Relative Density Difference Research Articles

A new modeling approach for microplastic drag and settling velocity

Understanding microplastics' (MPs') transport and settling behaviors in aquatic environments is crucial for devising effective management strategies. This study contributes a novel modeling framework to develop accurate and interpretable drag and velocity models for MPs using machine learning techniques. It achieves faster model creation and improved accuracy than traditional methods like theoretical analysis and data fitting. The framework demonstrates high predictive accuracy across different MP types (1D, 2D, 3D, and mixed), with a coefficient of determination CD = 0.86–0.95 for the drag models and CD = 0.92–0.95 for the velocity models. Compared with best-performing empirical approaches, the new drag models exhibit an average reduction in root mean square error (RMSE) by 59% and mean absolute error (MAE) by 62%. Similarly, the velocity models show a mean decrease in RMSE and MAE by 27% and 25%, respectively. Moreover, the framework outperforms commonly used symbolic regression methods, reducing errors by 18%–27%. The sensitivity analysis reveals that the relative density difference and the dimensionless diameter are essential for predicting the settling of all MP types, while the effective shape parameters vary across different MP categories. By providing accurate predictions of MPs' settling dynamics, this study offers insights for developing targeted mitigation strategies to reduce MPs' environmental impacts.

Study of the role of abyssal ocean stratification in the rearrangement of potential vorticity through the water column

Abstract. Observations of abyssal variability performed in the Ionian Sea (Mediterranean Sea) have revealed the presence of a dense, stable abyssal layer, whose thermohaline and dynamical properties changed drastically over a decade. Building upon these available observations, we aim to investigate the role that stratification can play in the transmission of vorticity throughout the water column to the abyss and, in turn, in the redistribution of energy stored in the deep sea, with a set of stationary states. A quasi-geostrophic level model equipped with four coupled layers, a free surface, and a mathematical artifice for parameterizing decadal time evolution has been considered, proving that the relative-thickness and relative-density differences among the layers are the two critical factors that determine the dynamical characteristics of this rearrangement. The variability in ocean stratification is a relevant aspect that can activate deep and intermediate dynamics, engaging in the propagation and stabilization of signals throughout the water column. This demonstrates the non-negligible active connection between the dynamics of the bottom layers and the surface. The theoretical framework and parameterization used are based on specific observations made in the Ionian Sea over the last decades but retain general applicability to all ocean basins that are characterized by the presence of a stratified, dense water mass in their deep and intermediate layers.

Microstructure and compressive behaviour of PLA/PHA-wood lattice structures processed using additive manufacturing

This study investigates the microstructure and compressive behaviour of PLA/PHA-wood lattice structures manufactured using fused filament fabrication (FFF). The primary objective is to evaluate the effects of defects, such as porosity and surface roughness, on the mechanical properties of these lattice structures. X-ray micro-tomography (XRT) and finite element analysis are employed to compare CAD models with real lattice structures, offering insights into defect-induced performance deviations. The novel approach integrates experimental and numerical methods to better understand damage accumulation in porous structures. The methodology includes uniaxial compression testing and image processing for microstructural characterization. Results reveal significant differences in relative density and stress concentration due to manufacturing defects. In particular, 3D printed lattice structures display typical cellular material behaviour with a primary bending deformation mechanism. X-ray tomography reveals that process-induced porosity generate stress heterogeneity, which is not captured from CAD-based model resulting in an overestimation of the stiffness. The study concludes that accounting for these defects can be quantified by shifting the target relative density to compensate lack of performance in 3D-printed lattice materials.

Effect of Deposit Scale on Mechanical Properties of In-Situ Alloyed CrCoNi Medium Entropy Alloys Formed by Directed Energy Deposition

Directed energy deposition (DED), as an additive manufacturing technology, has shown unique advantages in multi-material additive manufacturing and remanufacturing. In this study, two types in-situ alloyed CrCoNi medium entropy alloys that have thin-walled structures with different thicknesses (T1 and T2) were manufactured by the DED process, and the mechanisms of differences in relative density, microstructure, and mechanical properties at different heights were systematically analyzed. In terms of microstructure, the T1 and T2 samples along the building direction exhibit significant differences in crystallographic orientation, grain size, and dislocation density, which are related to the local temperature gradient differences caused by the scanning path and heat accumulation. In terms of mechanical properties at different heights of the two types of thin-walled structures, the yield strength is higher but the elongation is lower at the bottom position of sample, while the yield strength is lower but the elongation is higher at the middle and top positions. The differences of mechanical properties at different heights of the T1 and T2 samples are related to the microstructure and relative density. This finding provides new insights for the design and performance analysis of complex thin-walled structures formed by additive manufacturing.

