Flux Fluctuations Research Articles

Abstract Extreme scattering events (ESEs) are observed as large fluctuations in radio flux from point-like sources. ESEs may originate in interstellar structures with linear dimensions of ∼1 au, electron densities of 10–100 cm −3 , and transverse speeds of order 100 km s −1 . These parameters overlap with corresponding parameters associated with solar coronal mass ejections (CMEs). I suggest that stellar CMEs from flare stars may contribute significantly to the ESE phenomenon.

Lithium (Li) metal anodes, despite their exceptional theoretical capacity (3860mAhg-1), suffer from severe dendrite growth, electrolyte decomposition, and structural instability caused by uneven Li-ion flux and significant volume fluctuations. Here, a one-step, scalable fabrication of 3D hosts that synergistically couple tortuosity modulation with a spatially graded lithiophilicity via precise control of demixing kinetics in a nonsolvent-induced phase separation process is reported. Low-tortuosity (LT) hosts integrate vertically aligned channels for fast ion transport with a silver-gradient interface that directs bottom-up Li deposition, enabling concurrent suppression of dendrites and accommodation of plating-induced volume expansion (4.4% swelling). Finite element simulations confirm the cooperative role of structural alignment in mitigating ion depletion and of chemical gradients in guiding uniform deposition, jointly ensuring stable Li cycling. The LT host sustains >5500h at 1C in symmetric cells and delivers superior durability in full cells with limited-Li anodes (4mAhcm-2) paired with LiFePO4 and high-loading LiNi0.8Co0.1Mn0.1O2 cathodes. Double-stacked pouch cells (N/P=0.8, E/C=2.5gAh-1) achieve 398.1Whkg-1 and 1516.8WhL-1, retaining 94.2% capacity after 80 cycles. This structural-chemical integration strategy offers a practical, scalable route toward next-generation high-energy-density Li metal batteries.

We explore the intriguing phenomenon of time non-locality in the evolution of dark matter and Large Scale Structure (LSS). Recently in [1], it was shown that time non-locality emerges in bias tracer fluctuations, which are SO(3) scalars in real space, at fifth order in the perturbation expansion in dark matter overdensity. We demonstrate that by breaking the symmetry down to SO(2), which is the case whenever line-of-sight effects become important, such as for flux fluctuations in the Lyman α forest, the temporal non-locality appears at the third order in expansion. Additionally, within the framework of EFTofLSS, we demonstrate that time non-locality manifests in the effective stress tensor of dark matter, which is a second rank tensor under SO(3) transformations, again at the third order in dark matter overdensity. Furthermore, we highlight the effectiveness of the standard Π basis [2] in handling time non-local operators.

In this study, the effect of the slab continuous casting mold thickness on the mold flow field, the fluctuation of the mold flux and molten steel interface (MF‐MSI), the solidification of molten steel, and the removal and capture of bubbles and inclusions is investigated by numerical simulation and high‐temperature quantitative measurement of the mold surface flow velocity (MSFV). With an increase in the thickness from 180 to 250 mm and 320 mm, the measurement results decrease from 0.2148 m s−1 to 0.2074 m s−1 and 0.1875 m s−1, respectively. The numerical simulation results present excellent alignment with high‐temperature measurement results of MSFV. The occurrence ratios of the mold flux, bubble, and inclusion defects are all reduced. The values of ΔH decrease from 12.91 mm to 11.79 mm and 9.43 mm. The ratios of the bubbles captured by the solidified shell decrease from 1.25% to 0.86% and 0.58%, the ratios of inclusions removed by the mold flux layer increase from 29.01% to 29.80% and 33.90%, and the ratios of inclusions captured by the solidified shell decrease from 33.69% to 28.76% and 23.54%, respectively.

