Fresh Surface Research Articles

Effects of powder surface conditions on the rheological behavior of Ti–6Al–4 V alloy powders for additive manufacturing

Laser powder-bed fusion (L-PBF) is a promising manufacturing process for fabricating metallic parts with tailored architectures. A feedstock powder with good flowability is required to homogeneously deposit the powder on the building substrate and obtain reliable and high-quality L-PBF products. Although the effects of powder morphology and particle size on flowability have been widely investigated, the relationship between powder surface conditions and rheological behaviors is not well established. Therefore, in this study, the surface conditions of Ti–6Al–4 V alloy powders were intentionally adjusted through conventional heat treatments under different gas atmospheres. The morphology and particle size distribution of the Ti–6Al–4 V powder heat treated at 773 K in air (Air773) and Ar (Ar773) atmospheres remained unchanged compared to those of the untreated powder. However, the quantity of surface oxides on the Air773 powder increased, enhancing the decoration of surface hydroxyl groups, as illustrated by water wettability tests. By contrast, the oxide layer of the Ar773 powder decomposed and dissolved into the matrix, resulting in the generation of fresh metallic surfaces. Consequently, the flowability of the Air773 powder increased, whereas that of the Ar773 powder tended to decrease, thereby deteriorating the quality of powder beds during the recoating process. The results prove that the cohesive strength of Ti–6Al–4 V powder is more strongly determined by metallic TiTi interactions than by hydrogen bonds. Thus, the effective approach for adjusting the powder surface conditions presented in this study offers new insights into the potential for economically developing high-performance Ti alloy components by controlling the powder properties and L-PBF process.

New perspective on the depassivation mechanism of chalcopyrite by ethylene thiourea

The catalytic effect of ethylene thiourea (ETU) during the acidic ferric sulfate leaching of chalcopyrite was studied through various approaches. Bioleaching experiments showed that the addition of ETU rapidly dissolved the Cu-rich passivation layer on chalcopyrite, bringing the dissolved Cu/Fe mole ratio back to 1. Continuation of the leaching experiment shows that ETU also enhances copper extraction from depassivated chalcopyrite. Bioleaching tests carried out on pure covellite showed a similar catalytic effect from ETU. Chemical leaching tests conducted on chalcopyrite in acidic ferric/ferrous sulfate solution confirmed that the catalytic effect of ETU does not originate from changes in solution potential. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the leached chalcopyrite surfaces showed that ETU can supress the formation of a copper polysulfide phase during leaching. Ex-situ I-V analysis proved that the product layer is a p-type semiconductor and forms a diode with the n-type bulk mineral. ETU helped dissolve the p-type surface product layer and therefore transitioned the passivated chalcopyrite from a diode back to its native resistor form. Electrochemical impedance spectroscopy (EIS) analysis further demonstrated that the catalytic effect of ETU is more pronounced for passivated chalcopyrite than for a fresh surface. Combined, the results prove that ETU is an excellent remedy for passivated chalcopyrite as it readily catalyzes the dissolution of the passive layer and then continues to catalyze the leaching of native chalcopyrite.

Characterization of subsurface pathways contributing to freshwater salinization of urban streams using electrical and electromagnetic imaging techniques

Salinization of inland fresh surface waters in temperate climates is a growing concern due to increasing salt inputs from sources including chloride (Cl)-containing road salt de-icers, industrial waste, and landfill leachate. Groundwater pathways play an important role in the year-round delivery of Cl to streams, but quantifying this pathway, including spatiotemporal variability and amount of Cl mass stored in the subsurface, is challenging. The objective of this study was to demonstrate, evaluate, and compare the potential applications of the geoelectrical techniques – electromagnetics (EM) and direct current (DC) resistivity – for mapping salt contamination in shallow urban groundwater and characterizing the groundwater pathways delivering Cl to urban streams. EM and DC surveys were conducted (3D mapping and 2D time-lapse) across a 20 m salt-impacted stream section and surrounding riparian zone that is located near an arterial road and parking lot. Groundwater samples and soil cores were also collected to validate the geoelectrical results. Both the EM and DC surveys detected high salt concentrations in the shallow subsurface (up to 3 m depth) near the road, parking lot, and stream; however, DC more accurately represented groundwater Cl concentrations. DC results were used to calculate the total Cl mass in the subsurface, with the spatial mass distribution used to infer the temporal variability in the subsurface salt plume. Finally, time-lapse DC showed that the highest groundwater salt concentrations existed near the stream between June and October – this is expected to contribute to the elevated salt concentrations in the stream during summer months. This study has shown that EM and DC can be useful for identifying groundwater salt concentration, storage, and transport in a non-intrusive and efficient manner, making them valuable field tools for characterizing and quantifying groundwater salt pathways to urban streams.

