Density Dependence Research Articles

Anisotropic screening of excitons in van der Waals materials

Van der Waals (vdW) materials exhibit optical anisotropy due to the fundamental difference between in-plane (IP) covalent bonds and out-of-plane (OP) vdW bonds. In particular, InSe, a vdW material, provides an excellent platform for studying the optical properties of anisotropic excitons. We measure the energy difference between excitons with IP and OP dipole responses in InSe to be 0.4 meV. Under photoexcitation with femtosecond pulses, the photocarriers screen the excitons and can increase the energy difference between IP and OP optical responses to as much as 8 meV. This energy difference results from the varying screening lengths along the IP and OP directions. The change in energy difference persists for over 100 ps at 77 K, but recovers much faster, within 100 ps, at room temperature. The dependence of carrier density on the anisotropic screening of excitons has also been investigated.

Reduction of J c Anisotropy in REBCO Coated Conductors via Bilayer Structure of Columnar and Random Pinning Centers

Abstract To suppress the anisotropy of the angular dependence of the critical current density J c(θ) under high-temperature (T ∼ 77 K) and low-magnetic-field (B ≲ 3 T) conditions, where superconducting motor and generator applications are anticipated, we fabricated a bilayer structure comprised of a YBa2Cu3O7−δ (YBCO) thin film containing Y2O3 nano-particles (“Y-NP” layer) atop a EuBa2Cu3O7−δ (EuBCO) thin film containing BaHfO3 nano-rods (“Eu-NR” layer) deposited on a buffered metallic substrate. By comparing vortex pinning properties of the Eu-NR/Y-NP bilayer sample with those of single-layer Eu-NR and Y-NP samples, we found that introduced BaHfO3 nano-rods (BHO NRs) in the Eu-NR layer primarily enhance J c(θ) near the B∥c direction, whereas the Y2O3 nano-particles (YO NPs) improve J c(θ) near the B∥ab direction, where the effect of BHO NRs is less prominent. This complementary effect of BHO NRs (θ ∼ 0deg.) and YO NPs (θ ∼ 90deg.) successfully reduced the J c(θ) anisotropy at B [T] ≲ 8 − 0.375(T [K] − 65). Simulations of the J c(θ) anisotropy factor based on the measured J c(θ) data suggest that optimizing the volume fraction of Y-NP and Eu-NR layers could further minimize the J c(θ) anisotropy depending on (T, B) conditions.

Power production and area usage of offshore wind and the relationship with available energy in the atmosphere.

This paper presents an analysis of the area dependency of power and capacity density of wind farms, based on derivations of the available energy in the atmosphere and data on the power production of existing wind farms in the North Sea. The amount of available energy is determined by the mechanical energy budget of the atmospheric boundary layer and is found to be a function of C/A, where C is the circumference and A is the area of the wind farm. The actual power production of 31 wind farms is analyzed, and the power production in 23 of the largest wind farms follows the same functional form as the available energy, indicating that the power production in these wind farms is limited by the available energy. The power density in the North Sea, as a function of the area usage, is found by fitting the actual power density of existing wind farms to the expression for available energy in the atmospheric boundary layer. Wind farms below 10 km2 can produce more than 6 Wm-2, but the power density rapidly decreases with area. Wind farms with an area of about 1000 km2 will produce [Formula: see text] 1 Wm-2, and power densities will asymptotically approach a value of 0.78 [Formula: see text] 0.58 Wm-2 for increasing wind farm area. Since atmospheric energy input is the limiting factor for power production, an atmospheric energy budget is vital for a reliable estimate of offshore wind power potential.

Neural network distillation of orbital dependent density functional theory

Density functional theory (DFT) offers a desirable balance between quantitative accuracy and computational efficiency in practical many-electron calculations. Its central component, the exchange-correlation energy functional, has been approximated with increasing levels of complexity ranging from strictly local approximations to nonlocal and orbital dependent expressions with many tuned parameters. In this paper, we formulate a general way of rewriting complex density functionals using deep neural networks in a way that allows for simplified computation of Kohn-Sham potentials as well as higher functional derivatives through automatic differentiation, enabling access to highly nonlinear response functions and forces. These goals are achieved by using a recently developed class of robust neural network models capable of modeling functionals, as opposed to functions, with explicitly enforced spatial symmetries. Functionals treated in this way are then called and can be seamlessly integrated with existing DFT workflows. Tests are performed for a dataset featuring a large variety of molecular structures and popular meta–generalized gradient approximation density functionals, where we successfully eliminate orbital dependencies coming from the kinetic energy density, and discover a high degree of transferability to a variety of physical systems. The presented framework is general and could be extended to more complex orbital and energy dependent functionals as well as refined with specialized datasets. Published by the American Physical Society 2025