The regional features of seasonal variability of ion flux in the Kuban River basin for the period 1990-2020 in the context of climatic changes and anthropogenic impact are considered. The study was based on long-term hydrochemical and hydrological data of the state observation network of Roshydromet. Statistically significant ion flux trends were determined using the Kendall rank correlation coefficient. The method of normalized difference-integral curves was used to identify contrasting periods of ion flux. Differences between the selected periods were assessed using the non-parametric Mann-Whitney test. It is shown that the intra-annual variability of ion flux in the Kuban River basin is determined by the water runoff of rivers. The analysis of the long-term dynamics of ion flux made it possible to identify contrasting periods of flux of substances. In the sites Protoka - Slavyansk-on-Kuban, Protoka - Slobodka, Pshish - Khadyzhensk, Psekups - Goryachiy Klyuch, there was a statistically significant decrease in ionic flux. The seasonal values of ion flux calculated for the selected periods made it possible to trace its changes during the change of contrasting periods of long-term dynamics. It is shown that the direction of seasonal fluctuations in ion flux corresponded to long-term variability - there was a decrease in the flux of substances in all seasons of the year.

Abstract Recent studies suggest that numerous intermediate-mass black holes (IMBHs) may wander undetected across the Universe, emitting little radiation. These IMBHs largely preserve their birth masses, offering critical insights into the formation of heavy black hole seeds and the dynamical processes driving their evolution. We propose that such IMBHs could produce detectable microlensing effects on quasars. Their Einstein radii, comparable to the scale of quasar broad-line regions, magnify radiation from the accretion disk and broad emission lines, making these quasars outliers in flux scaling relations. Meanwhile, the microlensing causes long-term, quasi-linear variability that is distinguishable from the stochastic variability of quasars through its coherent multiwavelength behavior. We develop a matched-filtering technique that effectively separates the long-term lensing signal from the intrinsic quasar variability, with sensitivity tripling each time the observational time span doubles. Moreover, as IMBHs are often surrounded by dense star clusters, their combined gravitational field produces substantial extended, concentric caustics. These caustics induce significant variability in optical, ultraviolet, and X-ray bands over decade timescales, alongside hour-to-day-scale flux fluctuations in broad emission lines. We predict a substantial number of detectable events in the upcoming surveys by the Vera C. Rubin Observatory, considering recent IMBH mass density estimates. Even in the absence of positive detections, searches for these microlensing signals will place meaningful constraints on the cosmological mass density of IMBHs, advancing our understanding of their role in cosmic evolution.

Alongside technological advancement, there is a growing need for materials that are easier to obtain and process and that offer multiple uses, thereby reducing environmental impact. Such materials are generally subject to mechanical, resistance and fatigue studies, often without considering their thermal properties, which could potentially expand the range of applications for the studied compound. The current study aims to analyze possible fluctuations and deviations from linearity in temperature flow curves, as well as their impact on the conductivity coefficient. These studies are conducted on a new type of panel made of fiberglass, a low-cost material with significant recycling potential, using foam elements recycled from packaging insulations and a cement biding mixture. This study considers the time variation of the different thermal coefficients and the temperature curves obtained from the experimental measurements. These data are analyzed and used to simulate heat variation in order to observe the heat flux fluctuations within the plate. The results suggest that the proposed composite plate can serve as an alternative to classical insulating panels.

In the present study, we investigate the modulation effects of particles on compressible turbulent boundary layers at a Mach number of 6, employing high-fidelity direct numerical simulations based on the Eulerian–Lagrangian point-particle approach. Our findings reveal that the mean and fluctuating velocities in particle-laden flows exhibit similarities to incompressible flows under compressibility transformations and semi-local viscous scaling. With increasing particle mass loading, the reduction in Reynolds shear stress and the increase in particle feedback force constitute competing effects, leading to a non-monotonic variation in skin friction, particularly in turbulence over cold walls. Furthermore, dilatational motions near the wall, manifested as travelling-wave structures, persist under the influence of particles. However, these structures are significantly weakened due to the suppression of solenoidal bursting events and the negative work exerted by the particle feedback force. These findings align with the insight of Yu et al. (J. Fluid. Mech., vol. 984, 2024, A44), who demonstrated that dilatational motions are generated by the vortices associated with intense bursting events, rather than acting as evolving perturbations beneath velocity streaks. The attenuation of travelling-wave structures at higher particle mass loadings also contributes to the reduction in the intensities of wall shear stress and heat flux fluctuations, as well as the probability of extreme events. These results highlight the potential of particle-laden flows to mitigate aerodynamic forces and thermal loads in high-speed vehicles.

