Towards better predicting the settling velocity of film-shaped microplastics based on experiment and simulation data

The properties of microplastics determine their settling velocities and affect the fates and migration pathways of microplastics. This paper has simulated the settling velocities of film-shaped microplastics, which are present in natural aquatic environments. The numerical results provided more data to fit the terminal settling velocities of film-shaped microplastics. Comparison between the particle definition and the equivalent spherical diameter confirmed that the particle definition is more suitable for film-shaped microplastics. In the transitional flow regime, CD decreases linearly with Re. As Re further increases, CD gradually converges at approximately 1.20. By integrating the experimental and simulated data, a new explicit formula for predicting the settling velocity of film-shaped microplastics has been presented with the optimal shape parameter f. The presented formula achieves better performance (MAPE = 6.6 %, RMSE = 16.8 %, and R2 = 0.99) than the existing formulas for settling velocity for film-shaped microplastics, closely rivaling that of the ensemble learning algorithm.

A modified drag coefficient model for calculating the terminal settling velocity and horizontal diffusion distance of irregular plume particles in deep-sea mining

Deep-sea mining inevitably produces plumes, which will pose a serious threat to the marine environment with the continuous movement and diffusion of plumes along with ocean currents. The terminal settling velocity (wt) of irregular particles is one of the crucial factors for determining the plumes' diffusion range. It is generally calculated by drag coefficient (CD), while most existing CD models only consider single shape characteristic parameter or have a smaller range of Reynolds number (Re). In this study, a new shape factor (γ) of irregular particles is proposed by considering the thickness (one-dimension), the projected area (two-dimension), and the surface area (three-dimension) of irregular particles as well as their coupling effect to establish a modified CD model for calculating the wt. A modified Gaussian plume model is proposed to predict the horizontal diffusion distance of the plume particles by considering the settling velocity and diffusion effect of irregular particles. Research results show that the wt increases nearly linearly, with a gradually decreased slope and slightly then greatly with the increasing of γ, dp (diameter) and ρp (density), respectively. The modified CD model is verified to be more valid with a wider application range (Re < 3×105) than five existing CD models by the test results. The larger the ρp or dp, the larger the wt and thus the smaller the Sh. This study could provide a theoretical basis for calculating the plume diffusion range to further study the impact of deep-sea mining on the ocean environment.

Settling velocity of submillimeter microplastic fibers in still water

Microplastic fibers (MPFs) are one of the most important MP contaminants of aquatic environments. However, little research has been conducted on the movement of submillimeter MPFs in water. Herein, the settling of 519 submillimeter MPFs in still water was measured and the settling velocity was analyzed. Observations of the settling velocity of MPFs with lengths of 300, 500, and 600 μm showed that most MPFs settled individually or in pairs. The sedimentation of a single fiber could be divided into three patterns, that is, horizontal, inclined, and vertical. The average settling velocity increased with an increase in the MPFs length and orientation angle. As the MPFs length increased, the probability of inclined settlement decreased but that of horizontal settlement increased. The horizontal velocity of single fibers also was investigated, and the horizontal and vertical settling of MPFs exhibited minimal horizontal velocity. Because of the considerable difference between the calculated drag coefficients from existing drag coefficient models and experimental values, a drag coefficient model was developed with a deviation of <3 %. Four settling patterns were identified for two fibers, that is, X shaped, inverted-T shaped, cross shaped, and overlapping. The average velocity of the overlapping settlement of two fibers was considerably higher than that of the other three settling patterns. The average settling velocity of 600-μm two fibers was 1.47 times that of single fibers, indicating that their corresponding drag coefficient was ~46 % that of a single fiber.

E-cadherin adhesion dynamics as revealed by an accelerated force ramp are dependent upon the presence of α-catenin

