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The aim of this study is to determine the misconceptions of Greek junior high school students regarding the floating and sinking of a body through the concept of density. Density is included in most international curricula for this age group and is revisited in Greek junior high schools after being introduced in primary school. After interviews with teachers who teach the physics course, in order to discover the students' way of thinking and their common misconceptions, the researchers of this study created targeted questionnaires for students aged 11-12 years old. During the 2022-23 school year, the questionnaires were handed out to 47 first-grade students at a junior high school in Athens, Greece. Before being administered to the students, the questionnaires were subjected to a content validity test by five physics experts according to Aiken's V index. Then, they were completed by the students before the lesson was taught. After the students had completed the initial questionnaire, a teaching proposal focused on the density-based approach was presented to them. Subsequently, the students filled out the same questionnaire again following the instructional session. Statistical analysis demonstrated a notable enhancement in the comprehension of the misconceptions addressed in this study, with the rates of improvement varying between 18.08% and 52.13%. Consequently, the instructional proposal proved to be instrumental in advancing students' conceptual understanding of floating and sinking within the framework of density interpretation. [ABSTRACT FROM AUTHOR]

Kelps are resilient organisms, capable of thriving in high-energy wave environments. However, when hydrodynamic drag forces exerted by the wave environment exceed the kelps' structural limits, individuals become dislodged. Floating kelps generally follow ocean currents, traveling long distances until air-filled structures fail or the epibiont load becomes too great, causing them to sink to the seafloor. The ability of kelp to disperse over vast offshore and nearshore systems makes them important for organic subsidy and as a dispersal vector for marine organisms. Previous research on dislodged macroalgae focused on context-specific rafts, limiting insights into the broader ecological role of floating kelp. This study employed a site-specific Lagrangian trajectory model to describe the spatial distribution of floating Ecklonia maxima along the South African coastline. The model incorporated buoyancy and sinking using site-specific morphological data. Findings revealed that the distribution of floating E. maxima is influenced by oceanographic conditions, and seasonal patterns were also evident. Mesoscale features played a vital role in kelp accumulation on the surface and seafloor and acted as barriers to dispersal. This study offers essential insights into kelp's role as an organic subsidy and provides numerical evidence for kelp's potential as a carbon sink, contributing to a better understanding of kelp ecosystems and their ecological functions. [ABSTRACT FROM AUTHOR]

Sinking accidents can cause catastrophic losses in human, economic resources and environmental damage. Sinking accidents are one of the most common maritime accidents that occur in Indonesia. Therefore, this study aims to analyze the cause-and-effect probability of ship sinkings in Indonesian waters. Bayesian Network method and accident factor level are used to analyze the causal factors of ship sinking accidents. The results found that the Loss of Stability of the vessel is the most sensitive node. An additional take from the investigated sinking is that half of the accidents occurred on passenger vessels, and ships over 25 years old are prone to sinking due to corrosion and lack of proper maintenance. While 70.5% of accident caused by human error that is majorly triggered by unsafe acts. The real-case analysis also performed in this study reveals that eliminating Human Error and ship’s associated factors can reduce the probability of sinking by 17.2%. [ABSTRACT FROM AUTHOR]

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Sinking of microplastics (MPs) after biofouling is considered an important mechanisms responsible for the downward transport/sedimentation of MPs in the ocean and freshwaters. Previous studies demonstrated MP sinking caused by an increase in the composite density of MPs after biofouling, while MPs with smaller size or shapes with higher surface area to volume ratios (SA:V), such as films, are speculated to sink faster. In this study, we designed an in situ microcosm to simulate the ambient environmental conditions experienced by floating MPs to elucidate the biofouling and sinking of polyethylene (PE), polypropylene (PP), and expanded-polystyrene (EPS) MPs of various sizes and shapes. Our results showed smaller PE and PP MP granules sank faster than large ones. Even EPS granules of 100 μm diameter, having a much lower density (0.02 mg/mm3) than water, started to sink after 2 weeks of biofouling. Moreover, PE film and fiber MPs with higher SA:V did not sink faster than PE MP granules of the same mass, implying that mechanisms other than SA:V, such as fouling contact area and drag coefficient, play a role in the regulation of biofouling and sinking of MPs.