Narrow host range phages infect essential bacteria for water purification reactions in groundwater-fed rapid sand filters

Biofiltration is used worldwide to provide safe potable water due to its low energy demand and excellent treatment performance. For instance, in Denmark, over 95% of drinking water is supplied through groundwater-fed rapid sand filters (RSF). Bacteriophages, viruses that infect bacteria, have been shown to shape the taxonomic and functional composition of microbial communities across a range of natural and engineering systems. However, phages in the biofiltration systems are rarely studied, despite the central role microbes play in water purification. To probe this, metagenomic data from surface water, groundwater and mixed source water biofiltration units (n = 26 from China, Europe and USA) for drinking water production were analysed to characterize prokaryotic viruses and to identify their potential microbial hosts. The source water type and geographical location are found to exert influence on the composition of the phageome in biofilters. Although the viral abundance (71,676 ± 17,841 RPKM) in biofilters is only 14.4% and 17.0% lower than those of the nutrient-rich wastewater treatment plants and fresh surface waters, the richness (1,441 ± 1,046) and diversity (Inverse Simpson: 91 ± 61) in biofiltration units are significantly less by a factor of 2–5 and 3–4, respectively. In depth analysis of data from 24 groundwater-fed RSFs in Denmark revealed a core phageome shared by most RSFs, which was consistently linked to dominant microbial hosts involved in key biological reactions for water purification. Finally, the high number of specific links detected between phages and bacterial species and the large proportion of lytic phages (77%) led to the conjecture that phages regulate bacterial populations through predation, preventing the proliferation of dominant species and contributing to the established functional redundancy among the dominant microbial groups. In conclusion, bacteriophages are likely to play a significant role in water treatment within biofilters, particularly through interactions with key bacterial species.

Boron Isotopes in Fresh Surface Waters in a Temperate Coastal Setting

The results from a four-year study of a freshwater pond on Long Island, NY, USA, do not point to a single source of boron (and by proxy other elements including nutrients) in this system. However, boron data from samples associated with this pond can be explained by mixing between average precipitation (weighted average δ11B = 22.7) in the area and the local sources of boron, both natural and anthropogenic. This multiyear study provided the opportunity to see both yearly and seasonal differences. One algae sample from the pond showed significant fractionation and enrichment in light boron relative to the water and suggests algae may act as a boron sink. This type of biological fractionation could explain an observed down-gradient trend to heavier boron isotope values in pond water, which corresponds to the slight reduction in boron concentration seen in 2021. However, the trend was subdued in the following year, likely due to differences in the water flow rates and/or rate of algal growth. An opposite trend was seen with depth in the water, where δ11B showed a positive correlation to boron concentration, which increased with depth from the surface of the pond. This gradient may be explained by the stratification of the pond with a heavy source concentrating in the bottom waters. The bottom water composition was consistent with goose feces (δ11B = 25.8) or the addition of chemicals from the application of rock salt to local roads in winter. Surprisingly, boron from seawater (average δ11B = 39.8) did not appear to have a direct impact on Setauket Pond, other than its influence on precipitation, providing heavy δ11B and very low boron concentrations.