Abstract Latent energy storages associated with renewable energy devices and electronics cooling systems generally experience irregular heat transfer supplies leading to large temperature or heat flux variations in the heat transfer boundary. Wavy heat transfer surfaces are widely recognized as a heat transfer enhancement alternative in heat transfer fluid systems owing to their superior thermal performance. A detailed elucidation of melting dynamics and thermal performance of a latent energy storage with a wavy heat transfer boundary subjected to boundary heat fluctuations having a time scale comparable to that of a melt convection system is presented here. A finite volume-based computational model with enthalpy-porosity technique incorporating transient temperature boundary conditions has been developed and successfully validated with experimental visualization and temperature measurements in phase change material (PCM) storage with a wavy heat-transferring surface. Extensive numerical simulations are performed to figure out the makeovers in laminar thermal convection in molten PCM adjacent to a wavy heat transfer boundary for various levels of temperature fluctuations. Clear elucidations of melt front developments, melt convection, and resulting heat transfer estimates for different levels of boundary temperature fluctuations are presented. Correlations among key dimensionless parameters have been developed based on the detailed thermal performance estimations carried out in this study.

The probability distribution for vacuum fluctuations of the energy flux in two dimensions is constructed, along with the joint distribution of energy flux and energy density. Our approach is based on previous work on probability distributions for the energy density in two-dimensional conformal field theory. In both cases, the relevant stress tensor component must be averaged in time, and the results are sensitive to the form of the averaging function. Here we present results for two classes of such functions, which include the Gaussian and Lorentzian functions. The distribution for the energy flux is symmetric, unlike that for the energy density. In both cases, the distribution may possess an integrable singularity. The functional form of the flux distribution function involves a modified Bessel function and is distinct from the shifted Gamma form for the energy density. By considering the joint distribution of energy flux and energy density, we show that the distribution of energy flux tends to be more centrally concentrated than that of the energy density. We also determine the distribution of energy fluxes, conditioned on the energy density being negative. Some applications of the results are also discussed. Published by the American Physical Society 2025

We investigate convection in a thin cylindrical gas layer with an imposed flux at the bottom and a fixed temperature along the side, using a combination of direct numerical simulations and laboratory experiments. The experimental approach allows us to extend by two orders of magnitude the explored range in terms of flux Rayleigh number. We identify a scaling law governing the root-mean-square horizontal velocity and explain it through a dimensional analysis based on heat transport in the turbulent regime. Using particle image velocimetry, we experimentally confirm, for the most turbulent regimes, the presence of a drifting persistent pattern consisting of radial branches, as identified by Rein et al. (2023, J. Fluid Mech.977, A26). We characterise the angular drift frequency and azimuthal wavenumber of this pattern as functions of the Rayleigh number. The system exhibits a wide distribution of heat flux across various time scales, with the longest fluctuations attributed to the branch pattern and the shortest to turbulent fluctuations. Consequently, the branch pattern must be considered to better forecast important wall heat flux fluctuations, a result of great relevance in the context of nuclear safety, the initial motivation for our study.