Effect of powder properties, process parameters, and recoating speed on powder layer properties measured by in-situ laser profilometry and part properties in laser powder bed fusion

In laser-based powder bed fusion of metals (PBF-LB/M), the powder layer is the link between the powder properties and the resulting part quality. Powder layer quality is a key metric related to powder spreadability and ultimately part quality, yet it is still unclear how it can be quantified. This is due to the difficulty of studying powder layer properties during the process. This study investigates the influence of powder properties, process parameters, and recoating speed on the surface roughness of the powder layer and the part, as well as on the effective thickness of the powder layer and solidified layer, and the resulting relative part density. Utilizing in-situ laser profilometry, high-resolution topographical data of the powder layer and the part surface were acquired, with minimal interference to the PBF-LB/M process. Six AlSi10Mg powders with varying particle size distribution, morphology, and flowability were processed using a wide range of recoating speeds and scan speeds to create powder layers with a wide range of properties. The results reveal a strong correlation between energy input and the effective powder layer thickness where lower scan speed results in an increased effective powder layer thickness due to material losses. Additionally, faster recoating decreases the powder layer density, which is moderated by the median particle size where the effect is strongest for fine powders. The surface roughness of the powder layer and top part surface are influenced by the recoating speed, energy input, and particle size, and they are strongly linked to each other. This highlights the importance of considering realistic substrate surface roughnesses in both powder spreading experiments and simulations. Finally, layer properties affect the process stability, resulting in small differences in relative part density.

High-Fidelity Simulation of the Light-to-Dense Stratification Transient in the HiRJET Facility

Density stratification in a large enclosure is a crucial phenomenon to heat transfer and sustainable passive heat removal of a sodium fast reactor during reactivity transients. However, engineering turbulence models were identified to have unsatisfactory performance in predicting propagation of a stratified front. Yet, the scarcity of high-resolution data for stratification hampers the development of models. To explor e applications of leveraging direct numerical simulation (DNS) data to support turbulence model development, this work conducted DNS using NekRS to study a long stratification transient in the High-Resolution Jet (HiRJET) experimental facility. This work considers an experiment run where light fluid is injected into a tank containing a denser fluid with a relative density difference of 1.5%. Formation of the stratified layer is identified as impingement of the buoyant jet promoting mixing of the two fluids. Based on the transient statistics, transport of the concentration can be characterized by regions with dominating effects of turbulent mixing, buoyant dissipation, and molecular diffusion, respectively, as moving away from the elevation of jet impingement. Concentration near the stratified front also exhibits oscillation at Brunt-Väisälä frequency. Preliminary validation of the simulation showed encouraging agreement of the concentration distribution with the reference experiment.

Investigation of the Mechanical Strength of Artificial Metallic Mandibles with Lattice Structure for Mandibular Reconstruction.

Mandibular reconstructive surgery is necessary for large bone defects. Although various reconstruction methods have been performed clinically, there is no mandibular reconstruction method that meets both sufficient strength criteria and the patient's specific morphology. In this study, the material strength of the cylindrical lattice structures formed by electron-beam melting additive manufacturing using titanium alloy powder was investigated for mandibular reconstruction. The virtual strengths of 28 lattice structures were compared using numerical material tests with finite element method software. Subsequently, to compare the material properties of the selected structures from the preliminary tests, compression test, static bending test and fatigue test were conducted. The results showed that there were correlations with relative density and significant differences among the various structures when comparing internal stress with deformation, although there was a possibility of localized stress concentration and non-uniform stress distribution based on the lattice structure characteristics. These results suggest that the lattice structure of body diagonals with nodes and a cell size of 3.0 mm is a potential candidate for metallic artificial mandibles in mandibular reconstruction surgery.

