Density Dependence Research Articles

Effects of density dependence in growth and natural mortality on FMSY and maximum sustainable yield

Abstract In fisheries management, it is generally assumed that density-dependent processes are confined to the pre-recruit stage of a fish. Consequently, current calculations of fishing mortality reference points include density dependence (DD) solely in recruitment dynamics. However, several studies have reported the importance of DD in growth and natural mortality (M). In this study, we tested the effect of DD on estimates of fishing mortality producing maximum sustainable yields (FMSY), comparing these estimates to those resulting from constant growth and M. We simulated fish populations with a wide range of life-history traits (LHTs), applying either constant or density-dependent growth and M and derived FMSY for each stock. Results showed that including DD in growth and M led to higher FMSY and often also higher yield estimates (MSY). The effect of DD was found to be greater in growth than in M. Additionally, FMSY estimates derived from surplus production models fitted to generated stocks with density-dependent growth and/or M were generally closer to true FMSY, compared to those from age-based long-term predictions assuming constant growth and M. However, due to the inherent uncertainties in estimates of stock dynamics and biological reference points (BRPs), caution is suggested before implementing DD in FMSY calculations. Equilibrium yield curves relating production to stock size were right-skewed, shape parameters from production models were slightly below 1 for scenarios assuming constant growth and M, but declined to 0.5 with increasing DD.

A multifrequency study of sub-parsec jets with the Event Horizon Telescope

The 2017 observing campaign of the Event Horizon Telescope (EHT) delivered the first very long baseline interferometry (VLBI) images at the observing frequency of 230,GHz, leading to a number of unique studies on black holes and relativistic jets from active galactic nuclei (AGN). In total, eighteen sources were observed, including the main science targets, Sgr,A* and M,87, and various calibrators. Sixteen sources were AGN. We investigated the morphology of the sixteen AGN in the EHT 2017 data set, focusing on the properties of the VLBI cores: size, flux density, and brightness temperature. We studied their dependence on the observing frequency in order to compare it with the Blandford-K"onigl (BK) jet model. In particular, we aimed to study the signatures of jet acceleration and magnetic energy conversion. We modeled the source structure of seven AGN in the EHT 2017 data set using linearly polarized circular Gaussian components (1749+096, 1055+018, BL,Lac, J0132--1654, J0006--0623, CTA,102, and 3C,454.3) and collected results for the other nine AGN from dedicated EHT publications, complemented by lower frequency data in the 2-86,GHz range. Combining these data into a multifrequency EHT+ data set, we studied the dependences of the VLBI core component flux density, size, and brightness temperature on the frequency measured in the AGN host frame (and hence on the distance from the central black hole), characterizing them with power law fits. We compared the observations with the BK jet model and estimated the magnetic field strength dependence on the distance from the central black hole. Our observations spanning event horizon to parsec scales indicate a deviation from the standard BK model, particularly in the decrease of the brightness temperature with the observing frequency. Only some of the discrepancies may be alleviated by tweaking the model parameters or the jet collimation profile. Either bulk acceleration of the jet material, energy transfer from the magnetic field to the particles, or both are required to explain the observations. For our sample, we estimate a general radial dependence of the Doppler factor δ ∝ r^ ≤0.5 . This interpretation is consistent with a magnetically accelerated sub-parsec jet. We also estimate a steep decrease of the magnetic field strength with radius B ∝ r^ hinting at jet acceleration or efficient magnetic energy dissipation.

Symmetry energy effect on hot nuclear matter and proto-neutron stars

Abstract We examine the effects of symmetry energy on proto-neutron stars (PNSs) by employing equation of state (EOS) described by the relativistic mean-field (RMF) model.
The thermal properties of dense matter and the bulk properties of PNSs are investigated under the assumptions of isothermy, isentropy, and fixed lepton fractions.
The polytropic index is calculated at finite temperature, 
revealing a negative correlation with the PNS maximum mass that the EOS can support.
The properties of PNSs during the heating and cooling stages along their evolution line are explored under different combinations of lepton fraction and entropy.
We investigate the correlation between the symmetry energy slope $L$ and the properties of PNSs. As $L$ increases, the PNS radius also increases; however, this effect diminishes with a growing lepton fraction for the isentropic case.
These results indicate that the nuclear symmetry energy and its density dependence play crucial roles in determining the properties of PNSs and their evolution stages.

