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by Ivan Netšipailo, Lauri Aarik, Jekaterina Kozlova, Aivar Tarre, Maido Merisalu, Kaisa Aab, Hugo Mändar, Peeter Ritslaid and Väino Sammelselg

Corros. Mater. Degrad. 2025, 6(3), 36; https://doi.org/10.3390/cmd6030036 (registering DOI) - 2 Aug 2025

Abstract

We investigated the protective properties of ultrathin laminated coatings, comprising three pairs of Al₂O₃ and TiO₂ sublayers with coating thicknesses < 150 nm, deposited on AISI 310 stainless steel (SS) and Si (100) substrates at 80–500 °C by atomic layer deposition. The coatings were chemically etched and subjected to corrosion, ultrasound, and thermal shock tests. The coating etching resistance efficiency (R_e) was determined by measuring via XRF the change in the coating sublayer mass thickness after etching in hot 80% H₂SO₄. The maximum R_e values of ≥98% for both alumina and titania sublayers were obtained for the laminates deposited at 250–400 °C on both substrates. In these coatings, the titania sublayers were crystalline. The lowest R_e values of 15% and 50% for the alumina and titania sublayers, respectively, were measured for laminate grown at 80 °C on silicon. The coatings deposited at 160–200 °C demonstrated a delay in the increase of R_e values, attributed to the changes in the titania sublayers before full crystallization. Coatings grown at higher temperatures were also more resistant to ultrasound and liquid nitrogen treatments. In contrast, coatings deposited at 125 °C on SS had better corrosion protection, as demonstrated via electrochemical impedance spectroscopy and a standard immersion test in FeCl₃ solution. Full article

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23 pages, 2663 KiB

Open AccessArticle

How Nanofluids May Enhance Energy Efficiency and Carbon Footprint in Buildings?

by Sylwia Wciślik

Sustainability 2025, 17(15), 7035; https://doi.org/10.3390/su17157035 (registering DOI) - 2 Aug 2025

Abstract

Nanofluids are an innovative working medium in solar hot water installations (DHWs), thanks to their increased thermal conductivity and heat transfer coefficient. The aim of this work was to assess the effect of Al₂O₃ nanofluids in a water–ethylene glycol base (40:60%) and with the addition of Tween 80 surfactant (0.2 wt%) on thermal efficiency (ε) and exergy (η_ex) in a plate heat exchanger at DHW flows of 3 and 12 L/min. The numerical NTU–ε model was used with dynamic updating of thermophysical properties of nanofluids and the solution of the ODE system using the ode45 method, and the validation was carried out against the literature data. The results showed that the nanofluids achieved ε ≈ 0.85 (vs. ε ≈ 0.87 for the base fluid) and η_ex ≈ 0.72 (vs. η_ex ≈ 0.74), with higher entropy generation. The addition of Tween 80 reduced the viscosity by about 10–15%, resulting in a slight increase of Re and h-factor; however, the impact on ε and η_ex was marginal. The environmental analysis with an annual demand of Q = 3000 kWh/year and an emission factor of 0.2 kg CO₂/kWh showed that for ε < 0.87 the nanofluids increased the emissions by ≈16 kg CO₂/year, while at ε ≈ 0.92, a reduction of ≈5% was possible. This paper highlights the need to optimize nanofluid viscosity and exchanger geometry to maximize energy and environmental benefits. Nowadays, due to the growing problems of global warming, the analysis of energy efficiency and carbon footprint related to the functioning of a building seems to be crucial. Full article

(This article belongs to the Special Issue Green Building Intelligence: Evaluating Energy Efficiency and Renewable Energy Solutions)

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25 pages, 7588 KiB

Open AccessArticle

Electrophoretic Deposition of Green-Synthesized Hydroxyapatite on Thermally Oxidized Titanium: Enhanced Bioactivity and Antibacterial Performance

by Mariana Relva, Daniela Santo, Ricardo Alexandre, Pedro Faia, Sandra Carvalho, Zohra Benzarti and Susana Devesa

Appl. Sci. 2025, 15(15), 8598; https://doi.org/10.3390/app15158598 (registering DOI) - 2 Aug 2025

Abstract

Titanium alloys such as Ti-6Al-4V are widely used in biomedical implants due to their excellent mechanical properties and biocompatibility, but their bioinert nature limits osseointegration and antibacterial performance. This study proposes a multifunctional surface coating system integrating a thermally oxidized TiO₂ interlayer with a hydroxyapatite (HAp) top layer synthesized via a green route using Hylocereus undatus extract. The HAp was deposited by electrophoretic deposition (EPD), enabling continuous coverage and strong adhesion to the pre-treated Ti-6Al-4V substrate. Structural, morphological, chemical, and electrical characterizations were performed using XRD, SEM, EDS, Raman spectroscopy, and impedance spectroscopy. Bioactivity was assessed through apatite formation in simulated body fluid (SBF), while antibacterial properties were evaluated against Staphylococcus aureus. The results demonstrated successful formation of crystalline TiO₂ (rutile phase) and calcium-rich HAp with good surface coverage. The HAp-coated surfaces exhibited significantly enhanced bioactivity and strong antibacterial performance, likely due to the combined effects of surface roughness and the bioactive compounds present in the plant extract. This study highlights the potential of eco-friendly, bio-inspired surface engineering to improve the biological performance of titanium-based implants. Full article