The sinking of outfall pipeline is the key link in the process of shipping and installing marine outfall pipelines. A steel pipeline with a length of 500 m and an inner diameter of 1 m is taken as the research object. The critical depth of pipe sinking is determined by numerical analysis and the equivalent stress of S-shaped pipe section is taken as the limiting condition. The buoyancy, number and spacing of the airbag are determined by the buoyancy aid safety factor and negative buoyancy of the pipe section. The sinking of the outfall pipeline is finally realized by means of multiple underwater sinking. The elevation error, axial error and flange joint gap in the engineering example all meet the acceptance requirements, which proves that the sinking technology is reliable and the application effect is good, and can provide reference for the construction of the same type of outfall pipelines. [ABSTRACT FROM AUTHOR]

Phytoplankton sinking is a major component of vertical ocean carbon and nutrient fluxes, and sinking is an integral component of phytoplankton biology and ecology. Much of our understanding of phytoplankton sinking derives from the settling column method (SETCOL) in which sinking speeds are calculated from the proportion of cells reaching the bottom of a water-filled column after a set time. Video-based methods are a recent alternative to SETCOL in which sinking speeds are measured by tracking the movement of individual cells in a salinity-stratified water column. In this study, we present the results of a meta-analysis showing that SETCOL produces significantly and consistently lower sinking speeds than the video method. Next, we perform a particle image velocimetry analysis, which shows that the observed discrepancy in sinking speeds between the two methods can probably be explained by weak convection currents in the SETCOLs. Finally, we discuss the implications of these results for the interpretation of past and future phytoplankton sinking speed measurements and models that rely on those measurements.

Although the Brazilian Amazon is still one of the most well-conserved environments in the world, it contains an extensive network of waterways that are used by a wide range of vessels that transport both people and cargo, as well as undertaking other activities. To plan environmental risk disaster strategies here, the potential effects of technological disasters, including marine accidents, must be taken into consideration. This paper seeks to redress this by providing a review of the possible risks to the Amazon aquatic environment that could result from various types of marine accidents. While the Amazon region has been researched worldwide, both extensively and intensively, regarding land use, climate, and environmental characterization, work in this field is scarce. A review of the main environmental characteristics of the Amazon is provided, including a description of common marine accidents that have occurred in this region. The environmental impacts experienced by the aquatic environment due to marine accidents worldwide were reviewed from the scientific literature to examine potential risks to the Amazon waterways. It was found that marine accidents, such as fire/explosions and the sinking of ships with different types of cargo, can cause the spillage of oil and other hazardous materials, causing catastrophic damage to the aquatic environment. Changes in the hydrological characteristics of rivers, including unexpected changes in the weather, such as heavy rain and winds, may also influence pollutant dispersion. Initiatives to deal with these technological hazards in the Amazon basin should also consider the potential social and environmental impacts in the protected areas of this region. It is hoped that this paper can serve as a starting point toward the governance and planning of risk disaster management actions, which are aimed at reducing the negative environmental impacts caused by marine accidents in the region. [ABSTRACT FROM AUTHOR]

This paper evaluates the susceptibility to subsidence and collapses in karst terrains of Campeche, Mexico, assuming that under a set of conditioning factors these phenomena occur with greater or lesser intensity and may represent a hazard to the population and economic activities. The conceptual model proposes the relative weighting of susceptible areas through multicriteria analysis of analytical hierarchies including lithological, structural, and environmental factors that affect the geomechanics of subsidence and collapse. The conceptual model is translated into a logical one in a Geographic Information System (ArcMap) from which a susceptibility map with four levels is obtained, very high with 13% of the state area, high 25%, medium 30% and low 32%. The susceptibility values correspond to the levels of predisposition of the terrain to hazard. It is concluded that the susceptibility map is a preventive threat cartographic document, useful at the regional level. [ABSTRACT FROM AUTHOR]