Impact of T- and ρ-dependent decay rates and new (n,γ) cross-sections on the s process in low-mass asymptotic giant branch stars

Aims. We study the impact of nuclear input related to weak-decay rates and neutron-capture reactions on predictions for the slow neutron-capture process (s process) in asymptotic giant branch (AGB) stars. We provide the first database of surface abundances and stellar yields of the isotopes heavier than iron from the Monash models. Methods. We ran nucleosynthesis calculations with the Monash post-processing code for seven stellar structure evolution models of low-mass AGB stars with three different sets of nuclear inputs. The reference set has constant decay rates and represents the set used in the previous Monash publications. The second set contains the temperature and density dependence of β decays and electron captures based on the default rates of nuclear NETwork GENerator (NETGEN). In the third set, we further update 92 neutron-capture rates based on re-evaluated experimental cross sections from the ASTrophysical Rate and rAw data Library. We compare and discuss the predictions of the sets relative to each other in terms of isotopic surface abundances and total stellar yields. We also compare the results to isotopic ratios measured in presolar stardust silicon carbide (SiC) grains from AGB stars. Results. The new sets of models result in a ∼66% solar s-process contribution to the p-nucleus 152Gd, confirming that this isotope is predominantly made by the s process. The nuclear input updates result in predictions for the 80Kr/82Kr ratio in the He intershell and surface 64Ni/58Ni, 94Mo/96Mo, and 137Ba/136Ba ratios that are more consistent with the corresponding ratios measured in stardust; however, the new predicted 138Ba/136Ba ratios are higher than the typical values of the SiC grains. The W isotopic anomalies are in agreement with data from the analyses of other meteoritic inclusions. We confirm that the production of 176Lu and 205Pb is affected by too large uncertainties in their decay rates from NETGEN.

Electrochemically Promoted Activation of Light Alkanes at Ambient Conditions

AbstractThe electrochemical activation of light alkanes into value‐added products represents a promising pathway for sustainable chemical synthesis and the storage of renewable energy. In this study, we introduce an electrochemically promoted system that employs copper plates as electrode and oxygen as oxidant, capable of converting ethane into ethylene and acetic acid with production rates of 6.9 and 6.2 µmol·cm−2Cu·h−1, respectively, with a combined selectivity exceeding 92%, under ambient conditions. Additionally, this system can convert propane to propylene at a rate of 11.6 µmol·cm−2Cu·h−1, with selectivity reaching up to 86%. A 10 h run with ethane demonstrates consistent production of ethylene and acetic acid, with a sustained selectivity above 96%, and achieves an acetic acid concentration of 19 mM. In situ spectroscopic analysis reveals the active surface and a critical reaction intermediate. Combining with partial pressure dependence study and density functional theory (DFT) calculations, we propose a potential reaction mechanism involving the competitive adsorption of oxygen and alkane producing an alkyl group as a key reaction step in the reaction process.

ExoALMA. XIV. Gas Surface Densities in the RX J1604.3−2130 A Disk from Pressure-broadened CO Line Wings

Abstract Gas surface density is one of the most relevant physical quantities in protoplanetary disks. However, its precise measurement remains highly challenging due to the lack of a direct tracer. In this study, we report the spatially resolved detection of pressure-broadened line wings in the CO J = 3–2 line in the RX J1604.3−2130 A transition disk as part of the exoALMA large program. Since pressure-broadened line wings are sensitive to the total gas volume density, we robustly constrain the radial dependence of the gas surface density and midplane pressure in the region located 50–110 au from the central star, which encompasses the dust ring of the system. The peak radius of the midplane pressure profile matches the dust ring radial location, directly proving radial dust trapping at a gas pressure maximum. The peak gas surface density is 18–44 g cm−2 and decreases at radii interior to and exterior of the dust ring. A comparison of the gas and dust surface densities suggests that the disk turbulence is as low as α turb ∼ 2 × 10−4. Despite dust trapping, the gas-to-dust surface density ratio at the ring peak is 70–400, which implies already-formed protoplanets and/or less efficient dust trapping. The gas surface density drop at radii interior to the ring is consistent with a gas gap induced by a Jupiter-mass planet. The total gas mass within 50 < r < 110 au is estimated to be ∼0.05–0.1 M ⊙(50–100 M Jup), suggesting that planetary system formation is possible.