Effect of radial, concentric scratches on a steady state heat transfer through a fin of aluminum alloy 6061

The steady state heat transfer performance of the engine cylinder fin is investigated using ANSYS’s Workbench for understanding the effect of micro-scratches. The investigation was carried to incorporate new kinds of manufacturing techniques that will help for improving the performance and save the cost. The performance was improved with number of radial or concentric scratches due to the increase in surface area exposed for convective heat transfer. The tip temperature was decreased from 791.86 °C to 728.26 °C for 480 radial scratches, while the heat flux was increased from 4.5697 × 106 to 5.0317 × 106 W/m2. In the case of concentric scratches, the tip temperature was reduced to 589.47 °C and the heat flux was enhanced to 9.8531 × 106 W/m2 for 150 concentric scratches. The concentric pattern reduced temperature drastically, while the maximum heat flux is uplifted due to the high exposure of the fresh convective surface area upon the scratching normal to the direction of heat flow. For maintaining the safety temperature and improved heat dissipation, the non-conventional manufacturing process can be adopted to reduce the cost of fin and, most importantly, the fin length.

Exploring the intricacies of machine learning-based optimization of electric discharge machining on squeeze cast TiB2/AA6061 composites: Insights from morphological, and microstructural aspects in the surface structure analysis of recast layer formation and worn-out analysis

Aluminium (Al) Alloy-6061/TiB2 was developed with Squeeze casting while varying composite quantities with titanium diboride (TiB2). The metallographic structure of the composite was investigated using EDS and scanning electron microscopy (SEM). The machining of developed composite is challenging with the conventional methods due to higher tool wear and surface roughness (Ra). This study analyses the output responses, and machinability of TiB2 of 15% volume reinforced AA6061 composites using Electrical Discharge Machining (EDM). The EDM operation variables such as current, pulse on time, and voltage gap were utilized to examine material removal rate (MRR), tool wear rate (TWR) and Ra employing Box–Behnken design of experiments. The MRR, TWR and Ra data acquired from various experiments were optimized considering single and multiple objectives by a hybrid approach. Machine learning (ML) was applied to predict responses using linear regression (LR), decision tree (DT) and random forest (RF). The samples' recast layer was examined using SEM, and the thickness of the recast layer was also documented. The Al6061 alloy's SEM micrographs reveal deep equiaxed dimples on its fracture surface, indicating a high level of plastic deformation before failure. TiB2 is evenly distributed as darker particles in the Al-matrix alloy with no directional-orientation. The Al6061-15 wt% TiB2 composites' fracture surfaces display deep dimples, ductile-fracture for Al6061 alloy due to higher plastic deformation, and cleavage facets in some areas. The aluminum alloy's wear pattern depicts long, extensive ploughing grooves with short cracks parallel to the sliding direction at the grooves' bottom. SEM micrographs in recast-layer formation have reported that molten metal ligaments break into droplets during flushing, exposing fresh surfaces. The aluminum alloy's groove width is larger compared to the composites. Thus, it can be observed that the wear tracks on the base Al6061 alloy are larger and deeper in comparison to the Al- 15 wt% TiB2 surface composites due to the presence of hard TiB2 particles. Also, the recast layer may be advantageous due to its wear-resistant properties. TiB2 has importance in an industry where components slide with each other it is used in disc brakes in automobiles. Compared to industry standards, single-objective optimization considerably enhanced the outcomes: MRR increased by 10.61%, TWR enriched by 25.91%, and Ra increased by 17.60%. According to an ANOVA, peak current contributed 87.88%, 98.18%, and 95.80% respectively to MRR, TWR, and Ra. It is requisite to investigate multi-objective optimization for EDM of Al6061-15 wt% TiB2 composites' owing to the diverse optimal factor combinations for responses. Ra was slightly increased by 1.14% due to simultaneous optimization utilizing hybrid techniques with Equal and Entropy weights, which diminished TWR by 11.74% and increased MRR by 11.66%. ML, particularly DT, improves machining performance by assisting productivity, durability, and cost-efficiency under changeable circumstances and raising forthcoming study possibilities.