Features of strangeness production in pp and heavy-ion collisions

Based on existing experimental data for A−A collisions starting from the Alternating Gradient Synchrotron energies to those of the CERN Large Hadron Collider, various systematics related to strange hadrons and antihadrons are presented. As in the case of pions, kaons, and protons, the ratio between the average transverse momentum and the square root of the total particle multiplicity per unit rapidity and unit transverse overlap area (〈pT〉/〈dN/dy〉/S⊥) decreases with collision energy and centrality supporting the predictions of the color glass condensate and percolation approaches. The dependencies on 〈dN/dy〉/S⊥ of the slope and offset extracted from the 〈pT〉-particle mass correlation and of the average transverse expansion velocity and kinetic freeze-out temperature, parameters obtained from Boltzmann-Gibbs Blast-Wave fits of pT spectra for strange hadrons, are compared with those for pions, kaons, and protons. The detailed study of the entropy density (〈dN/dy〉/S⊥) dependence of the ratio of strange hadron yields per unit rapidity to the total particle multiplicity per unit rapidity (YS/〈dN/dy〉) at different collision energies and centralities reveals the necessity to study strange hadrons and antihadrons separately. The correlations YS/〈dN/dy〉−〈dN/dy〉/S⊥ for single- and multistrange antihadron yields, as a function of the fireball size, are discussed. The YS/〈dN/dy〉−〈dN/dy〉/S⊥ correlations for combined and separated strange hadron species, at different centralities, clearly show a maximum in the region where a transition from baryon-dominated matter to meson-dominated matter occurs. Comparison with pp experimental data reveals another similarity between pp and Pb-Pb collisions at CERN Large Hadron Collider energies. To facilitate a possible comparison with theoretical approaches, the different correlations are either fitted with suitable functions or the corresponding experimental data are provided. Published by the American Physical Society 2025

Complementary Reducing Agents are Responsible for Temporally Distinct Nucleation and Growth Phases During the Polyol Synthesis of Ag Nanocubes

AbstractEthylene glycol or one of its oxidation products are believed to serve as reducing agents in the shape‐controlled synthesis of Ag nanocubes (NCs) by the polyol process. The identity of end‐groups of polyvinylpyrrolidone (PVP) impacts shape control with alcohol and aldehyde moieties serving as a primary Ag reducing agent. We explored the role of PVP end‐groups in the polyol process by measuring the dependence of particle number density of Ag NCs produced on the initial concentration(s) of Ag and PVP using small angle x‐ray scattering and statistically large particle size distributions analyzed by scanning electron microscopy. The number density of Ag NCs is strongly dependent on the starting concentration of PVP chains demonstrating PVP end‐groups play an important role in the nucleation of NCs. The concentration of Ag+ is 2 orders of magnitude higher than the end‐groups suggesting ethylene glycol must participate in the reduction of Ag+ during growth. Perturbation experiments and analysis of resultant particle size distribution reveal nucleation is fast relative to growth of NCs, reinforcing the synergy between PVP end‐groups and ethylene glycol. The evidence demonstrates PVP end‐groups and ethylene glycol are tandem reducing agents operative in temporally distinct phases of the polyol synthesis of Ag NCs.

Modeling the effect of substituents on the electronically excited states of indole derivatives.

A proper understanding of excited state properties of indole derivatives can lead to rational design of efficient fluorescent probes. The optically active and excited states of a series of substituted indoles, where a substituent was placed on position four, were calculated using equation of motion coupled cluster and time dependent density functional theory. The results indicate that most substituted indoles have a brighter second excited state corresponding to experimental absorption maxima, but a few with electron withdrawing substituents absorb more on the first excited state. Absorption on the first excited state may increase their fluorescence quantum yield, making them better probes. Electronic structure methods were found to predict the energies of the systems with electron withdrawing substituents more accurately than those with electron donating substituents. The excited states of both states correlated well with electrophilicity, similar to the experimental trends for the absorption maxima. Overall, these computational studies indicate that theory can be used to predict excited state properties of substituted indoles, when the substituent is an electron withdrawing group.

Exploration of potential-limited protocols to prevent inefficiencies in Li-O2 batteries during charge.