In this work, we establish a two-dimensional axisymmetric simulation model to numerically study the impacting behaviors between oil droplets and an immiscible aqueous solution based on the three-phase field method. The numerical model is established by using the commercial software of COMSOL Multiphysics first and then validated by comparing the numerical results with the previous experimental study. The simulation results show that under the impact of oil droplets, a crater will form on the surface of the aqueous solution, which firstly expands and then collapses with the transfer and dissipation of kinetic energy of this three-phase system. As for the droplet, it flattens, spreads, stretches, or immerses on the crater surface and finally achieves an equilibrium state at the gas–liquid interface after experiencing several sinking-bouncing circles. The impacting velocity, fluid density, viscosity, interfacial tension, droplet size, and the property of non-Newtonian fluids all play important roles in the impact between oil droplets and aqueous solution. The conclusions can help to cognize the mechanism of droplet impact on an immiscible fluid and provide useful guidelines for those applications concerning droplet impact. [ABSTRACT FROM AUTHOR]

Diatoms represent the most abundant and diversified class of primary producers in present oceans; their distinctive trait is the ability to incorporate silicic acid in a silica outer shell called frustule. Numerous adaptative functions are ascribed to frustules, including the control of vertical movements through the water column; this indirectly determines cell access to fundamental resources such as light and nutrients, and favors diatom escape from predators. At the same time, light guides phototroph movements in the water column by affecting cell density (e.g., by modulating Si deposition in diatoms, vacuole volume, and/or solution). We investigated how the tremendous diversity in morphology and silicification that characterizes the frustule and the crucial role of light in diatom spatial distribution govern diatom sinking capacity. To test their integrative effects, we acclimated four diatoms distinguished by frustule traits (Chaetoceros muelleri, Conticribra weissflogii, Phaeodactylum tricornutum, and Cylindrotheca fusiformis) to different light conditions and evaluated their physiological performance in terms of growth, elemental composition, morphological changes, and their in vivo sinking capacity. What emerged from this study was that silicification, more than other morphological characteristics, controls species vertical movements, while a higher energy availability enhances cell floating independently from the silica content. [ABSTRACT FROM AUTHOR]

Diatoms represent the most abundant and diversified class of primary producers in present oceans; their distinctive trait is the ability to incorporate silicic acid in a silica outer shell called frustule. Numerous adaptative functions are ascribed to frustules, including the control of vertical movements through the water column; this indirectly determines cell access to fundamental resources such as light and nutrients, and favors diatom escape from predators. At the same time, light guides phototroph movements in the water column by affecting cell density (e.g., by modulating Si deposition in diatoms, vacuole volume, and/or solution). We investigated how the tremendous diversity in morphology and silicification that characterizes the frustule and the crucial role of light in diatom spatial distribution govern diatom sinking capacity. To test their integrative effects, we acclimated four diatoms distinguished by frustule traits (Chaetoceros muelleri, Conticribra weissflogii, Phaeodactylum tricornutum, and Cylindrotheca fusiformis) to different light conditions and evaluated their physiological performance in terms of growth, elemental composition, morphological changes, and their in vivo sinking capacity. What emerged from this study was that silicification, more than other morphological characteristics, controls species vertical movements, while a higher energy availability enhances cell floating independently from the silica content.

Arc machining is suitable for efficiently processing typical difficult-to-cut material Ti6Al4V. Traditional arc sinking machining commonly uses water-based dielectric because of its safety and good cooling capacity. However, water-based dielectric generally has high conductivity that causes frequent short circuits and strong electrolytic reactions during machining, thereby reducing machining stability and deteriorating machining performance. This paper proposes a novel high-efficient compound sinking machining that combines arc machining with electrical discharge machining (EDM). The dielectric is formed by dispersing oxygen into deionized water, thus reducing the shortcomings of traditional water-based dielectric and introducing the advantages of gas-based one. The feasibility of the proposed method is systematically studied compared to the method that uses deionized water. Influences of oxygen pressure, pulse duration, and peak current are investigated. Characteristics of surface topography and recast layer are also studied. Results suggest that the properties of dielectric improve, and the machining stability and machining intensity increase with the assistance of oxygen. Therefore, compared with using deionized water, the proposed method shows better processing characteristics, including larger material removal rate (MRR), smaller relative electrode wear rate (REWR), and thinner recast layers. The proposed method is promising to process Ti6Al4V due to its high efficiency and environment-friendly properties. [ABSTRACT FROM AUTHOR]