Effects of temperature dependent density of the fluid on a plume generated by heat source in the presence of aligned magnetic field

ABSTRACT The current research focuses on the influences of the fluid’s temperature density on a plume generated by a heat source under the influence of an aligned magnetic field. For this purpose, the conservative equations of the flow model are modified in terms of temperature-dependent density. In order to investigate the problem, a mathematical model in the form of coupled partial differential equations is established. Later, this scheme of partial differential equations is transmuted into ordinary differential equations and then solved numerically. The numerical statistics of the problem are obtained by using a shooting technique in conjunction with the bvp4c MATLAB built-in program. The outcomes of density variation parameter ( m ), parameter of magnetic force ( S ), magnetic Prandtl number ( γ ), and Prandtl number (Pr) on temperature, current density, and velocity profiles are depicted in a graphical manner combined with their physical aspects. The uniqueness of this most recent procedure is claimed with a reason where the main attributes of the heat and fluid flow are driven under the action of temperature-dependent density mainly. From the closed observation of the density variable ( m ), for missing boundary conditions, the skin friction is increased..

Disentangling seasonal effects of environmental variability and population density on life-history traits in a capital breeder.

High-latitude environments are characterised by strong seasonality, with resident animals experiencing a very short plant-growing season for reproduction and acquisition of resources before the long and demanding winter. These seasonal fluctuations in food availability are likely to affect density-dependent processes, with density-dependent food limitation expected to be stronger outside the plant-growing season. Density dependence and environmental variability can have both direct and indirect effects on reproductive success through their influence on important indicators of individual quality, such as body mass. Untangling the direct and indirect effects of environmental factors and population density on life-history tactics is fundamental for understanding population and food-web dynamics. We developed a mechanistic path model to quantify the relative importance of direct and indirect effects of density dependence and environmental variability on body mass and reproductive success of female reindeer. Long-term individual measurements before and after lactation allowed quantifying simultaneously the direct negative effect of reproductive success on autumn body mass and the strong positive seasonal covariation among the individuals' body mass measurements. This emphasises the co-occurrence of a cost of reproduction and individual heterogeneity. We show that the estimated impact of density dependence on female body mass at the end of the summer is only 25% of the impact of density dependence during winter, as failed reproduction induced by low spring body mass leads to a large compensatory growth over summer. While such a pattern is expected, our estimates provide a unique and robust quantification of its importance. This result challenges the use of body mass data of adult individuals harvested in autumn when studying temperate large herbivores, as density dependence during winter and compensatory adjustments of reproductive effort may not be revealed without considering body mass both before and after lactation.

Electrochemically Promoted Activation of Light Alkanes at Ambient Conditions.

The electrochemical activation of light alkanes into value-added products represents a promising pathway for sustainable chemical synthesis and the storage of renewable energy. In this study, we introduce an electrochemically promoted system that employs copper plates as electrode and oxygen as oxidant, capable of converting ethane into ethylene and acetic acid with production rates of 6.9 and 6.2 µmol·cm-2Cu·h-1, respectively, with a combined selectivity exceeding 92%, under ambient conditions. Additionally, this system can convert propane to propylene at a rate of 11.6 µmol·cm-2Cu·h-1, with selectivity reaching up to 86%. A 10-hour run with ethane demonstrates consistent production of ethylene and acetic acid, with a sustained selectivity above 96% and achieving an acetic acid concentration of 19 mM. In situ spectroscopic analysis reveals the active surface and a critical reaction intermediate. Combining with partial pressure dependence study and Density Functional Theory (DFT) calculations, we propose a potential reaction mechanism involving the competitive adsorption of oxygen and alkane producing an alkyl group as a key reaction step in the reaction process.

Modeling of Power Generation and Acid Recovery in an Analogous Process of Reverse Electrodialysis.