Tissue remodeling and shape changes often rely on force-induced cell rearrangements occurring via cell-cell contact dynamics. Epithelial cell-cell contact shape changes are particularly dependent upon E-cadherin adhesion dynamics which are directly influenced by cell-generated and external forces. While both the mobility of E-cadherin adhesions and their adhesion strength have been reported before, it is not clear how these two aspects of E-cadherin adhesion dynamics are related. Here, using magnetic pulling cytometry, we applied an accelerated force ramp on the E-cadherin adhesion between an E-cadherin-coated magnetic microbead and an epithelial cell to ascertain this relationship. Our approach enables the determination of the adhesion strength and force-dependent mobility of individual adhesions, which revealed a direct correlation between these key characteristics. Since α-catenin has previously been reported to play a role in both E-cadherin mobility and adhesion strength when studied independently, we also probed epithelial cells in which α-catenin has been knocked out. We found that, in the absence of α-catenin, E-cadherin adhesions not only had lower adhesion strength, as expected, but were also more mobile. We observed that α-catenin was required for the recovery of strained cell-cell contacts and propose that the adhesion strength and force-dependent mobility of E-cadherin adhesions act in tandem to regulate cell-cell contact homeostasis. Our approach introduces a method which relates the force-dependent adhesion mobility to adhesion strength and highlights the morphological role played by α-catenin in E-cadherin adhesion dynamics.

A new model for the terminal settling velocity of microplastics

Microplastic (MP) settling process is important for the transport of microplastic particles (MPs, <5 mm) in water bodies. However, for the control parameter of the drag coefficient (C_d), no generalized formula has been proposed for MPs of different shapes and materials. In this study, a total of 1343 MP settling data were collected from the literature. It was found that the drag law for perfect spheres cannot reasonably predict C_d for MPs with particle Reynolds number of 1-10³. A new formula for C_d was developed by introducing the dimensionless particle diameter (d_⁎) and two shape descriptors. The absolute error of the new formula is 15.2%, smaller than those (42.5-72.8%) of other existing formulas. Moreover, an explicit model was developed for MP settling velocity by correlating C_d, d_⁎, and shape descriptors, with lower absolute error (8.8%) than those (15.4-77.2%) of existing models.

A new model for settling velocity of non-spherical particles

The settlement of non-spherical particles, such as propagules of plants and natural sediments, is commonly observed in riverine ecosystems. The settling process is influenced by both particle properties (size, density, and shape) and fluid properties (density and viscosity). Therefore, the drag law of non-spherical particles is a function of both particle Reynolds number and particle shape. Herein, a total of 828 settling data are collected from the literatures, which cover a wide range of particle Reynolds number (0.008-10000). To characterize the influence of particle shapes, sphericity is adopted as the general shape factor, which varies from 0.421 to 1.0. By comparing the measured drag with the standard drag curve of spheres, we modify the spherical drag law with three shape-dependent functions to develop a new drag law for non-spherical particles. Combined with an iterative procedure, a new model is thus obtained to predict the settling velocity of non-spherical particles of various shapes and materials. Further applications in hydrochorous propagule dispersal and sediment transport are projected based on deeper understanding of the settling process.

Inhalation and deposition of spherical and pollen particles after middle turbinate resection in a human nasal cavity

Middle turbinate resection significantly alters the anatomy and redistributes the inhaled air. The superior half of the main nasal cavity is opened up, increasing accessibility to the region. This is expected to increase inhalation dosimetry to the region during exposure to airborne particles. This study investigated the influence of middle turbinate resection on the deposition of inhaled pollutants that cover spherical and non-spherical particles (e.g. pollen). A computational model of the nasal cavity from CT scans, and its corresponding post-operative model with virtual surgery performed was created. Two constant flow rates of 5 L/min, and 15 L/min were simulated under a laminar flow field. Inhaled particles including pollen (non-spherical), and a spherical particle with reference density of 1000 kg/m³ were introduced in the surrounding atmosphere. The effect of surgery was most prominent in the less patent cavity side, since the change in anatomy was proportionally greater relative to the original airway space. The left cavity produced an increase in particle deposition at a flow rate of 15 L/min. The main particle deposition mechanisms were inertial impaction, and to a lesser degree gravitational sedimentation. The results are expected to provide insight into inhalation efficiency of different aerosol types, and the likelihood of deposition in different nasal cavity surfaces.