Metal-air batteries are promising energy storage systems with high specific energy density and low dependence on critical materials. However, their development is hindered by slow kinetics, low roundtrip efficiency, deficient capacity recovery, and limited lifetime. This work explores the effect of cycling protocols on the lifetime of Li-O2 cells, and the interplay between electrolyte composition and the upper cut-off voltage during charge. Our results suggest that constant-current-constant-voltage (CCCV) protocols accommodate the slower kinetics at the end of charge in Li-O2 cells better than the constant-current (CC) protocols majorly used in the field. These results suggest that CCCV protocols should be standardised to assess performance improvements in Li-O2 cells.

Binder jet 3D printing of 316L stainless steel: A Taguchi analysis of the dependence of density and mechanical properties on the printing parameters

Binder jet 3D printing of 316L stainless steel: A Taguchi analysis of the dependence of density and mechanical properties on the printing parameters

Three-dimensional time-dependent water flows with constant non-vanishing vorticity and depth dependent density

Three-dimensional time-dependent water flows with constant non-vanishing vorticity and depth dependent density

Climate change could amplify weak synchrony in large marine ecosystems

Climate change is increasing the frequency of large-scale, extreme environmental events and flattening environmental gradients. Whether such changes will cause spatially synchronous, large-scale population declines depends on mechanisms that limit metapopulation synchrony, thereby promoting rescue effects and stability. Using long-term data and empirical dynamic models, we quantified spatial heterogeneity in density dependence, spatial heterogeneity in environmental responses, and environmental gradients to assess their role in inhibiting synchrony across 36 marine fish and invertebrate species. Overall, spatial heterogeneity in population dynamics was as important as environmental drivers in explaining population variation. This heterogeneity leads to weak synchrony in the California Current Ecosystem, where populations exhibit diverse responses to shared, large-scale environmental change. In contrast, in the Northeast U.S. Shelf Ecosystem, gradients in average environmental conditions among locations, filtered through nonlinear environmental response curves, limit synchrony. Simulations predict that environmental gradients and response diversity will continue to inhibit synchrony even if large-scale environmental extremes become common. However, if environmental gradients weaken, synchrony and periods of large-scale population decline may rise sharply among commercially important species on the Northeast Shelf. Our approach thus allows ecologists to 1) quantify how differences among local communities underpin landscape-scale resilience and 2) identify the kinds of future climatic changes most likely to amplify synchrony and erode species stability.

Density-dependent flow generation in active cytoskeletal fluids

The actomyosin cytoskeleton, a protein assembly comprising actin fibers and the myosin molecular motor, drives various cellular dynamics through contractile force generation at high densities. However, the relationship between the density dependence of the actomyosin cytoskeleton and force-controlled ordered structure remains poorly understood. In this study, we measured contraction-driven flow generation by varying the concentration of cell extracts containing the actomyosin cytoskeleton and associated nucleation factors. We observed continuous actin flow toward the center at a critical actomyosin density in cell-sized droplets. The actin flow exhibited an emergent oscillation in which the tracer advection in the bulk solution periodically changed in a stop-and-go fashion. In the vicinity of the actomyosin density where oscillatory dynamics occur, the velocity of tracer particle motion decreases with actomyosin density but exhibits superdiffusive motion. Furthermore, the increase or decrease in myosin activity causes the oscillatory flow generation to become irregular, indicating that the density-dependent flow generation of actomyosin is driven by an interplay between actin density and myosin force generation.

Free Carrier Auger-Meitner Recombination in Monolayer Transition Metal Dichalcogenides.

Microscopic many-body models based on inputs from first-principles density functional theory are used to calculate the carrier losses due to free carrier Auger-Meitner recombination (AMR) processes in Mo- and W-based monolayer transition metal dichalcogenides as a function of the carrier density, temperature, and dielectric environment. Despite the exceptional strength of Coulomb interaction in the two-dimensional materials, the AMR losses are found to be similar in magnitude to those in conventional III-V-based quantum wells for the same wavelengths. Unlike the case in III-V materials, the losses show nontrivial density dependencies due to the fact that bandgap renormalizations on the order of hundreds of millielectronvolts can bring higher bands into or out of resonance with the optimal energy level for the AMR transition, approximately one bandgap from the lowest band. Similar nontrivial behaviors are found for the dependencies of AMR on the temperature and dielectric screening.