The feasibility of an analogous reverse electrodialysis (RED) process for power generation and acid recovery from acidic waste streams in the steel industry is investigated in this study. A comprehensive model was established to simulate the transport phenomena and power generation, which was validated through experimental data. The simulated operation time was 3 h, during which an acid recovery rate of 41.7% was achieved, and the maximum output power density reached 30.37 μW·cm-2. The results demonstrated a strong dependence of output power density on the acid concentration, with a linear relationship within the tested range of 1.0-3.0 mol·L-1 HCl. An optimal flow rate range was identified that maximized power output, with the best value of 90 mL∙min-1. The differences in energy harvesting between the traditional acid diffusion dialysis process and our analogous RED process were demonstrated via simulation. The importance of system electroneutrality in driving ion migration and forming ionic currents was crucial for effective power generation. The analogous RED process is a promising solution for efficient acid recovery and power generation from industrial acid waste, offering a sustainable treatment approach.

Development of a model of power-linear conversion of digital images for dark tones

The object of research is the technological process of digital image processing using power transformation in pre-printing processes. A significant problem in preparing an image for printing is the phenomenon of posterization, which distorts the image and limits the possibilities of power transformation for correcting dark areas of the image. This is a disadvantage of power transformation, which is that at power indicators (r<0.45) and (r>1.5) power transformation is too sensitive to changes in black levels. The mathematical model of power-linear transformation of images for dark tones has been improved, which, unlike the known ones, involves the summation of power and linear transformation and includes a simulator of power-linear transformation of images. Taking into account the improved model, gradation characteristics, optical density dependences and contrast sensitivity were obtained, which quantitatively assess the perception of images by the human visual system. The validity of the improved model was verified by mathematical modeling using object-oriented programming and the MATLAB:Simulink software package. The results of mathematical modeling indicate that the development of the mathematical model allowed to further expand the possibilities of image correction. This is due to the fact that the length of the discrete gradation characteristics is 3–4 levels, which are not noticed by the human visual system (posterization is eliminated). The proposed model has significant advantages over image conversion methods used in printing. In particular, it expands the range of visual perception of images, eliminates the phenomenon of posterization, provides the ability to change (stretch and compress) contrast within wide limits. At the same time, it expands the functionality of power-law image conversion, and accordingly provides an increase in image quality when preparing it for printing. The results of the conducted research are recommended to be used at the stage of preparing images for printing and in workflows by operators and technologists.

Well-posedness of slightly compressible Boussinesq’s flow in Darcy–Bénard problem

In the present article, we show the existence, uniqueness, and behavior in time of solutions to the Darcy–Bénard problem for an extended-quasi-thermal-incompressible fluid (extended Darcy–Bénard problem) uniformly heated from below, modeling the phenomenon of thermal convection in porous media. First and foremost, for the sake of a more realistic description of the phenomenon under analysis, we here assume the fluid’s density to depend on pressure and temperature, unlike the classical problem where the density is solely a function of temperature. This new constitutive law for the density, proposed by Guoin and Ruggeri in 2012, arises as a necessary requirement for the thermodynamic consistency of the model and introduces a slight compressibility making the model more closely aligned with reality. Moreover, the dependence of the fluid density on both temperature and pressure fields, from the mathematical viewpoint, adds an interesting challenge, requiring a new approach for its resolution. The well-posedness results establish a foundation for further analyses of the hydrodynamic stability properties of the solutions of the extended Darcy–Bénard problem, with particular regard to the effect of compressibility factor, which has great interest in applications.

Half-metallicity and structural properties of low-concentration Fe-doped SrS alloys: a first-principles study

Present research reveals the doping effect on physical properties of Sr1-xFexS by employing ab-initio calculations. The negative formation energy and optimization outcomes exhibit the stability of the Sr1-xFexS alloys with ferromagnetic phase. Spin dependent band structure (BS) and density of states (DOS) interpret that Sr1-xFexS revealed half metallic ferromagnetic (HMF) nature at 6.25% and 12.5% of Fe doping while metallic character is revealed at 25% concentration of dopant. Spin-up state of Sr0.9375Fe0.0625S and Sr0.8750Fe0.1250S depicts semiconductive behavior with bandgap value of 2.01/2.33 eV, correspondingly, while metallic in spin-down channel. The magnetism in the system is mainly originated because of Fe-d state that further confirmed from magnetic spin density. The total magnetic moments are 4.001, 7.9889, 16.0180 (µΒ) for 6.25%, 12.5% and 25% doping, respectively. Furthermore, optical features are investigated to explore the role of concentration on the response of alloys to incident light (0-10 eV). The ε1(0) value are 13.4, 26.9, 70.1 for Sr0.9375Fe0.0625S, Sr0.8750Fe0.1250S and Sr0.75Fe0.25S, respectively. The maximum absorption exists within of 3.4-7.89 eV for the studied compounds that make them suitable material for UV optoelectronic devices. Thus, the investigated alloys can be employed for spintronic and optical device usages.