Analysis of why sea turtles swim slowly: a metabolic and mechanical approach

Animals with high resting metabolic rates and low drag coefficients typically have fast optimal swim speeds in order to minimise energy costs per unit travel distance. The cruising swim speeds of sea turtles (0.5-0.6 m s^-1) are slower than those of seabirds and marine mammals (1-2 m s^-1). This study measured the resting metabolic rates and drag coefficients of sea turtles to answer two questions: (1) do turtles swim at the optimal swim speed?; and (2) what factors control the optimal swim speed of turtles? The resting metabolic rates of 13 loggerhead and 12 green turtles were measured; then, the cruising swim speeds of 15 loggerhead and 9 green turtles were measured and their drag coefficients were estimated under natural conditions. The measured cruising swim speeds (0.27-0.50 m s^-1) agreed with predicted optimal swim speeds (0.19-0.32 m s^-1). The resting metabolic rates of turtles were approximately one-twentieth those of penguins, and the products of the drag coefficient and frontal area of turtles were 8.6 times higher than those of penguins. Therefore, our results suggest that both low resting metabolic rate and high drag coefficient of turtles determine their slow cruising speed.

Synthesising wave attenuation for seagrass: Drag coefficient as a unifying indicator

An estimated 100 million people inhabit coastal areas at risk from flooding and erosion due to climate change. Seagrass meadows, like other coastal ecosystems, attenuate waves. Due to inconsistencies in how wave attenuation is measured results cannot be directly compared. We synthesised data from laboratory and field experiments of seagrass-wave attenuation by converting measurements to drag coefficients (C_D). Drag coefficients varied from 0.02-5.12 with C_D¯ = 0.74 for studies conducted in turbulent flow in non-storm conditions. A statistical model suggested that seagrass species affects C_D although the exact mechanism remains unclear. A wave model using the estimated C_D¯ as an input parameter demonstrated that wave attenuation increased with meadow length, shoot density, shoot width and canopy height. Findings can be used to estimate wave attenuation by seagrass, in any given set of conditions.

Field-measured drag area is a key correlate of level cycling time trial performance

Drag area (Ad ) is a primary factor determining aerodynamic resistance during level cycling and is therefore a key determinant of level time trial performance. However, Ad has traditionally been difficult to measure. Our purpose was to determine the value of adding field-measured Ad as a correlate of level cycling time trial performance. In the field, 19 male cyclists performed a level (22.1 km) time trial. Separately, field-determined Ad and rolling resistance were calculated for subjects along with projected frontal area assessed directly (AP ) and indirectly (Est AP ). Also, a graded exercise test was performed to determine [Formula: see text] peak, lactate threshold (LT), and economy. [Formula: see text] peak ([Formula: see text]) and power at LT were significantly correlated to power measured during the time trial (r = 0.83 and 0.69, respectively) but were not significantly correlated to performance time (r = - 0.42 and -0.45). The correlation with performance time improved significantly (p < 0.05) when these variables were normalized to Ad . Of note, Ad alone was better correlated to performance time (r = 0.85, p < 0.001) than any combination of non-normalized physiological measure. The best correlate with performance time was field-measured power output during the time trial normalized to Ad (r = - 0.92). AP only accounted for 54% of the variability in Ad . Accordingly, the correlation to performance time was significantly lower using power normalized to AP (r = - 0.75) or Est AP (r = - 0.71). In conclusion, unless normalized to Ad , level time trial performance in the field was not highly correlated to common laboratory measures. Furthermore, our field-measured Ad is easy to determine and was the single best predictor of level time trial performance.

Flux measurements in the surface Marine Atmospheric Boundary Layer over the Aegean Sea, Greece

Micro-meteorological measurements within the surface Marine Atmospheric Boundary Layer took place at the shoreline of two islands at northern and south-eastern Aegean Sea of Greece. The primary goal of these experimental campaigns was to study the momentum, heat and humidity fluxes over this part of the north-eastern Mediterranean Sea, characterized by limited spatial and temporal scales which could affect these exchanges at the air-sea interface. The great majority of the obtained records from both sites gave higher values up to factor of two, compared with the estimations from the most widely used parametric formulas that came mostly from measurements over open seas and oceans. Friction velocity values from both campaigns varied within the same range and presented strong correlation with the wind speed at 10 m height while the calculated drag coefficient values at the same height for both sites were found to be constant in relation with the wind speed. Using eddy correlation analysis, the heat flux values were calculated (virtual heat fluxes varied from -60 to 40 W/m(2)) and it was found that they are affected by the limited spatial and temporal scales of the responding air-sea interaction mechanism. Similarly, the humidity fluxes appeared to be strongly influenced by the observed intense spatial heterogeneity of the sea surface temperature.