and stretching of liquid structures are observed. Thereby, the experimental profiles of the time-averaged liquid volume fraction distribution for four different axial locations are rather well predicted. The secondary atomization of droplets is simulated by a new stochastic model for the breakup rate along the droplet path. To this end, the breakup rate is expressed as a function of turbulent viscous dissipation which evolves along the droplet path according to the proposed stochastic process. Preliminary assessment performed against the recent experiments shows the correct predictability of this model and its low sensibility to the grid density.

Turbulence Intermittency Effects on the Initiation Threshold of Sediment Motion in Natural Waters

AbstractThe initiation threshold of sediment motion, a key component in quantifying sediment transport, has potential link to intermittent turbulence bursts. Here, we elaborated in situ experiments on coastal sea bottom covered with cohesive sediments, to obtain intermittency parameters. The variable “waiting time” between turbulence bursts was utilized to capture the occurrence of sediment initiation events in natural waters. A relationship between waiting time and shear stress reveals the different intermittency features of sediment flux time series before and after reaching the threshold, which can be used to determine the initiation threshold of sediment motion. Multi‐site results demonstrate the limitations of traditional empirical formulae for fine‐grained sediments, where cohesiveness becomes more pronounced as grain size decreases and the deviation can reach 600%. The empirical formula was modified using grain size, and the modified calculations were in good agreement with observed values, which will greatly assist in sediment transport and geomorphology model predictions.

Dual effects of drying and urban pollution on leaf litter decomposition and shredder consumption in permanent and intermittent streams

In the present study we investigated the combined effect of flow intermittence and wastewater treatment plant (WWTP) effluent on leaf litter decomposition in two Mediterranean streams with permanent and intermittent flow regimes. The litter decomposition experiment was performed using black poplar litter bags where we measured litter mass loss, fungal biomass, aquatic hyphomycete sporulation and species richness and C:N ratio. Afterwards, the remaining litter material from the different treatments was offered to the shredder Potamophylax latipennis in a microcosm laboratory experiment, and its growth and consumption rates were studied. We hypothesised that drying would decrease leaf litter decomposition in the permanent stream more than in the intermittent stream and that WWTP effluent would compensate for drying effects when both stressors interacted. The results indicated that drying has the greatest impact on the permanent stream, decreasing decomposition, aquatic hyphomycete species richness, and leaf litter quality. In the intermittent stream, WWTP effluent decreases aquatic hyphomycete species richness, but drying increases it, showing an opposing effect and a synergistic interaction. In the permanent stream drying provoked an increase in the shredder consumption rate. Thus, the expected more frequent intermittence in rivers under climate change may threaten the processing of organic matter.

Falling, deformation, and coalescence of droplet in model waxy oil under an electric field

Electrocoalescence technology can efficiently dehydrate waxy crude oil but the mechanisms are still unclear. Herein, the continuous microscopic behaviors of droplet falling, deformation, and coalescence were experimentally investigated to clarify the dynamic response mechanism of droplet in waxy oil under an electric field. The results showed the droplet falling under both gravity and electrostatic attraction to deform by the electric field force. Moreover, the expansion and clamping of the liquid bridge resulted from the competition between electric field force and capillary force. However, the precipitated wax crystals reduced the kinetic energy of the droplet and affected its external circulation, thus delaying the falling time. In addition, the wax crystals with interfacial activity adsorbed on the oil-water interface and cross-linked to form a spatial network structure, thereby weakening droplet deformation, hindering liquid film drainage, and inhibiting liquid bridge expansion. Importantly, the droplet adsorbed wax crystals exhibited interfacial elasticity, which makes them more inclined to partial coalescence. The low-frequency pulsed direct current (PUDC) electric field with high strength intermittent effect displayed the most obvious inhibition effect on the wax crystals. Overall, these findings look promising for future design and optimization of high-efficiency electric dehydrators and related fields.