Alkaline pretreatment of a polymetallic sulfide (Fe-Pb-Mn) ore containing silver increases the efficiency of cyanidation by decreasing elemental sulfur content and by exposing sulfide surfaces

Polymetallic sulfide ores are often not amenable to cyanide leaching due to the presence of several elements and minerals capable of interfering with this process. Thus, various strategies, such as chemical pretreatments, are often studied to improve the efficiency of cyanidation. Beyond the results of such strategies, it is important to understand the changes occurring on the mineral samples during these pretreatments. Herein, an alkaline pretreatment was applied to a silver concentrate (∼8 kg Ag/t) composed of polymetallic sulfides (Fe-Pb-Mn), which increased the silver extraction during subsequent cyanidation from 40% to 80% and decreased the cyanide consumption in half (from approximately 60 to 30 kg NaCN/t). X-ray diffraction (XRD) and ICP-MS indicated that the pretreatment could remove significant amounts of elemental sulfur, which is a known cyanicidal agent. The dissolution of significant amounts of sulfur was confirmed by chemical analysis, which also demonstrated that the dissolution of iron, lead, manganese, and silver were negligible during pretreatment. At surface level, X-ray photoelectron spectroscopy (XPS) demonstrated that the pretreatment exposes fresh sulfide surfaces (e. g. pyrite). In addition, the XPS spectra indicated that the pretreatment facilitated the exposure of clean mineral surfaces. The presence of cleaner surfaces suggested a more uniform and less hindered diffusion of leaching agents through the mineral. Indeed, fitting the extraction data to the shrinking core model showed that pretreated samples featured a nearly ideal diffusion-controlled process, while in the case of untreated samples this fitting was less adequate. During cyanidation of both untreated and pretreated samples, lead build-up was detected on the surface (readsorption), which suggested that this phenomenon does not affect the efficiency of a leaching process. This study highlights the importance of combining bulk analytical methods with surface-sensitive techniques to obtain a more complete understanding of leaching processes.

Benthic foraminifera and gromiids from oxygen-depleted environments – survival strategies, biogeochemistry and trophic interactions

Abstract. The oceans are losing oxygen (O2), and oxygen minimum zones are expanding due to climate warming (lower O2 solubility) and eutrophication related to agriculture. This trend is challenging for most marine taxa that are not well adapted to O2 depletion. For other taxa this trend might be advantageous because they can withstand low O2 concentrations or thrive under O2-depleted or even anoxic conditions. Benthic foraminifera are a group of protists that include taxa with adaptations to partly extreme environmental conditions. Several species possess adaptations to O2 depletion that are rare amongst eukaryotes, and these species might benefit from ongoing ocean deoxygenation. In addition, since some foraminifera can calcify even under anoxic conditions, they are important archives for paleoceanographic reconstruction in O2-depleted environments. This paper reviews the current state of knowledge about foraminifera from low-O2 environments. Recent advances in our understanding of specific survival strategies of foraminifera to withstand O2 depletion are summarized and discussed. These adaptations include an anaerobic metabolism, heterotrophic denitrification, symbiosis with bacteria, kleptoplasty and dormancy and have a strong impact on their preferred microhabitat in the sediments, especially the ability of some benthic foraminiferal species to denitrify. Benthic foraminifera also differ regarding their trophic strategies, which has an additional impact on the selection of their microhabitat. For example, some species are strict herbivores that feed exclusively on fresh phytodetritus and live close to the sediment surface, while some species are non-selective detrivores that occupy intermediate to deep infaunal habitats. There is evidence that foraminifers have the capacity to undergo phagocytosis, even under anoxia, and some foraminiferal species which can withstand low-O2 conditions seem to prey on meiofauna. Also, due to their high abundances in O2-depleted environments and their metabolic adaptations, benthic foraminifera are key players in marine nutrient cycling, especially within the marine N and P cycles. This review summarizes the denitrification rates for the species that are known to denitrify and the intracellular nitrate concentrations of the species that are known to intracellularly store nitrate. Finally, equations are provided that can be used to estimate the intracellular nutrient storage and denitrification rates of foraminifera and might be integrated into biogeochemical models.