The Cheonan, a patrol combat corvette of the South Korean (SK) Navy, sank during a routine patrol mission in the Yellow Sea in March 2010. An SK government report concluded that a North Korean (NK) submarine torpedo attack was responsible for the Cheonan sinking. This report presented a torpedo propulsion section as the conclusive evidence of an NK torpedo attack on the Cheonan. However, a forensic corrosion analysis of this torpedo propulsion section proved it could not have been involved in the Cheonan sinking. Instead, the deformation characteristics of Cheonan's hull plate and main deck are more consistent with damage due to a collision with a submarine than a torpedo explosion. Evidence that led to this conclusion is presented and discussed. [ABSTRACT FROM AUTHOR]

A low-cost methodology is proposed to provide settlement data for solid blocks in order to improve the design of future coastal structures. Two methods were used to determine how far the block was sinking at the sandy bottom: topographically (four field campaigns) and continuously (with two pressure sensors) for 7.5 months. Settlement values obtained were similar in both cases. The difference between both methods at most 2 cm. Half of the sink occurred in the first week. Over the next month, the rate of sinking slowed down until a storm ended it all. Subsequently, the blocks remained stable. A comparison with other researchers' data was performed and significant differences were found. This heterogeneity in behaviour necessitate the use of these types of low-cost tests that would help calibrate both physical and numerical models. • A new affordable way to find out absolute and relative values of concrete block sinking in the sea bottom is shown. • The methodology showed here is a very low cost technique. • Real data of a practical case of great utility for the calibration and validation of physical and mathematical models are also presented. • Amount the results, it is worthy of to highlight that most of the sinking was observed in the first week. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems are viewed as a key medium for the transport of land-based plastics into oceans. Microplastic (MP) particles in freshwater environments demonstrate high persistence and an extensive range of size and shape distributions, which make their mobility, distribution, and fate vary distinctly depending on the prevailing environmental conditions. The inherent physical properties of different plastic polymers are constantly evolving at different specific reaction rates due to the complex weathering processes in the environment. This continuously alters the underlying mechanisms governing MP dynamics and further complicates their ultimate fate in natural aquatic systems. This paper conducts a comprehensive review of the dynamic behaviour of MPs in freshwater ecosystems, focusing on investigating the settling, aggregation, retention, and suspension processes governing their transport from the source to the sink. We provide an in-depth overview of the key theoretical foundations of MP behaviour in ambient flows and the key influential factors (i.e. size, density, shape, composition). Our findings highlight intricate interplays between MP dynamic behaviours and local hydrodynamics and water chemistry, which lead to the continuous evolution of MP physicochemical properties (e.g., size, surface charge) through interactions with suspended solids, organic natural matter, and microorganisms under light and wind exposure. This dynamic poses significant challenges in predicting MP transport processes and ultimate fate. Gap analysis highlights the discrepancy between current models based on controlled laboratory conditions and complex natural environments, signifying the need for investigating MP dynamic behaviour across a wide range of environmental conditions (e.g. simulating complex flow patterns and solution chemistries of real water bodies). Further research is needed to expand field studies to correlate environment hydrodynamics with MP abundance and to conduct mesoscale experiments that accurately reflect the effects of weathering and flow hydrodynamics on MP behaviours. Integrating detailed physical experiments with numerical modelling tools is essential for a comprehensive understanding of the interactions among various MPs and their overall impact on the environment. This facilitates robust and reliable environmental risk assessment for MP control and pollution management. Key dynamic process affecting the fate of microplastics in freshwater systems. [Display omitted] [ABSTRACT FROM AUTHOR]