Intra- and interspecific competition between glyphosate-resistant and susceptible junglerice (Echinochloa colona) populations and soybean

Abstract Herbicide-resistant weeds demand particular attention in the selection of management strategies, considering the characteristics and fitness differences between susceptible and resistant plants. This study aimed to analyze two heterogeneous junglerice populations, glyphosate-susceptible (EC-S) and glyphosate-resistant (EC-R), derived from field-collected seeds, to quantify the productivity of EC-S and EC-R, to analyze the impact of soybean plants, and to evaluate density dependence. Experiments were conducted in a growth chamber using plastic pots, combining three factors: junglerice density (2, 4, and 8 plants pot⁻¹), the proportion of EC-S and EC-R (100% EC-S, 50% EC-S:50% EC-R, 100% EC-R), and soybean density (0 and 1 plant pot⁻¹). One-leaf junglerice seedling and soybean seeds were planted in plastic pots. After 65 days, plant height (PLH), total number of tillers (TIL), seed number (SEN), and seed weight (SEW) per plant, weight of 100 seeds (HSW), and aboveground dry matter (ADM) were measured. The variables measured were primarily affected by junglerice density and the presence of soybean. Vegetative and reproductive structures of EC-S and EC-R exhibited strongly density-dependent patterns. One soybean plant increased (p<0.05) junglerice productivity at low densities but had no effect at high densities (8 plants pot⁻¹). Mostly EC-S and EC-R showed the same competitive ability. However, EC-S presented a higher index of competitive ability than EC-R in SEN and SEW at lower densities with a soybean plant. A resource complementarity (RYT∼1) between EC-S and EC-R was observed (p<0.05), regardless of the presence of the crop. These results demonstrate that, even in the absence of glyphosate, fitness differences favor heterogeneous resistant populations. This highlights the inherent adaptive advantage of resistant populations and, considering the extensive reliance on glyphosate in current production systems underscores the urgent need for integrated weed management strategies to mitigate the evolution and spread of resistant populations.

The Massive and Distant Clusters of WISE Survey. XII. Exploring X-Ray Active Galactic Nuclei in Dynamically Active Massive Galaxy Clusters at z ∼ 1

Abstract We present an analysis of the cluster X-ray morphology and active galactic nucleus (AGN) activity in nine z ∼ 1 galaxy clusters from the Massive and Distant Clusters of WISE Survey observed with Chandra. Using photon asymmetry (A phot) to quantify X-ray morphologies, we find evidence that the four most dynamically disturbed clusters are likely to be mergers. Employing a luminosity cut of 7.6 × 1042 erg s−1 to identify AGNs in the 0.7–7.0 keV region, we show that the majority of these clusters host excess AGNs compared to the local field. We use the model of cumulative number counts ( log N − log S ) to predict AGN incidence in cluster isophotes under this luminosity cut. Our analysis finds evidence (at >2σ) of a positive correlation between AGN surface densities and photon asymmetry, suggesting that a disturbed cluster environment plays a pivotal role in regulating triggering of AGNs. Studying AGN incidence in cluster X-ray isophotes equivalent in area to 1.0r 500, we find that the AGN space density inversely scales with cluster mass as ∼ M − 0 . 5 − 0.18 + 0.18 at the 3.18σ level. Finally, when we separately explore the cluster mass dependence of excess AGN surface density in disturbed and relaxed clusters, we see tentative evidence that the two morphologically distinct subpopulations exhibit diverging trends, especially near the outskirts, likely due to cluster merger-driven AGN triggering/suppression.