Density-dependent distributions of hosts and parasitoids resulting from density-independent dispersal rules: implications for host–parasitoid interactions and population dynamics

BackgroundThe distribution of hosts and parasitoids across patches is a key factor determining the dynamics of host-parasitoid populations. To connect behavioral rules with population dynamics, it is essential to comprehend how individual-level dispersal behavior influences the distribution of individuals. Typically, a simple deterministic model has been used to describe this connection. This study explicitly derived the relationship between individual-level dispersal behavior and the distribution of individuals across patches, contrasting it with the conventional deterministic model.MethodsA stochastic individual-based model was developed from a widely used deterministic host–parasitoid population model. Individual-level dispersal rules were simulated in the stochastic model without assuming the resulting distributions. The models assume that the dispersal of hosts and parasitoids is independent of conspecific density. The deterministic model can be seen as an approximation of the stochastic model, describing the outcomes of stochastic processes as their expected patterns. In addition to describing the relationship between dispersal behavior and distribution across patches, its consequences for population dynamics were also examined.ResultsThe stochastic model revealed that the distribution of individuals among patches varies with the number of dispersing conspecifics, whereas the deterministic model assumes independence from conspecific density, indicating that the deterministic model fails to capture the outcomes of stochastic dispersal. The resulting density-dependent distributions of hosts and parasitoids lead to other density-dependent interactions between them, such as density-dependent parasitism risk for hosts and density-dependent searching efficiency for parasitoids, ultimately affecting population dynamics. For instance, while aggregation of parasitoids is stabilizing in the deterministic model, it can be both stabilizing and destabilizing in the stochastic model.ConclusionsThe stochastic model revealed that density-dependent distributions of hosts and parasitoids emerge when individuals disperse in a density-independent manner, significantly impacting existing host-parasitoid theory, which assumes density-independent distributions. To address this, the implications of emerging density dependencies for well-known results, such as the pseudointerference of parasitoids and the CV2 > 1 rule, were discussed. Explicitly considering individual-level dispersal behavior is essential for understanding host–parasitoid interactions and population dynamics.

Seasonal and Altitude Dependence of Thermospheric Metastable Helium Densities Measured by Fluorescence Lidar

AbstractAirglow originating from metastable helium He(S) at 1,083 nm has been used to study the upper thermosphere since its discovery in 1959, yielding insights into, for example, solar EUV intensities and thermospheric photoelectron densities. For over 6 decades, these measurements were made passively, relying on solar illumination of the He(S) layer to produce a detectable signal, resulting in a column integration of the He(S) layer. Recently, the first height‐resolved measurements of He(S) density were made by fluorescence lidar, opening a new window for studying the upper thermosphere. We report on a series of 51 measurements by this instrument spanning an entire winter season and extending to an altitude of 1,000 km, revealing a broad He(S) layer that peaks at higher altitudes than previously expected.

Antimicrobial, and Antitubercular Evaluation with ADME and Molecular Docking Studies and DFT Calculatıons of (Z)-3-((1-(5-amino-1,3,4-thiadiazol-2-yl)-2-Phenylethyl)imino)-5-nitroindolin-2-one Schiff Base

(Z)-3-((1-(5-Amino-1,3,4-Thiadiazol-2-yl)-2-Phenylethyl)İmino)-5-nitroindolin-2-one Schiff Base compound (ATSB) have lately gained popularity, so the concept that these compounds should be researched has been highlighted. ATSB molecule, a unique Schiff base complex, was selected for molecular modeling research for publication in the literature. Initially, dependent density functional theory (DFT) computations were performed on ATSB molecule (geometry optimization, HOMO-LUMO, MEPS maps, dipole moment calculations, NBO analysis, and Mulliken Atomic Charges). Additionally, ADME analyzes have been carried out for the ATSB molecule and the color regions are given separately. Schiff bases have been shown to have an important role in antibacterial and antituberculosis medication illness and drug repair. Finally, in our investigation, molecular docking analysis ments were performed individually for ATSB molecule with two distinct enzymes (5V3X and 5V3Y), docking scores and receptor models have been given.