The high primary productivity zone (HPPZ) of estuaries is known for its flourishing fisheries and active interactions with coastal and oceanic ecosystems. However, the spatiotemporal patterns and underlying mechanisms that regulate the HPPZ remain unclear, especially in the face of drastic changes in riverine inputs. Using 40 years of in situ monitoring data along the Yangtze River estuary, the spatiotemporal evolution of the HPPZ regulated by basin-estuarine-offshore flux fluctuations has been reconstructed for the past and conclusions drawn for future developments. Moreover, the biological processes that influence the formation of the HPPZ were explored within the context of estuarine filtration and buffering effects. The obtained dataset includes chlorophyll a (Chl-a) concentrations and multiple environmental factors. The results displayed that the HPPZ is characterized by a high annual average Chl-a concentration of 3.6 ± 2.4 μg/L, which is driven by sufficient light and nutrient availability that promote phytoplankton blooms. In contrast, the inner high turbidity zone exhibits an average annual Chl-a concentration of 1.0 ± 0.7 μg/L, primarily due to limited light availability inhibiting phytoplankton growth. Meanwhile, the outer lower nutrient zone, with an average annual Chl-a concentration of 0.9 ± 1.1 μg/L, results from nutrient deficiencies that limit phytoplankton growth. Notably, the synergistic effect of sediment declines and eutrophication has resulted in a 6.5 μg/L increment of the HPPZ’s annual Chl-a concentration and a 3628 km² expansion of its area extent over 40 years. This significant change is attributed to the increase in water transparency resulting from a reduction in sediment transported from the watershed to the sea, along with an increase in riverine nitrogen and phosphorus discharge. A future projection, based on the historical total suspended matter and nutrients over the past 40 years, suggests that annual Chl-a concentration in the HPPZ will reach 10.5 μg/L, and the area is projected to increase to 7,904 km² by 2050. This study presents the first quantification of Chl-a concentrations and spatial range of the HPPZ in the estuary, focusing on the interaction between riverine and oceanic materials. These findings offer a deeper understanding of managing ecological risks in large estuaries.

We present an effective field theory (EFT) approach to extract fundamental cosmological parameters from the Lyman-alpha forest flux fluctuations as an alternative to the standard simulation-based techniques. As a first application, we reanalyze the publicly available one-dimensional Lyman-alpha flux power spectrum data from the Sloan Digital Sky Survey. Our analysis relies on informative priors on EFT parameters that we extract from a combination of public hydrodynamic simulation and emulator data. Assuming the concordance cosmological model, our one-parameter analysis yields a 2% measurement of the late time mass fluctuation amplitude σ_{8}=0.841±0.017, or equivalently, the structure growth parameter S_{8}=0.852±0.017, consistent with the standard cosmology. This result is obtained assuming that nonlinear EFT parameters are cosmology-independent functions of the linear bias parameter. When this assumption is loosened, the limit degrades by a factor of 3, suggesting that informative priors are necessary for competitive constraints. Combining our EFT likelihood with Planck+baryon acoustic oscillation data, we find a new constraint on the total neutrino mass, ∑m_{ν}<0.08 eV (at 95%CL). Our study defines priorities for the development of EFT methods and sets the benchmark for cosmological analyses of the Lyman-alpha forest data from the Dark Energy Spectroscopic Instrument.

Algorithms that constrain metabolic network models with enzyme levels to predict metabolic activity assume that changes in enzyme levels are indicative of flux variations. However, metabolic flux can also be regulated by other mechanisms such as allostery and mass action. To systematically explore the relationship between fluctuations in enzyme expression and flux, we combine available yeast proteomic and fluxomic data to reveal that flux changes can be best predicted from changes in enzyme levels of pathways, rather than the whole network or only cognate reactions. We implement this principle in an ‘enhanced flux potential analysis’ (eFPA) algorithm that integrates enzyme expression data with metabolic network architecture to predict relative flux levels of reactions including those regulated by other mechanisms. Applied to human data, eFPA consistently predicts tissue metabolic function using either proteomic or transcriptomic data. Additionally, eFPA efficiently handles data sparsity and noisiness, generating robust flux predictions with single-cell gene expression data. Our approach outperforms alternatives by striking an optimal balance, evaluating enzyme expression at pathway level, rather than either single-reaction or whole-network levels.