Modeling of Metal Powder Densification under Hot Isostatic Pressing.

The consolidation of metal powders is a complex thermomechanical process, and the temperature has a significant effect on the density distribution in the compact. The consolidation process of metal powders with an average particle size of 10 μm, 25 μm, and 50 μm under hot isostatic pressure was simulated by finite element modeling. The distribution and evolution of the relative density after being hot isostatic pressing (HIP) under 1050 °C/130 MPa/4 h, 1150 °C/130 MPa/4 h, and 1250 °C/130 MPa/4 h conditions were simulated, respectively. The experimental data of HIP at 1050 °C/130 MPa/4 h were used to verify the modeling results via the geometric change in the container. The relative density difference between the simulated results and the experimental results at different positions was less than 2%. This methodology called "modeling prediction, experimental validation" can accelerate experimental discovery in an economic manner.

Halyomorpha halys (Hemiptera: Pentatomidae) trap captures at orchard and nonorchard sites and the influence of uncultivated woody host plants in adjoining woodlots.

The invasive Halyomorpha halys (Hemiptera: Pentatomidae) has threatened Mid-Atlantic tree fruit since 2010. To identify factors underlying observed differences in H. halys pest pressure among individual orchards within a geographically proximate area, a 3-yr study was conducted across 10 apple orchard and 8 nonorchard sites bordered by unmanaged woodlots. At each site, 3 pheromone traps were monitored weekly for H. halys captures from late April to mid-October. Apple injury was assessed at harvest at orchard sites annually, and a survey of woody plants found in woodlots adjacent to all sites was conducted. There were no significant differences in captures between orchard and nonorchard site types, but captures were significantly different among individual orchard sites and among individual nonorchard sites. A significant positive relationship between the amount of stink bug injury on apple at harvest and late season captures was detected at orchard sites in 2018 and 2019. Among woodlots adjacent to all sites, a significant positive relationship between the proportion of Lonicera spp. and mid- and late-season nymphal captures was identified. Season-long nymphal captures were positively related to the proportion of Lonicera and Elaeagnus and negatively with Sassafras. For adults, captures were negatively related to the proportion of Ailanthus and positively related to the proportion of Fraxinus in the early and mid-season, respectively. Our results indicate that orchard presence was not driving the relative abundance of localized H. halys populations and that differences in relative densities among sites point to other factors, such as abundance of specific uncultivated woody hosts in unmanaged areas.

Mechanics of re-entrant anti-trichiral honeycombs with nature-inspired gradient distributions

This study focuses on the nature-inspired gradient-based approach to re-designing re-entrant anti-trichiral (REAT) honeycombs through extensive experimental quasi-static compression. Novel perspectives on REAT honeycomb are offered through the introduction of gradient distributions on two critical geometrical parameters, the cylindrical diameter (chiral) and height of the unit cell, rather than the traditional thickness-based gradient approach. Chiral-based gradient approach demonstrated clear advantages in elastic stiffness, specific energy absorption (SEA) and densification strain over uniform REAT structures of constant geometrical parameters. These advantages are exhibited in their extended and constantly increasing quasi-plateau stage, consistent specific energy absorption (SEA) especially during early stages of compression, and most importantly, the ability to maintain a relatively constant energy absorption efficiency that is 25% more than that of the Base uniform REAT structure. Height gradient-based REAT structures, on the other hand, were able to leverage on associations between the negative Poisson's ratio (NPR) effect and height of unit cell to demonstrate notable deformation patterns across various portions of the structure. The present work reveals the performance enhancements through alternative gradient-based approaches over thickness-based gradient approaches and highlighted the differences in NPR between layers as the main driver of compressive collapse apart from the commonly concluded difference in relative density.

