Emergent colloidal currents across ordered and disordered landscapes

Many-particle effects in driven systems far from equilibrium lead to a rich variety of emergent phenomena. Their classification and understanding often require suitable model systems. Here we show that microscopic magnetic particles driven along ordered and defective lattices by a traveling wave potential display a nonlinear current-density relationship, which arises from the interplay of two effects. The first one originates from particle sizes nearly commensurate with the substrate in combination with attractive pair interactions. It governs the colloidal current at small densities and leads to a superlinear increase. We explain such effect by an exactly solvable model of constrained cluster dynamics. The second effect is interpreted to result from a defect-induced breakup of coherent cluster motion, leading to jamming at higher densities. Finally, we demonstrate that a lattice gas model with parallel update is able to capture the experimental findings for this complex many-body system.

Experimental testing of density- and season-dependent growth in vegetative Fucus aquaculture and modelling of growth over one year for different cultivation scenarios

In the Kiel Fjord, western Baltic Sea, an experimental culture of Fucus vesiculosus and Fucus serratus has been established in order to develop a sustainable method for biomass production of these species. The cultivation method includes the unattached rearing of fronds in drifting baskets and their vegetative reproduction by cutting of small vegetative apices. In this study, we performed culture experiments to measure growth rates with this method at different initial stocking densities (1–5 kg m−2) and during different seasons of the year. Using the results, we modelled growth over 1 year for different cultivation scenarios (different initial stocking densities (1–4.75 kg m−2) and harvest densities (1.25–5 kg m−2)) in order to identify optimal scenarios and estimate annual yields and the number of necessary harvests in these scenarios. Fucus vesiculosus showed a parabolic yield–density relationship with decreasing yields at high initial stocking densities (> 2.5 kg m−2). In contrast, F. serratus showed an asymptotic yield–density relationship with rather constant yields at high initial stocking densities. Both species showed a typical seasonal growth pattern with low growth rates during winter and high growth rates during summer; however, F. serratus seemed to be growth limited during summer which was not observed for F. vesiculosus. The modelling results reflected the results of the Density experiment: for F. vesiculosus, optimal cultivation scenarios were found for intermediate cultivation densities (initial stocking densities, 1.75–2.25 kg m−2; harvest densities, 3–4 kg m−2); for F. serratus, optimal cultivation scenarios included higher densities (initial stocking densities, 2.5–4 kg m−2; harvest density, 5 kg m−2). The model scenarios predicted maximal annual yields of 6.65–6.76 kg m−2 for F. vesiculosus and 6.88–6.99 kg m−2 for F. serratus. For both species, the number of harvests necessary to achieve these yields varied depending on the cultivation scenario from 2 to 6. Scenarios with only 1 harvest per year yielded slightly lower annual yields. We conclude that the modelling results offer a valid and helpful orientation for future efforts to produce Fucus species in commercial culture.

Relative density of United States forests has shifted to higher levels over last two decades with important implications for future dynamics

Tree size-density dynamics can inform key trends in forest productivity along with opportunities to increase ecosystem resiliency. Here, we employ a novel approach to estimate the relative density (RD, range 0–1) of any given forest based on its current size-density relationship compared to a hypothetical maximum using the coterminous US national forest inventory between 1999 and 2020. The analysis suggests a static forest land area in the US with less tree abundance but greatly increased timber volume and tree biomass. Coupled with these resource trends, an increase in RD was identified with 90% of US forest land now reaching a biologically-relevant threshold of canopy closure and/or self-thinning induced mortality (RD > 0.3), particularly in areas prone to future drought conditions (e.g., West Coast). Notably, the area of high RD stands (RD > 0.6) has quintupled over the past 20 years while the least stocked stands (RD < 0.3) have decreased 3%. The evidence from the coterminous US forest RD distribution suggest opportunities to increase live tree stocking in understocked stands, while using density management to address tree mortality and resilience to disturbances in increasingly dense forests.