The smooth-wall transition process was characterized during flight at Mach 6.0 on a research geometry with concave curvature and swept leading edges, which introduced a boundary layer with stationary laminar vortex streaks, competing transition mechanisms, and complex early turbulence. This flight, termed BOLT II, was the second in a series coordinated by the Air Force Office of Scientific Research. Surface heat flux, skin friction, and pressure fluctuation spectra were acquired to characterize the transition process. Transition was first observed in a mixed second mode and crossflow mode region on −Z side of the vehicle at Rex=4.0−6.0×106. The mixed-mode transition appeared to occur in a narrow streak between 0.10 and 0.12 m off the centerline. In the +Z-side mixed-mode region, transition took place at higher Reynolds numbers, Rex=7.0−10.0×106. The analyses also showed that the spatial evolution to turbulence varied with respect to the location of the vortex heating streaks. Near the centerline, the flow experienced transition at Rex=5.5−7.5×106. This transition front bifurcated as it moved upstream, which indicated correlation to near-centerline counter-rotating roll-up vortices. High-frequency pressure data captured major transition modes on the −Z half of the vehicle, including the near-centerline vortex (100–200 kHz), mixed mode (300–500 kHz), and a higher-frequency mode (650–750 kHz) further outboard.

Composite phase-change materials (PCMs) exhibit significant potential for enhancing the thermal performance of building walls. However, previous studies have generally lacked detailed investigations of the performance of PCM-integrated walls under cold climate conditions. Therefore, in order to evaluate the thermal performance and wall adaptability of hollow bricks with composite PCMs in cold climates, a brick model was created by filling the hollow bricks with PCMs. Then a comparative test was conducted between the PCM-filled bricks and the conventional non-PCM-filled hollow bricks. The comparative experimental method and the thermal performance index evaluation method resulted in the following: (1) Compared with conventional hollow bricks, PCM-filled bricks showed an increase of approximately 0.99 °C in inner surface temperature and 3.85 °C in midsection temperature. This demonstrates that PCM-filled bricks can retard the rate of temperature drop, significantly enhancing the insulation performance of walls. This improvement contributes to enhance indoor thermal comfort and reduce energy consumption. (2) The temperature difference between the interior and exterior surfaces of the non-PCM-filled hollow bricks is 23.54 °C, which is 5.62 °C higher than that of the PCM-filled bricks. This indicates that bricks filled with PCMs possess superior heat storage capacity, effectively reducing indoor heat loss, which aligns with the principles of green building design. (3) Compared with the conventional non-PCM-filled hollow bricks, the heat flow on the inner surface of the PCM-filled bricks is significantly lower, with the average heat flow reduced by 8.57 W/m2. This suggests the ability of bricks filled with PCMs to moderate heat flux fluctuations through a “peak-shaving and valley-filling” effect, contributing to reduced energy consumption and enhanced occupant thermal comfort.

The physics of planetary climate features a variety of complex systems that are challenging to model as they feature turbulent flows. A key example is the heat flux from the upper ocean to the underside of sea ice which provides a key contribution to the evolution of the Arctic sea ice cover. Here, we develop a model of the turbulent ice-ocean heat flux using coupled ordinary stochastic differential equationsto model fluctuations in the vertical velocity and temperature in the Arctic mixed layer. All the parameters in the model are determined from observational data. A detailed comparison between the model results and measurements made during the Surface Heat Budget of the Arctic Ocean (SHEBA) project reveals that the model is able to capture the probability density functions (PDFs) of velocity, temperature, and heat flux fluctuations. Furthermore, we show that the temperature in the upper layer of the Arctic Ocean can be treated as a passive scalar during the whole year of SHEBA measurements. The stochastic model developed here provides a computationally inexpensive way to compute an observationally consistent PDF of this heat flux and has implications for its parametrization in regional and global climate models.