Hybrid model of hydrogen thermal desorption from structural materials

To solve problems of hydrogen power engineering, there is an intensive search for materials for hydrogen storage. Thermal desorption spectrometry (TDS) is one of the effective experimental methods for studying the interaction of structural materials with hydrogen isotopes. A sample (we consider a thin plate made of a material with metallic properties) pre-saturated with dissolved atomic hydrogen is heated relatively slow in a vacuum chamber. The degassing flux is registered using a mass spectrometer. The spectrum is the dependence of the desorption flux density from a two-sided surface of the sample on the current temperature. Quite often, several local peaks are registered on the spectrum. Traditionally, this is associated with the reversible capture of various kinds of traps (inhomogeneities of the material) with different binding energies. However, numerical experiments on models with dynamic boundary conditions describing the dynamics of surface concentrations show the possibility of a different scenario. The following scheme is possible: The first peak occurs when hydrogen leaves the surface and the subsurface volume. Then, a large concentration gradient is formed at the surface. For this reason, and during continued heating, diffusion influx from the volume is significantly activated, which leads to the next peak of desorption. Recommendations on how to distinguish degassing scenarios corresponding to these essentially different physicochemical reasons are given. This is fundamentally important for the correct recalculation of modeling results from laboratory samples to real constructions. The hybrid thermal desorption model can be considered as a computational algorithm for solving a partial differential system using an approximation by an ODE system (but this is not a straight-line method).

Sensing of cyanide ion by tweaking the proton transfer.

Sensing of cyanide ion by tweaking the proton transfer.

ANALYSIS OF THE EFFECT OF THE B3Y-FETAL POTENTIAL ON ENERGY NEAR THE COULOMB BARRIER FOR THE 9Ве+12С SYSTEM

The experimental data of the elastic scattering process of the 9Ве+12С nuclear system were analyzed from the point of view of microscopic theory in energy near the Coulomb barrier. The new Botswana 3-Yukawa -Fetal potential, created in a variational approach with lower-order constraints on two body matrices, was first used for the 9Ве+12С system as a real part of the optical potential. In the double folding model, density-dependent parameters were introduced into the nucleon density distribution formula, and they were applied to the Botswana 3-Yukawa - Fetal and Michigan 3-Yukawa - Paris potentials based on effective nucleon-nucleon interactions. As a result, modified real microfolding potentials were created. The results of a semi-microscopic analysis calculated on the basis of new microfolding potentials were presented. The uniqueness of the research lies in the calculation of density-dependent parameters based on the incompressibility coefficient, which characterizes the saturation properties of the nuclear medium. The equations of state of the elastic scattering process were formulated at the saturation density (ρ0=0.17 fm-3), determined from the density dependence of the nuclear binding energy. The analysis results allow for a more accurate determination of nuclear properties and enhance the saturation properties of the nuclear medium. The efficiency of the new real potential was determined from a microscopic perspective, and the optimal parameters of the optical potential were found.

Should Regional Species Loss Be Faster or Slower Than Local Loss? It Depends on Density-Dependent Rate of Death.

Assessment of the rate of species loss, which we also label extinction, is an urgent task. However, the rate depends on spatial grain (average area A) over which it is assessed-local species loss can be, on average, faster or slower than regional or global loss. Ecological mechanisms behind this discrepancy are unclear. We propose that the relationship between extinction rate and A is driven by a classical ecological phenomenon: density-dependent mortality. Specifically, we hypothesize that (i) when per-individual probability of death (P death) decreases with the number of individuals in a region N (i.e., negative density dependence), per-species extinction rate (Px) should be high at regional grains and low locally. (ii) In contrast, when P death increases with N (i.e., positive density dependence), Px should be low regionally but high locally. (iii) Total counts of extinct species (Ex) should follow a more complex relationship with A, as they also depend on drivers of the species-area relationship (SAR) prior to extinctions, such as intraspecific aggregation, species pools, and species-abundance distributions. We tested these hypotheses using simulation experiments, the first based on point patterns and the second on a system of generalized Lotka-Volterra equations. In both experiments, we used a single continuous parameter that moved between the negative, zero, and positive relationship between P death and N. We found support for our hypotheses, but only when regional species-abundance distributions were uneven enough to provide sufficiently rare or common species for density dependence to act on. In all, we have theoretically demonstrated a mechanism behind different rates of biodiversity change at different spatial grains, which has been observed in empirical data.