Traveling internal waves in a two-layer shallow medium with variable bathymetry and current: Surface and near-bottom flows

In the linear approximation, we examine the one-dimensional problem of long internal wave propagation without reflection in a stationary two-layer flow with a free boundary in a channel of variable depth and width, in the limiting cases of surface and near-bottom currents. We use the shallow-water approximation and assume that liquids in the layers are ideal, immiscible, and having a small relative density difference, and that the flow is only in one of the layers. To filter fast processes (such as surface gravity waves), the flow velocity is assumed to have the same order of magnitude as the speed of internal waves. Both surface and near-bottom flows are divided into three classes, in accordance with conditions providing wave propagation without reflection. The properties of the flows in each of the classes are examined, and it is shown that the global reflectionless near-bottom flows do exist. The main results and conclusions are illustrated by a few particular solutions. A detailed comparison with the first part of the study concerning the flows with currents in both layers made it possible to clarify and refine some of the results obtained there, and to formulate questions for further investigation. The results obtained may be of interest for understanding of those natural processes in surface and near-bottom flows, which are significantly influenced by internal waves.

Study on the Hemispheric Asymmetry of Thermospheric Density Based on In-Situ Measurements from APOD Satellite

In this article, high spatiotemporal resolution data obtained by the atmospheric density detector carried by China’s APOD satellite are used to study the hemispheric asymmetry of thermospheric density. A detailed analysis is first performed on the dual magnetic storm event that occurred near the autumnal equinox on 8 September 2017. The results show that the enhancement ratio of atmospheric density in the southern polar region (SPR) on the duskside was approximately 1.33–1.65 times that of the northern polar region (NPR), demonstrating a strong hemispheric asymmetry of thermospheric atmospheric density response during the magnetic storm. However, the asymmetry response was smaller on the dawnside, suggesting that the hemispheric density response asymmetry is related to local time (LT). The energy injection in high-latitude regions increases local atmospheric density and forms traveling atmospheric disturbances (TADs). TADs can propagate to low-latitude regions over several hours and affect the global distribution of thermospheric atmospheric density. Similarly, the geomagnetic index fitting slope of SPR relative density difference is greater than that of NPR. The SuperDARN convection pattern indicates that the plasma convection velocity of SPR is significantly greater than that of NPR, indicating that joule heating caused by neutral friction of ions in the Southern Hemisphere may be stronger. Subsequently, an analysis of annual solar activity and seasons was carried out on the thermospheric NPR, SPR atmospheric density, and their differences from December 2015 to December 2020. The results show that thermospheric atmospheric density decreases overall as the number of sunspots decreases. The differences between the NPR and SPR atmospheric densities in the thermosphere exhibits a noticeable annual periodicity. The NPR and SPR atmospheric densities appear to have different distribution characteristics in different seasons. The NPR density peak is mainly in March or April. In particular, the “double-peak” phenomenon occurred in 2017, with peaks in March and September, while the most obvious feature of SPR atmospheric density is that its minimum value occurs in the summer months of June and July. This paper reveals the annual, seasonal, and magnetic storm response characteristics of the hemispheric asymmetry of thermospheric atmospheric density, which has significant implications for the study of multilayer energy coupling of the magnetosphere–ionosphere–thermosphere.

Traveling internal waves in a two-layer shallow medium with variable bathymetry and current

In the linear approximation, we examine one-dimensional problems of long internal wave propagation in a stationary flow of two-layer fluids with free boundary in a channel of variable depth and width. We use the shallow-water approximation and assume that liquids in the layers are ideal, immiscible, and have a small relative density difference inherent to natural currents. The conditions the flow must satisfy for wave propagation without reflection are found and analyzed. It is shown that there are three classes of such flows, and the characteristic properties of each of them are studied and compared with those found earlier in a similar problem for surface waves. A general analysis of the problem is illustrated by a few particular solutions. The results obtained can be of interest for understanding natural phenomena in which internal waves play a significant role.

Seismic response of a shield tunnel crossing saturated sand deposits with different relative densities

This study investigated the seismic response of a shield tunnel passing saturated sand deposits with different relative densities. The Dafalias and Manzari model was adopted to capture the cyclic behaviour of liquefiable soil subjected to earthquake excitation. A refined lining model was proposed to simulate the mechanical behaviour of segment joints. A fully fluid-solid coupled analysis was then performed to investigate the seismic response of shield tunnels crossing through adjacent sand deposits with different relative densities. The displacement of segment joints and internal force of lining concrete were found to be prominent near the interface. The structure deformation mode consists of the opening, dislocation, and distortion of ring joints. The complicated tunnel deformation mechanism was then clarified. Comprehensive parametric studies were performed to establish some quantitative relationships between the joint displacement and internal force of segmental linings and the normalized parameters. Apart from soil-deposit interface inclination and cover to diameter ratio, the earthquake magnitude and difference in relative densities had a remarkable impact on the seismic response of the tunnel structure near the interface.