Great Lakes mallard population dynamics

AbstractBreeding mallard (Anas platyrhynchos) populations in the Great Lakes region (Michigan, Minnesota, Wisconsin, USA) declined by >40% between 2000–2022 based on abundance data collected during spring aerial surveys. Mallards are an important waterfowl species in this region, where an estimated 60–80% of the mallard harvest is composed of locally banded birds. Extensive population monitoring datasets are available for mallards, presenting an opportunity to address complex questions such as estimating productivity at large spatial and temporal scales, identifying the effects of harvest on mallard demography, quantifying mechanisms for harvest compensation, and integrating multiple datasets to quantify the demographic drivers of population change. Our objective was to simultaneously examine factors affecting demographic parameters and their relative contribution to Great Lakes mallard population dynamics. We used 32 years of banding, band recovery, and aerial survey data collected for mallards from Michigan and Wisconsin to develop an integrated population model (IPM). We used age ratios at banding to estimate productivity, band recoveries from hunter‐harvested birds to estimate annual survival and cause‐specific mortality (i.e., harvest or non‐hunting), and modeled abundance using aerial survey and demographic parameter estimates from 1991–2022. The IPM results indicated the decline in Great Lakes mallard abundance was caused by increased non‐hunting mortality and a decline in productivity. Productivity varied spatially but temporally declined with the loss of Conservation Reserve Program area. Moreover, our productivity assessment provided evidence of density dependence in reproduction. Non‐hunting mortality was 3.5–6.7 times and 1.3–4.2 times greater than harvest mortality for adult and juvenile female mallards, respectively, indicating environmental factors during spring and summer, not harvest, most greatly influenced annual mortality for female mallards. Our IPM reduced uncertainty in the factors affecting Great Lakes mallard population dynamics and indicated management actions that address non‐hunting mortality and productivity would be most effective in increasing Great Lakes mallard abundance.

Capturing Broadband Spectral Characteristics of Moderate-Size Earthquakes Using Nearby Recordings: A Case Study of 42 Mw 4.0–5.4 Ridgecrest Earthquakes

ABSTRACT Characterizing the information in earthquake source spectra requires three measures: seismic moment M0, apparent stress σa, and stress parameter ΔσB. We estimate σa and ΔσB for 42 Ridgecrest, California, earthquakes (4.0≤Mw≤5.4), using three-component records within 50 km to minimize path effects. We analyze the data in both the time and frequency domains. We account for the depth dependence of source velocity and density and calibrate the results using observations at a rock site. Time-domain analysis for σa reveals significant apparent crustal attenuation (∝r−1.6, in which r is the centroid distance) and large site amplifications. In the frequency domain, we estimate near-surface impedance as a function of frequency at each station. We conduct a grid search with F-tests to constrain a frequency-dependent crustal Q model (Q(f)=q0fα) and site attenuation constant κ0 for each station, assuming a ω−2 model. The global best model has q0=60, α=0.675, with κ0 ranging from 0.01 to 0.05 s. σa and ΔσB were estimated using corrected observations. The σa values from both time- and frequency-domain analyses are in excellent agreement, ranging from 0.09 to 2.7 MPa with a geometric mean of 0.59 MPa. ΔσB ranges from 0.27 to 6.9 MPa with a geometric mean of 1.8 MPa. The ratio of ΔσB and σa (∼3.0) suggests the source spectrum in this magnitude range is close to a single-corner spectral model. We find both σa and ΔσB increase quickly with centroid depth that cannot be explained with depth-dependent crustal attenuation. Geometric mean values for σaF and ΔσB for earthquakes with centroid depths of ≥6 km are 0.92 and 2.91 MPa, respectively, approximately fourfold the values for earthquakes with centroid depths <6 km. Considering the significant impact to near-fault strong ground motion, the cause of this sharp transition deserves further investigation.