Elevation and thickness of the 11–10 Kyr old ‘Sinkholes Salt’ layer in the Dead Sea: clues to past limnology, paleo-bathymetry and lake levels

The sinkholes along the Dead Sea (DS) shores form by dissolution of an 11–10 kyr old subsurface salt layer (hereafter named the ‘Sinkholes Salt’) that precipitated on the lake’s floor during periods of negative water balance, water level decline and salinity increase. We analyze the variations in absolute elevation and thickness of this layer in 40 boreholes along the western shores of the DS, reconstruct water-body stratification, past lake levels, and paleo-bathymetry during salt deposition, and comment on the role of the salt-layer elevation in future sinkhole formation. In the northern basin of the DS, maximum thickness of salt (~ 23 m) is found where salt top and bottom elevations are below ~ 440 meters below sea level (mbsl) and ~ 465 mbsl, respectively. Above these elevations the salt layer gradually thins out until 416 mbsl, above which it is no longer found. These relationships suggest that thermohaline stratification, with a thermocline at 25–30 m depth, similar to the present day dynamics of the DS, developed annually during the salt-precipitation period, giving rise to uniform salt accumulation below the thermocline and partial to full dissolution above it. Salt accumulation was controlled by the bathymetry of the lake and its configuration relative to the thermocline, and locally hampered by discharge of subaqueous under-saturated groundwater. The truncation of the salt layer at elevation of 416 mbsl is attributed to salt dissolution down to this elevation by a relatively diluted upper water layer that developed following inflow of fresh surface water at the end of the salt period. This event also marks the change to a positive water balance and lake level rise from its lowest stand of ~ 405 mbsl, as determined from limnological considerations.

Effect of mechano-chemical activation with NaF on improved acid leaching of vanadium-bearing shale

Vanadium extraction from vanadium-bearing shale by direct acid leaching is currently restricted owing to the inefficient release of vanadium from mica, which consumes a large amount of acid. To overcome this limitation, this study developed a mechano-chemical activation-assisted acid-leaching process. Further, the effects of the mechano-chemical activation parameters on the vanadium-bearing shale and vanadium dissolution in an acid system were examined using the following conditions: ball-to-pulp ratio: 50 to 1, pulp density: 50%, NaF activator: 5 wt%, activation time: 30 min, sulfuric acid concentration: 12 vol%, leaching time: 6 h, leaching temperature: 95 °C. These conditions increased the vanadium leaching efficiency from 82.3% to 90.3%. The mechano-chemical activation treatment exposed the fresh muscovite surface, promoting the preferential adsorption of fluoride to form stable SiF and AlF bonds. This behavior induced a beneficial reaction surface on muscovite with a low energy barrier for subsequent leaching. During the leaching process, the weakened SiO and AlO bonds could be more easily broken by H+ attack, thus accelerating muscovite dissolution and boosting the vanadium leaching efficiency.

Timing of carbon uptake by oceanic crust determined by rock reactivity

Abstract Carbonate formation during the alteration of oceanic crust is a global CO2 sink. Its timing and controls are not well understood, particularly in volcanic seamounts, which react with seawater over tens of millions of years. We report in situ U-Pb age dates of carbonate vein and void fill in 50–74 Ma basaltic basement of the Louisville Seamount Chain. More than 90% of the carbonate formed <20 m.y. after seamount emplacement. Vesicle carbonate precipitated within 8 m.y. (median = 2.9 m.y.) whereas vein carbonate grew over longer time spans (median = 8.1 m.y.). The duration of carbonation was hence limited despite the basement’s long-term exposure to seawater. The age dates imply a rapid infill of vesicles by alteration of confined domains around vesicles. Carbonate formation in veins extended for longer periods of time, likely due to the late opening of fractures, which exposed fresh reactive rock surface to circulating seawater long after the formation of the basement. We suggest that carbonate growth ceased after the volcanic rocks were too altered to liberate sufficient Ca2+ and generate the alkalinity required for carbonate precipitation. A critical extent of rock reactivity is required to sustain carbonate formation. Carbonate precipitation likely ends after much of the exposed basaltic substrate has been altered and the rock reactivity drops below this critical threshold. These findings help to explain the generally short duration of carbonation in the flanks of mid-ocean ridges.