In this work, we establish a two-dimensional axisymmetric simulation model to numerically study the impacting behaviors between oil droplets and an immiscible aqueous solution based on the three-phase field method. The numerical model is established by using the commercial software of COMSOL Multiphysics first and then validated by comparing the numerical results with the previous experimental study. The simulation results show that under the impact of oil droplets, a crater will form on the surface of the aqueous solution, which firstly expands and then collapses with the transfer and dissipation of kinetic energy of this three-phase system. As for the droplet, it flattens, spreads, stretches, or immerses on the crater surface and finally achieves an equilibrium state at the gas–liquid interface after experiencing several sinking-bouncing circles. The impacting velocity, fluid density, viscosity, interfacial tension, droplet size, and the property of non-Newtonian fluids all play important roles in the impact between oil droplets and aqueous solution. The conclusions can help to cognize the mechanism of droplet impact on an immiscible fluid and provide useful guidelines for those applications concerning droplet impact.

This study aims to explore the pattern of external representation of suspending objects in a static fluid. The study used a qualitative descriptive method involving 57 elementary, junior, senior school, and university students. Data collection implemented a 30-item test covering the dominant context of suspending and partially floating and sinking. Some of phenomenographic steps were adapted in data analysis. Based on the data analysis, it can be concluded that there is a dominant external representation pattern, where there is a simplification of the depiction of suspending objects. Suspending position tends to be locked in a limited area, namely in the middle of the depth of the liquid. In the context of suspending objects' cuts, the cuts were generally represented by an upward shifting pattern. Factors that influence the pattern of representation are the involvement of intuition in conceptualizing the phenomena presented, and the conceptual aspect of density has not been integrated into the reasoning process for compiling external representations, both diagrams, and texts. Research limitation is presented in this article. [ABSTRACT FROM AUTHOR]

This study aims to explore the mental models of students about suspending objects in liquid fluid. The study used a descriptive qualitative method and implemented crosssectional approach. It involved 57 students from grade 5 of elementary school to fourthyear prospective physics teachers. The data collection used a test consisting of twenty-six essay and four multiple-choice items, which covered several contexts and factors. The data were analyzed by adapted phenomenographic procedures and integrated with some stages of thematic analysis. The types of mental models that were successfully explored include the density-, mass-, weight-, volume-, and gravity-based model, leaked boat model, air as a floater model, etc. The predominant students’ mental model was the initial one, followed by the synthetic and scientific level, respectively, and the adopted mental models tended to form a hierarchy based on the grade of students. The results showed that the suspending models tended to be adopted and was influenced by the mental model in the floating and sinking contexts. This result confirms the findings of previous studies, which stated that mental models depend on the context of the phenomenon being presented. The existence of variations in the students' mental models for reasoning about density and depiction of suspending objects revealed gaps in the consolidation of their mental models. In learning activities, it is not enough to teach the concepts of floating and sinking. Hence, an adequate portion for the suspending concept must be provided by depicting various object positions and emphasizing a more conceptual of density-based model. [ABSTRACT FROM AUTHOR]

Spray-dried milk powders are characterized by an underrepresentation of hydrophilic compounds on the particle surface compared to the bulk, which renders reconstitution unfavourable. To overcome this issue, in the present study we instigated the coating of whole milk powder with two types of micronized lactose: crystalline and amorphous. We demonstrate that deposition of micronized lactose on the surface of whole milk powder leads to an increase in the reconstitution rate at 21 °C, correlated with a decrease in the apparent contact angle of the material. We also show that the physical solid state of micronized lactose is an important factor influencing the reconstitution performance of coated whole milk powder; If micronized lactose is amorphous, increasing the coating concentration beyond a certain point has little or no further effect on the reconstitution kinetics, which could be explained by viscosity build-up effects that hamper capillary penetration and sinking. [Display omitted] • Dry coating of whole milk powder with micronized lactose (crystalline/amorphous) • Enhancement of powder wettability and reconstitution at 21 °C • Powder sinking is influenced by the physical solid state of the coating material [ABSTRACT FROM AUTHOR]