ABSTRACT Ignition experiments were performed with individual n-decane droplets, initially, about 1 mm in diameter, which were suspended in quartz fibers and subjected to electrical discharges (sparks) of controlled power and duration. Experiments were performed with glow and arc discharges in air at 1 atm and approximately 300 K . Theory is developed to predict the probability of ignition of a fuel droplet as a function of time when it is exposed to an ignition spark. The theory considers the effect of random spark-to-spark fluctuations in the heat flux into the liquid on the time for the droplet surface temperature to be high enough to enable ignition. A Bayesian analysis is also performed to evaluate confidence intervals for parameters related to droplet ignition. Reasonable agreement between theory and experiment is demonstrated, suggesting that spark-to-spark fluctuations of the heat flux into a droplet may lead to a sigmoidal variation of the probability of ignition with respect to time.

Abstract Carbon dioxide () fluxes in regulated Alpine rivers are driven by multiple biogeochemical and anthropogenic processes, acting on different spatiotemporal scales. We quantified the relative importance of these drivers and their effects on the dynamics of concentration and atmospheric exchange fluxes in a representative Alpine river segment regulated by a cascading hydropower system with diversion, which includes two residual flow reaches and a reach subject to hydropeaking. We combined instantaneous and time‐resolved water chemistry and hydraulic measurements at different times of the year, and quantified the main fluxes by calibrating a one‐dimensional transport‐reaction model with measured data. As a novelty compared to previous inverse modeling applications, the model also included carbonate buffering, which contributed significantly to the budget of the case study. The spatiotemporal distribution and drivers of fluxes depended on hydropower operations. Along the residual flow reaches, fluxes were directly affected by the upstream dams only in the first 2.5 km, where the supply of supersaturated water from the reservoirs was predominant. Downstream of the hydropower diversion outlets, the fluxes were dominated by systematic sub‐daily fluctuations in transport and evasion fluxes (“carbopeaking”) driven by hydropeaking. Hydropower operational patterns and regulation approaches in Alpine rivers affect fluxes and their response to biogeochemical drivers significantly across different temporal scales. Our findings highlight the importance of considering all scales of variations for accurate quantification and understanding of these impacts, to clarify the role of natural and anthropogenic drivers in global carbon cycling.

Thanks to advances in plasma science and enabling technology, mirror machines are being reconsidered for fusion power plants and as possible fusion volumetric neutron sources. However, cross-field transport and turbulence in mirrors remains relatively understudied compared with toroidal devices. Turbulence and transport in mirror configurations were studied utilizing the flexible magnetic geometry of the Large Plasma Device (LAPD). Multiple mirror ratios from $M=1$ to $M=2.68$ and three mirror-cell lengths from $L=3.51$ to $L=10.86$ m were examined. Langmuir and magnetic probes were used to measure profiles of density, temperature, potential and magnetic field. The electric field-fluctuation-driven ${\tilde {\boldsymbol{E}}} \times {\boldsymbol{B}}$ particle flux, where $\boldsymbol{B}$ is the background field, was calculated from these quantities. Two probe correlation techniques were used to infer wavenumbers and two-dimensional structure. Cross-field particle flux and density fluctuation power decreased with increased mirror ratio. Core density and temperatures remain similar with mirror ratio, but radial line-integrated density increased. The physical expansion of the plasma in the mirror cell by using a higher field in the source region may have led to reduced density fluctuation power through the increased gradient scale length. This increased scale length reduced the growth rate and saturation level of rotational interchange and drift-like instabilities. Despite the introduction of magnetic curvature, no evidence of mirror-driven instabilities – interchange, velocity space or otherwise – were observed. For curvature-induced interchange, many possible stabilization mechanisms were present, suppressing the visibility of the instability.