Sintering and agglomeration characteristics of industrially prepared CaMn0.5Ti0.375Fe0.125O3-δ perovskite oxygen carrier in chemical looping combustion

The development of oxygen carrier particles that can be prepared on an industrial scale with good cycling stability remains a challenge in the field of chemical looping. In this work, a perovskite oxygen carrier (CaMn0.5Ti0.375Fe0.125O3-δ) was prepared by an industrial-scale spray drying granulation and tested on a fluidized bed thermogravimetric analyzer for long-term chemical looping combustion. The results showed that the attrition of oxygen carrier particles originated from irregular parts of the fresh particle surface early in the cycle, and the chemical stress on particles gradually increased with the number of redox cycles, increasing the attrition and sintering of the particles. In addition, as the cycle proceeds, the perovskite structure was destroyed and the oxygen carrier reacted chemically with the quartz tube wall and the air distribution plate leading to bonding. The deep redox cycling reactions indicated that agglomeration of particles occurred mainly in the reduction stage, with the bed entering repeated periods of defluidization during the 37th-43rd and 47th-55th cycles due to the changes in particle bonding and bed pressure. Fixed bed experiment showed that particle activation came from an increase in the active area of the particles during the cycle, independent of whether they were fluidized or not. In addition, agglomeration started at the contact surface between the air distribution plate and the particles, resulting in blocked oxidation of the particles and deepening agglomeration due to excessive reduction of the particles.

Hydrogeochemical characterization and CO2 consumption in the Maqu catchment of the Qinghai-Tibetan Plateau by multiple hydrogeochemical methods

The Qinghai-Tibetan Plateau (TP) is the source of many large Asian rivers and has significant social, ecological and economic importance. However, few hydrogeochemistry and stable isotope studies have been performed in the Maqu catchment of the eastern TP. In this study, the hydrogeochemical composition and stable isotopes (δD and δ18O) of surface water and groundwater samples collected in the Maqu catchment were analysed to characterise the surface water and groundwater, investigate the contributions of different sources, and determine CO2 consumptions. Different techniques were used, including inverse modelling, end member mixing analysis (EMMA), and a forward mass balance model. The results indicated that all water samples are of the HCO3-Ca type. Both the surface water and groundwater are of meteoric origin and there is close contact between them (except wetlands). Water in the wetlands is substantially evaporated (0–45%). Calcite and illite generally precipitate, whereas chlorite and CO2 generally dissolve along groundwater flow paths in the east. The mean contributions of fresh surface waters, mountain-front groundwaters, and anthropogenic inputs to the surface water samples are 56%, 16%, and 28%, respectively. Carbonate and silicate weathering are the dominant sources of major cations. Moreover, high CO2 consumption rates in both the surface runoff and groundwater make the Maqu catchment an important carbon sink in the Yellow River Basin. With many newly-found conclusions on the Maqu catchment, the present study not only provides insight into the catchment but also contributes to a comprehensive understanding of the water cycle and CO2 consumptions on the TP.

Tribological Mechanism of Graphene and Ionic Liquid Mixed Fluid on Grinding Interface under Nanofluid Minimum Quantity Lubrication