Multidimensional grid-based clustering with local differential privacy

Privacy-preserving clustering has received increasing research attention in recent years. Local differential privacy (LDP) is a privacy model without relying on trusted third parties. It plays a crucial role in distributed privacy-preserving clustering. Most previous methods focus on partition-based clustering (e.g., k-means), which necessitates many iterative interactions. Massive iterations cause a division of the privacy budget and increase the amount of individual noise, affecting the clustering utility. To address this issue, we turn to grid-based clustering and design the GC-LDP algorithm to balance the privacy and clustering utility with only three rounds of interactions. In GC-LDP, our core contribution is to develop a non-uniform grid division method via the coefficient of variation (CV), which can generate a grid structure approximating the global data distribution within two rounds of interactions. Besides, we designed a new perturbation mechanism to reduce the amount of individual noise injection. Further, a cell aggregation method is developed by exploring the relative density difference among grids to achieve multi-density clustering. Theoretical analysis and experiments on real-world datasets show that GC-LDP can obtain high-quality clustering results while satisfying local differential privacy.

In-situ monitoring of powder bed fusion of metals using eddy current testing

Powder bed fusion of metals (PBF-LB/M) is the most commonly used additive manufacturing process for the layerwise production of metal parts. Although the technology has developed rapidly in recent years, manufactured parts still lack consistent quality primarily owing to process-inherent variability, and the lack of effective sensing technologies enabling the ability to control the process during part production. Thus, there are high costs caused by rigorous post-process part inspection steps required to provide compliant part certificates. In contrast to typically deployed in-situ sensing technologies, eddy current testing (ECT) is a standardized nondestructive testing (NDT) technique able to provide compliant part certificates during post-process inspection according to existing standards. This study investigates the potential of ECT as an in-situ process monitoring technology for PBF-LB/M. Parts made from AlSi10Mg were manufactured on a PBF-LB/M machine using different process parameters yielding different relative densities ranging from 99%– 99.7%. During the build cycle, the parts were measured layer-by-layer with an ECT system mounted on the machine recoater. Signal analysis methods were developed which effectively separate and calibrate the electrical conductivity component (relative electrical conductivity) and the distance component (lift-off) of the ECT signals. The relative electrical conductivity was then compared to X-ray micro-computed tomography ( μ CT) measurement data demonstrating that layer-to-layer differences in relative density of about 0.1% can be successfully detected via ECT. In addition, the lift-off was used to monitor the thickness of the consolidated layers and the layer-to-layer part height. The results show that ECT is an effective technology for in-situ monitoring of the relative part density paving the way for deploying ECT for in-situ NDT of PBF-LB/M-manufactured parts.

A comprehensive study on physicochemical properties, bioactive compounds, and emulsified lipid digestion characteristics of Idesia polycarpa var. Vestita Diels fruits oil

Idesia polycarpa var. vestita Diels fruits oil (IPO) has the potential to broaden the availability of healthy vegetable oil and relieve pressure on the edible oil supply. In this study, we compared the physicochemical, bioactivity, and digestive properties of IPO, olive oil (OO), and soybean oil (SO) to comprehensively evaluate the edible potential of IPO. The results revealed no significant differences in relative density or refractive index among the three oils. IPO was rich in β-sitosterol (366.74 mg/100 g), β-tocopherol (8.42 mg/100 g), and α-tocopherol (37.10 mg/100 g). The digestive properties of IPO emulsion were investigated for the first time using in vitro simulated digestion. The IPO emulsion stood out regarding its free fatty acid release (88.03 %). Finally, the IPO emulsion released mainly unsaturated fatty acids and had a higher monoacylglycerol content. This study provides new insights into IPO as a high-quality edible vegetable oil.