Sinking and horizontal movements are necessary parameters for assessing the potential impacts of surface subsidence in mining activities. Based on similarity criteria, the surface subsidence mechanism was studied using a physical model composed of similar materials such as sand, cement, and gypsum. With constant field geological parameters maintained in two angles of a coal seam, models of roof subsidence of composite rock were compared for different mining configurations. In accordance with observations from the physical model, it was concluded that subsidence and horizontal movement of strata near to and far from the coal seams were different and divided into five zones. The zone above a mined-out area underwent greater total subsidence compared to unexploited regions on both sides. Correlations between a subsidence curve and the height of a caving zone and the mining dip angle were obtained and verified from numerical model results. According to the roof’s position relative to the goaf, the area above the goaf of the composite rock layer was divided into three regions: a curving zone, a water-conducting fracture zone, and a falling zone, to which the subsidence and movement characteristics of each area could be proposed. Compared with the subsidence and movement characteristics observed from the physical and numerical model, the acquisition of subsidence characteristics and parameters in different areas can provide an idea for improvement, innovation or proposal of a theoretical formula for subsidence prediction of composite rock formations.

Aggregation between microalgae and microplastics (MPs) significantly influences the MPs distribution in marine environment. We investigated the effects of two diatoms, the planktonic Pseudo-nitzschia pungens and the periphytic Navicula sp., on the formation and sinking of aggregates when they were cultured with four different types of MPs: small and large polyethylene terephthalate (PET) fibers, and low-density and high-density polyethylene (PE) spheres. Navicula sp. formed aggregates with all MPs within one week, but P. pungens only formed aggregates with PE spheres after 9 weeks. The PE- Navicula sp. aggregates settled about 100 times faster than the PE- P. pungens aggregates (12.2 vs. 0.1 mm s−1), and this difference was most likely due to aggregate shape rather than size. Our findings indicate that the periphytic Navicula sp. had a greater effect on the settling of MPs than the planktonic P. pungens. These findings have implications for understanding the behavior of MPs in marine environments. • Periphytic diatom Navicula sp. enhances microplastic (MP) aggregation and sinking more than planktonic diatom P. pungens. • Microalga-MP aggregate shape is crucial for sinking rates, influenced by the physical environment and species specificity. • Understanding MPs dynamics in the marine environment is important, emphasizing aggregation with microalgae and sinking. [ABSTRACT FROM AUTHOR]

Phytoplankton sinking is a major component of vertical ocean carbon and nutrient fluxes, and sinking is an integral component of phytoplankton biology and ecology. Much of our understanding of phytoplankton sinking derives from the settling column method (SETCOL) in which sinking speeds are calculated from the proportion of cells reaching the bottom of a water-filled column after a set time. Video-based methods are a recent alternative to SETCOL in which sinking speeds are measured by tracking the movement of individual cells in a salinity-stratified water column. In this study, we present the results of a meta-analysis showing that SETCOL produces significantly and consistently lower sinking speeds than the video method. Next, we perform a particle image velocimetry analysis, which shows that the observed discrepancy in sinking speeds between the two methods can probably be explained by weak convection currents in the SETCOLs. Finally, we discuss the implications of these results for the interpretation of past and future phytoplankton sinking speed measurements and models that rely on those measurements., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