Graphene has superhigh thermal conductivity up to 5000 W/(m·K), extremely thin thickness, superhigh mechanical strength and nano-lamellar structure with low interlayer shear strength, making it possess great potential in minimum quantity lubrication (MQL) grinding. Meanwhile, ionic liquids (ILs) have higher thermal conductivity and better thermal stability than vegetable oils, which are frequently used as MQL grinding fluids. And ILs have extremely low vapor pressure, thereby avoiding film boiling in grinding. These excellent properties make ILs also have immense potential in MQL grinding. However, the grinding performance of graphene and ionic liquid mixed fluid under nanofluid minimum quantity lubrication (NMQL), and its tribological mechanism on abrasive grain/workpiece grinding interface, are still unclear. This research firstly evaluates the grinding performance of graphene and ionic liquid mixed nanofluids (graphene/IL nanofluids) under NMQL experimentally. The evaluation shows that graphene/IL nanofluids can further strengthen both the cooling and lubricating performances compared with MQL grinding using ILs only. The specific grinding energy and grinding force ratio can be reduced by over 40% at grinding depth of 10 μm. Workpiece machined surface roughness can be decreased by over 10%, and grinding temperature can be lowered over 50 ℃ at grinding depth of 30 μm. Aiming at the unclear tribological mechanism of graphene/IL nanofluids, molecular dynamics simulations for abrasive grain/workpiece grinding interface are performed to explore the formation mechanism of physical adsorption film. The simulations show that the grinding interface is in a boundary lubrication state. IL molecules absorb in groove-like fractures on grain wear flat face to form boundary lubrication film, and graphene nanosheets can enter into the grinding interface to further decrease the contact area between abrasive grain and workpiece. Compared with MQL grinding, the average tangential grinding force of graphene/IL nanofluids can decrease up to 10.8%. The interlayer shear effect and low interlayer shear strength of graphene nanosheets are the principal causes of enhanced lubricating performance on the grinding interface. EDS and XPS analyses are further carried out to explore the formation mechanism of chemical reaction film. The analyses show that IL base fluid happens chemical reactions with workpiece material, producing FeF2, CrF3, and BN. The fresh machined surface of workpiece is oxidized by air, producing NiO, Cr2O3 and Fe2O3. The chemical reaction film is constituted by fluorides, nitrides and oxides together. The combined action of physical adsorption film and chemical reaction film make graphene/IL nanofluids obtain excellent grinding performance.

Balancing Volume, Temperature, and Salinity Budgets During 2014–2018 in the Tropical Pacific Ocean State Estimate

AbstractA state estimate of the tropical Pacific Ocean is used to analyze regional volume, temperature, and salinity budgets during 2014–2018. The simulated ocean state is constrained by both model dynamics and assimilated observations. Comparisons with independent mooring data show that the state estimate is consistent with the observed variability in temperature and velocity. Budgets are analyzed between 5°S and 5°N in the upper 300 m, inside a box defined to represent the central and eastern equatorial Pacific. Transports through the faces of this box are quantified to understand the processes responsible for variability in box‐mean properties. Vertical mixing across 300 m is negligible; temperature and salinity tendencies are balanced by surface fluxes and advective divergence, which is decomposed into geostrophic and ageostrophic components. The onset and recovery of the 2015/2016 El Niño event is found to be dominated by anomalous surface fluxes and horizontal advection. During the onset phase, weaker trade winds cause the shallow meridional overturning circulation to slow down, which reduces the poleward transport of heat and leads to upper ocean warming. Anomalous precipitation and advection of fresh water from the western Pacific drive the net freshening of the region. Relaxation from El Niño conditions is dominated by wind‐driven meridional advection at 5°N. As the meridional advection regains strength, Ekman advection efficiently exports the warm, fresh surface water out of the equatorial region. Quantifying the heat and salt transport changes in response to wind variability strengthens our understanding of global ocean heat transport.

European concept of ecologically balanced nature management in a market economy

The main task of the article is to establish the cause-and-effect links between the factors of environmental pollution and motivational mechanisms for ecologization of the economy in accordance with the concept of sustainable development. It is determined that the specificity of agricultural production is their close connection with the environment and its significant pollution with greenhouse gases and other harmful substances. It is established that the rate of global warming can be decreased by half by reducing the production of animal and plant products and increasing the use of renewable energy sources in the production sector. It is found that in the process of economic transformation, considerable attention should be paid to the need to reduce energy intensity, material intensity, ecologization of technological processes and improvement of product quality. In the realization of economic policy, the priority should be the use of environmental mechanisms for its regulation, and production should be concerned not only with satisfying the needs of consumers of products, but also with reducing the negative impact on ecosystems. The dynamics of total emissions into the atmosphere by households in a number of European countries is determined and the main reasons for such changes are indicated. A systematic analysis of the indicators that characterize the volume of fresh surface and groundwater intake per capita is carried out and the depth of the water crisis in the EU countries is determined. The article analyses the level of waste disposal and recommends the most effective waste management technologies, and studies the dynamics of changes in the area of protected forests in Europe to identify the tree species that are the best cleaners of the air. The size of compensatory contributions of countries under global climate commitments and indicators of total environmental transfers for environmental protection activities are researched. An integrated approach is used to determine the real impact of various types of economic activity of European countries on the environment. It is recommended to study and implement the experience of European market economies regarding the conceptual principles of balanced environmental management in Ukraine.