Pengaruh Tinggi Muka Air Terhadap Deformasi Tanah Terlikuefaksi

Liquefaction occurs in saturated loose sandy soils that experience an increase in pore water pressure due to the propagation of earthquake waves to the ground surface. This phenomenon raises various questions such as how the groundwater level can affect the occurrence of liquefaction events at different earthquake strengths. The purpose of this study was to determine the effect of groundwater level on liquefaction-prone soils at different seismic peak acceleration values and the effect of relative density (Dr) values on liquefaction-prone soils with variations in groundwater level and earthquake acceleration. In this study, a sample of Jono Oge sand soil was used from the occurrence of liquefaction that met the gradation criteria. The soil was separated through the #8 sieve and retained #100. The modeling technique is carried out with several variables such as the ratio of groundwater level (Hw/Hs) of 25%, 50%, 75%, and 90%, relative density (Dr) 30%-40% and 40%-50%, and at different peak accelerations of 0.3g and 0.4g. The modeling test uses a sieve shaker for earthquake vibrations.. The results of the study show that the difference in groundwater level affects the subsidence of liquefied soil where the settlement will be accure greater in the ratio of the groundwater level (Hw/Hs) and the peak acceleration is greater and vice versa, the difference in relative density (Dr) also affects the magnitude of the the settlement where the lower the Dr value for Hw/Hs and the greater the peak acceleration, the greater the settlement will be occure.

Characterization and Analysis of the Thermal Conductivity of AlSi10Mg Fabricated by Laser Powder Bed Fusion

Abstract Laser-based powder bed fusion (L-PBF) of AlSi10Mg can be used to fabricate complex, light-weight structures with high thermal conductivity. Much effort has gone into investigating the mechanical behavior of L-PBF components; however, few studies investigated their thermal properties. This investigation characterizes the effect of process parameters on the relative density and thermal conductivity of L-PBF AlSi10Mg. Exposure time, laser power, pointwise distance, and build orientation were examined. Results show that changing these parameters can affect the thermal conductivity by up to 22%. For example, build orientation and pointwise distance influenced the thermal conductivity by 12.9% and 10%, respectively. As the pointwise distance increased, both the conductivity and the distance between the melt pool boundaries decreased, whereas the laser power had a negligible effect on both. The effect of exposure time was mainly dependent on the pointwise distance. It is shown that thermal conductivity is not only related to the relative density of the samples, but the number of the melt pool boundaries in the microstructure also plays a significant role in interrupting the heat flow. A new factor is introduced to account for the number of melt pool boundaries per unit length in the direction of heat flow, which helps to explain the variation in thermal conductivity for samples manufactured with high energy densities which had almost negligible difference in relative density.

Physical and Mechanical Properties of Stems and Branches of Falcata [Falcataria moluccana (Miq.) Barneby & J.W. Grimes] Grown in Caraga, Philippines

The physical and mechanical properties of branch wood from falcata [Falcataria molucanna (Miq.) Barneby & J.W. Grimes] grown in Caraga Region, Philippines were determined to assess suitability for end-uses such as core veneer and as material for light construction and handles and boxes as the stem wood. Tests done to compare the properties with the stem wood showed significant differences in relative density (average values of 0.284 for the stem wood and 0.255 for the branch wood) and shrinkage properties in all directions. Axial position significantly influenced variation in moisture content (p = 0.0024) for stem and branch wood, as well as relative density (p = < 0.0001) plus percent tangential (p = < 0.0001) and radial (p = 0.0014) shrinkage. For the mechanical properties, the stem wood end hardness was significantly higher by 28.8% at green condition (p = 0.0003) and by 13.36% at 12% MC (p = 0.0133) than the branch wood. The compression perpendicular to the grain at 12% MC of the stem wood was also higher by 16.10% (p = 0.0166). However, for the other mechanical properties studied, the differences were not significant. The bottom portion of the stem and branch wood exhibited the highest mechanical properties, which can be attributed to the higher relative density at this portion (p = 0.0001). Based on the results that showed insignificant differences in most of the properties between the wood types of F. moluccana, the branch wood can possibly be used for similar applications as the stem wood such as for light construction, non-structural veneer, and plywood; for tool handles, boxes, and other household items; and for pulp and paper. The utilization of the branch wood of F. moluccana, therefore, can augment the raw materials supply for the local wood industry.