Sinking of microplastics (MPs) after biofouling is considered an important mechanisms responsible for the downward transport/sedimentation of MPs in the ocean and freshwaters. Previous studies demonstrated MP sinking caused by an increase in the composite density of MPs after biofouling, while MPs with smaller size or shapes with higher surface area to volume ratios (SA:V), such as films, are speculated to sink faster. In this study, we designed an in situ microcosm to simulate the ambient environmental conditions experienced by floating MPs to elucidate the biofouling and sinking of polyethylene (PE), polypropylene (PP), and expanded-polystyrene (EPS) MPs of various sizes and shapes. Our results showed smaller PE and PP MP granules sank faster than large ones. Even EPS granules of 100 μm diameter, having a much lower density (0.02 mg/mm 3 ) than water, started to sink after 2 weeks of biofouling. Moreover, PE film and fiber MPs with higher SA:V did not sink faster than PE MP granules of the same mass, implying that mechanisms other than SA:V, such as fouling contact area and drag coefficient, play a role in the regulation of biofouling and sinking of MPs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Defining the physiological traits that characterise phytoplankton involves comparison with related organisms in benthic habitats. Comparison of survival time in darkness under natural conditions requires more information. Gas vesicles and flagella as mechanisms of upward movement relative to surrounding water, allowing periodic vertical migration, are not confined to plankton, although buoyancy changes related to compositional changes of a large central vacuole may be restricted to plankton. Benthic microalgae have the same range of photosynthetic pigments as do phytoplankton; it is not clear if there are differences in the rate of regulation and acclimation of photosynthetic machinery to variations in irradiance for phytoplankton and for microphytobenthos. There are inadequate data to determine if responses to variations in frequency or magnitude of changes in the supply of inorganic carbon, nitrogen or phosphorus differ between phytoplankton and benthic microalgae. Phagophotomixotrophy and osmophotomixotrophy, occur in both phytoplankton and benthic microalgae. Further progress in identifying physiological traits specific to phytoplankton requires more experimentation on benthic microalgae that are closely related to planktonic microalgae, with attention to whether the benthic algae examined have, as far as can be determined, never been planktonic during their evolution or are derived from planktonic ancestors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Disinfections have different effects on MPs sinking behavior. • UV and ozone induce decreasing surface roughness and hydrophobicity. • These two disinfection enhance the sinking ratio and velocity of PS microspheres. • Chlorination corrodes the PS surface to generate intensive nanoscale holes. • Sinking ratio of PS microspheres dramatically declines after chlorination. Disinfection in wastewater treatment plants has potential effects on the sinking behavior of microplastics (MPs). Investigating its intrinsic mechanisms would be significant for predicting migration and transport patterns of MPs in aquatic ecosystem. In this study, polystyrene (PS) microspheres were selected as the model MP, and lab-scale ultraviolet-C (UV-C) irradiation, ozonation oxidation and chlorination were applied to simulate the disinfection processes. Furthermore, the sinking ratio and velocity experiments were performed in ultrapure water, river water and seawater. The apparent sinking velocity of PS microspheres (780 μm, ρ s = 1.05 g cm−3) was 0.849 cm s−1, which was closed to its theoretical sinking velocity (0.897 cm s−1) in ultrapure water. In UV-C and ozonation treatments, photolysis and oxidation, which generated a smoother surface containing oxygen-bonds, were the dominating decomposition mechanisms. As a result, the decreasing surface roughness and hydrophobicity contributed to enhanced sinking ratio (from 49.3% to 93.0% and 62.3%, respectively) and velocity (from 0.849 cm s−1 to 0.908 cm s−1 and 0.885 cm s−1, respectively) of PS microspheres. On the contrary, PS tended to float on the water surface after chlorination (sinking ratio decreased to < 20%), which can be due to the generation of nanoscale holes corroded by chlorine on surface. The air trapped in the nanoscale holes would increase the hydrophobicity and roughness, resulting in a surface against water wetting. In general, the sinking performance of PS microplastics was altered with different patterns depending on disinfection methods. [ABSTRACT FROM AUTHOR]

Sinking and horizontal movements are necessary parameters for assessing the potential impacts of surface subsidence in mining activities. Based on similarity criteria, the surface subsidence mechanism was studied using a physical model composed of similar materials such as sand, cement, and gypsum. With constant field geological parameters maintained in two angles of a coal seam, models of roof subsidence of composite rock were compared for different mining configurations. In accordance with observations from the physical model, it was concluded that subsidence and horizontal movement of strata near to and far from the coal seams were different and divided into five zones. The zone above a mined-out area underwent greater total subsidence compared to unexploited regions on both sides. Correlations between a subsidence curve and the height of a caving zone and the mining dip angle were obtained and verified from numerical model results. According to the roof's position relative to the goaf, the area above the goaf of the composite rock layer was divided into three regions: a curving zone, a water-conducting fracture zone, and a falling zone, to which the subsidence and movement characteristics of each area could be proposed. Compared with the subsidence and movement characteristics observed from the physical and numerical model, the acquisition of subsidence characteristics and parameters in different areas can provide an idea for improvement, innovation or proposal of a theoretical formula for subsidence prediction of composite rock formations. [ABSTRACT FROM AUTHOR]