Distinct bacterial population dynamics and disease dissemination after biofilm dispersal and disassembly.

Microbial communities that form surface-attached biofilms must release and disperse their constituent cells into the environment to colonize fresh sites for continued survival of their species. For pathogens, biofilm dispersal is crucial for microbial transmission from environmental reservoirs to hosts, cross-host transmission, and dissemination of infections across tissues within the host. However, research on biofilm dispersal and its consequences in colonization of fresh sites remain poorly understood. Bacterial cells can depart from biofilms via stimuli-induced dispersal or disassembly due to direct degradation of the biofilm matrix, but the complex heterogeneity of bacterial populations released from biofilms rendered their study difficult. Using a novel 3D-bacterial "biofilm-dispersal-then-recolonization" (BDR) microfluidic model, we demonstrated that Pseudomonas aeruginosa biofilms undergo distinct spatiotemporal dynamics during chemical-induced dispersal (CID) and enzymatic disassembly (EDA), with contrasting consequences in recolonization and disease dissemination. Active CID required bacteria to employ bdlA dispersal gene and flagella to depart from biofilms as single cells at consistent velocities but could not recolonize fresh surfaces. This prevented the disseminated bacteria cells from infecting lung spheroids and Caenorhabditis elegans in on-chip coculture experiments. In contrast, EDA by degradation of a major biofilm exopolysaccharide (Psl) released immotile aggregates at high initial velocities, enabling the bacteria to recolonize fresh surfaces and cause infections in the hosts efficiently. Hence, biofilm dispersal is more complex than previously thought, where bacterial populations adopting distinct behavior after biofilm departure may be the key to survival of bacterial species and dissemination of diseases.

Molecular complexity and diversity of persistent soil organic matter

Managing and increasing organic matter in soil requires greater understanding of the mechanisms driving its persistence through resistance to microbial decomposition. Conflicting evidence exists for whether persistent soil organic matter (SOM) is molecularly complex and diverse. As such, this study used a novel application of graph networks with pyrolysis-gas chromatography-mass spectrometry to quantify the complexity and diversity of persistent SOM, defined as SOM that persists through time (soil radiocarbon age) and soil depth. We analyzed soils from the Cooloola giant podzol chronosequence across a large gradient of soil depths (0–15 m) and SOM radiocarbon ages (modern to 19,000 years BP). We found that the most persistent SOM on this gradient was highly aromatic and had the lowest molecular complexity and diversity. By contrast, fresh surface SOM had higher molecular complexity and diversity, with high contributions of plant-derived lignins and polysaccharides. These findings indicate that persisting SOM declines in molecular complexity and diversity over geological timescales and soil depths, with aromatic SOM compounds persisting longer with mineral association.

Dumping military waste into Lake Superior: the historic legacies of secrecy, censorship, and uncertainty

In recent years, the issue of military waste disposal in oceans and seas has gained significant attention; however, the impact of such waste in freshwater deposits has been understudied. The Laurentian Great Lakes of North America contain 20% of the world’s fresh surface water and are particularly vulnerable to environmental stressors such as climate change, invasive species, and toxic chemicals, making the examination of military waste management in these waters crucial. This interdisciplinary study aims to investigate the legacy of two military waste disposal sites in Lake Superior, referred to as Site A (containing barrels) and Site B (containing bullets). Both are located within the ceded territories of the Ojibwe. Despite being in close proximity, these sites have had vastly different outcomes in terms of public concern, state and federal regulatory actions, and tribal restoration efforts. Based on this observation, this study aims to answer the following questions: How did these differences develop? How did military secrecy and the loss of memory influence the management of underwater military waste at each site? How do uncertainties and rumors continue to influence citizen concern and agency management of military waste? We argue for the importance of investigating the environmental legacies of underwater military waste in order to protect inland freshwater resources worldwide.