Correlating the Durability Properties of Roller Compacted Concrete

Roller compacted concrete is the zero-slump concrete mixture, usually prepared at low cement content and low workability, and subjected to compaction by rollers to increase the density and improve the aggregate particles interlock. It is recommended for heavy duty pavement and can withstand harsh environment. Modeling the physical behavior of roller compacted concrete exhibits a quick and easy start to predict the future behavior of the material. In the present assessment, roller compacted concrete mixtures have been prepared in the laboratory using three percentages of Portland cement (10, 12, and 16) % to simulate low, medium, and high cement content from roller compacted concrete point of view. The mixtures were poured into the cylinder mold of 101.6 mm diameter and 116.4 mm height in five successive layers. Each layer had practiced 25 blows of the modified Proctor hammer with 4.5 kg weight, falling from 450 mm height. Specimens were withdrawn from the mold after 24 hours and cured for 28 days in a water bath at 20°C. Specimens were subjected to bulk density, absorption, and porosity determination. Test results were analyzed and modeled. It can be observed that the gradation of aggregates (dense or gap)does not exhibit a significant issue in the absorption-density relationship. However, Dense gradation exhibits lower porosity than gap gradation. It can be concluded that the obtained mathematical models may be implemented to predict the relationship between the durability parameters of roller compacted concrete in terms of porosity, absorption, and density with high coefficients of determination.

Dynamically Collected Local Density using Low-Cost Lidar and its Application to Traffic Models

This article demonstrates the use of traffic density observations collected dynamically in the vicinity of probe vehicles. Fixed position sensors cannot capture the longitudinal evolution of local traffic density in the corridor. In this research, dynamic traffic density observations were collected in a naturalistic driving setting that was free of any controlled experiment biases. Speed from global positioning system and space headway from a light detection and ranging module was collected on one arterial and one freeway segment, 2 and 4 mi long, respectively. The combined data frequency was approximately 3 Hz. Space headway was used to estimate the local density and consequently to identify the density of a specific location in a corridor. Besides, driver behavior was characterized using the relationship between instantaneous speed and local density under different regimes of the Wiedemann car-following model. Macroscopic traffic stream models were used to investigate the relationship between dynamically collected instantaneous speed and local density. Using the longitudinal evolution of density, precise local density across the corridor can be obtained along with the leader and follower trajectories. A method to identify driver behavior across density ranges was developed for different facility types using a microscopic relationship between instantaneous speed and local density. Overall driving behavior on the freeway segment can be represented by translating the instantaneous speed and local density relationship to macroscopic stream models.

A macroecological perspective on the fluctuations of exploited fish populations

The natural variability of fish populations is increased by exploitation, but the specific mechanisms driving this variability are still debated. We propose a macroscopic approach combining the size-density relationship and Taylor’s law to predict the temporal variance of exploited and unexploited fish populations. Using information from 11 years of fishery-independent abundance surveys, we showed that the body-size dependence of the variance of exploited (targeted) and unexploited (non-targeted or bycatch) fish populations can be accurately predicted. Targeted fish populations showed a variability that was 2 orders of magnitude greater than that of non-targeted fish populations. Such variability was explained solely by the higher relative abundance of the former, regardless of their specific trophic position, while aggregated community fluctuation was lower in a high trophic position group. This study showed the usefulness of the macroscopic approach to predict fish variability and fishing effect in the whole community. This approach is complementary to other modeling strategies and seems to be useful in tackling the problem of variability in population fluctuations of exploited fish, particularly in cases where specific details of the interacting species are lacking.

Structural, and Radiation Shielding Simulation of B2O3-SiO2-LiF- ZnO-TiO2 Glasses

Quaternary glasses with a 59B2O3-29SiO2-2LiF-(\(10-x\)) ZnO-\(x\)TiO2 composition using the melt-quench techniques were prepared. XRD examined the nature of prepared glasses. The FT-IR spectra was studied for the changes in the structure of these glasses. While the density is increased, the molar volume of the glass system is reduced. The velocities and elastic modulus of these glasses were experimentally and theoretically based on the Makishima-Mackenzie model evaluated. Besides, for the studied glasses, the radiation shielding efficiency was investigated by Phy-X/PSD and XCOM software. These glasses were found to have an abnormal attenuation, structural, and density relationship. The mass attenuation coefficient (µ/ρ), linear attenuation coefficient (LAC), half-value layer (HVL), tenth value layer (TVL), and effective atomic number (Zeff), of glasses, have been designed to simulate for gamma photon energies between 0.015 and 15 MeV. MAC values calculated using Phy-X/PSD and XCOM were compared and was observed in good agreement with the other.