Long‐Term Declines in Body Size of the Invasive Rusty Crayfish (Faxonius rusticus) in Temperate Lakes

ABSTRACT Invasive species often experience phenotypic change during the invasion process. For example, many invasive species are larger in their non‐native than native ranges, but some invasive species experience body size declines with time since invasion. Mechanisms of these phenotypic changes are poorly known, likely due to a paucity of long‐term datasets and complex interactions among abiotic and biotic factors that affect body size over time. We use a long‐term dataset (1980–2020) in 17 lakes of Wisconsin, United States to investigate trends in body size for an invasive species, the rusty crayfish (Faxonius rusticus). We relate F. rusticus body size to crayfish relative abundance as catch‐per‐unit effort (CPUE) from baited trapping, as well as modelled lake temperatures and pelagic primary productivity, using a structural equation model (SEM). Our use of an SEM allowed us to investigate the direct effect of time on F. rusticus on body size, as well as indirect effects through factors like warming of lakes due to climate change. We found that F. rusticus body size has declined by 10% over the past four decades in our study lakes, from a mean of 36.6 mm total carapace length in 1980 to 32.8 mm in 2020. Faxonius rusticus individuals were larger when lakes were warmer, but the overall effect of time on declining F. rusticus body size was stronger than this predictor. Relative abundance as CPUE had no effect on F. rusticus body size, rejecting a role for density dependence in explaining adult body size of this invasive crayfish. Declining F. rusticus body sizes have accompanied population declines of this invasive crayfish in some Wisconsin lakes, and both trends provide potential for post‐invasion ecosystem recovery. As one example, smaller F. rusticus individuals may be less effective or active predators on fish nests. By contrast, declining F. rusticus body size may also create opportunities for serial or over‐invasion by future crayfish invaders, sustaining a need to discourage crayfish introductions to this region.

Eelgrass (Zostera marina) Recovery Affected by Disturbance Timing on Mechanically Harvested Oyster Culture Beds

Amid global seagrass declines and increasing human demands of coastal habitat, it is critical to mitigate the loss of seagrass habitat through understanding seagrass resilience following large-scale disturbance. Although seagrasses often respond to disturbance through increased sexual or asexual reproduction, past research on the cosmopolitan Zostera marina (eelgrass) is highly variable in terms of whether recovery occurs, and whether seeds or clonal growth is the primary contributor. In Willapa Bay, Washington state, we studied eelgrass recovery following large-scale disturbance on six adjacent oyster culture beds (~ 10,000 m2 in area) that were harvested using mechanical methods (i.e., dredging). We found that recovery potential and mode are heavily affected by the timing of disturbance. In the 200 and 400 days post-disturbance, beds disturbed during the early growing season (EGS; January–April) were estimated to have more than double the vegetative shoot density of beds disturbed during the late growing season (LGS; May–September). We also found a higher contribution of new shoots from seedlings following EGS relative to LGS disturbance, with up to 71% of shoots following EGS disturbance occurring from seedling origin. Consistent with eelgrass life history, spring seedling densities were positively affected by flowering shoot densities the previous summer. Clonal reproduction (i.e., branching) was negatively affected by a disturbance within the past 4 months, likely from physical damage, but also showed negative density dependence, meaning that higher branching rates were observed at lower shoot densities. Overall, this work emphasizes the importance of seedlings to seagrass recovery and demonstrates that Z. marina has higher recovery when disturbed (here by mechanical harvest of shellfish) during EGS versus LGS time periods. These findings provide straightforward guidelines for the management of anthropogenic disturbance on eelgrass beds to reduce permanent habitat loss and can also guide restoration efforts of eelgrass beds.

Polarization-induced two-dimensional hole gases in N-polar AlGaN/GaN heterostructures

We report the observation of two-dimensional hole gases (2DHGs) in N-polar AlGaN/GaN heterostructures grown on single-crystal GaN substrates by plasma-assisted molecular beam epitaxy. A systematic study varying AlGaN barrier thickness is performed. The presence of 2DHGs is confirmed by persistent p-type conductivity and high hole mobility observed in temperature-dependent Hall-effect measurements down to 10 K, and the dependence of 2DHG density on the AlGaN barrier thickness indicates its polarization induced origin. 2DHG with a sheet density of 7.5×1012 cm−2 shows a relatively high hole mobility of 273 cm2 V−1 s−1 at 10 K. Mobility model fit suggests that acoustic phonon scattering is the dominant scattering mechanism in the sub-room temperature region. This work indicates that the quality of N-polar 2DHGs is comparable to that of state-of-the-art metal-polar 2DHGs, contributing to a building block for potential high-quality N-polar p-channel devices.