(This article belongs to the Special Issue Sustainable Nanomaterials for Biotechnological and Medical Applications: Current Developments)

24 pages, 8010 KiB

Open AccessArticle

Mono-(Ni, Au) and Bimetallic (Ni-Au) Nanoparticles-Loaded ZnAlO Mixed Oxides as Sunlight-Driven Photocatalysts for Environmental Remediation

by Monica Pavel, Liubovi Cretu, Catalin Negrila, Daniela C. Culita, Anca Vasile, Razvan State, Ioan Balint and Florica Papa

Molecules 2025, 30(15), 3249; https://doi.org/10.3390/molecules30153249 (registering DOI) - 2 Aug 2025

Abstract

A facile and versatile strategy to obtain NPs@ZnAlO nanocomposite materials, comprising controlled-size nanoparticles (NPs) within a ZnAlO matrix is reported. The mono-(Au, Ni) and bimetallic (Ni-Au) NPs serving as an active phase were prepared by the polyol-alkaline method, while the ZnAlO support was obtained via the thermal decomposition of its corresponding layered double hydroxide (LDH) precursors. X-ray diffraction (XRD) patterns confirmed the successful fabrication of the nanocomposites, including the synthesis of the metallic NPs, the formation of LDH-like structure, and the subsequent transformation to ZnO phase upon LDH calcination. The obtained nanostructures confirmed the nanoplate-like morphology inherited from the original LDH precursors, which tended to aggregate after the addition of gold NPs. According to the UV-Vis spectroscopy, loading NPs onto the ZnAlO support enhanced the light absorption and reduced the band gap energy. ATR-DRIFT spectroscopy, H₂-TPR measurements, and XPS analysis provided information about the functional groups, surface composition, and reducibility of the materials. The catalytic performance of the developed nanostructures was evaluated by the photodegradation of bisphenol A (BPA), under simulated solar irradiation. The conversion of BPA over the bimetallic Ni-Au@ZnAlO reached up to 95% after 180 min of irradiation, exceeding the monometallic Ni@ZnAlO and Au@ZnAlO catalysts. Its enhanced activity was correlated with good dispersion of the bimetals, narrower band gap, and efficient charge carrier separation of the photo-induced e⁻/h⁺ pairs. Full article

(This article belongs to the Special Issue Advances in Metal/Oxide Interfacial Catalysts: Design, Properties, and Applications)

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21 pages, 2240 KiB

Open AccessReview

A Review of Fluorescent pH Probes: Ratiometric Strategies, Extreme pH Sensing, and Multifunctional Utility

by Weiqiao Xu, Zhenting Ma, Qixin Tian, Yuanqing Chen, Qiumei Jiang and Liang Fan

Chemosensors 2025, 13(8), 280; https://doi.org/10.3390/chemosensors13080280 (registering DOI) - 2 Aug 2025

Abstract

pH is a critical parameter requiring precise monitoring across scientific, industrial, and biological domains. Fluorescent pH probes offer a powerful alternative to traditional methods (e.g., electrodes, indicators), overcoming limitations in miniaturization, long-term stability, and electromagnetic interference. By utilizing photophysical mechanisms—including intramolecular charge transfer (ICT), photoinduced electron transfer (PET), and fluorescence resonance energy transfer (FRET)—these probes enable high-sensitivity, reusable, and biocompatible sensing. This review systematically details recent advances, categorizing probes by operational pH range: strongly acidic (0–3), weakly acidic (3–7), strongly alkaline (>12), weakly alkaline (7–11), near-neutral (6–8), and wide-dynamic range. Innovations such as ratiometric detection, organelle-specific targeting (lysosomes, mitochondria), smartphone colorimetry, and dual-analyte response (e.g., pH + Al³⁺/CN⁻) are highlighted. Applications span real-time cellular imaging (HeLa cells, zebrafish, mice), food quality assessment, environmental monitoring, and industrial diagnostics (e.g., concrete pH). Persistent challenges include extreme-pH sensing (notably alkalinity), photobleaching, dye leakage, and environmental resilience. Future research should prioritize broadening functional pH ranges, enhancing probe stability, and developing wide-range sensing strategies to advance deployment in commercial and industrial online monitoring platforms. Full article

(This article belongs to the Special Issue Advancements and Emerging Applications of Fluorescent Probes for Sensing and Imaging)

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4 pages, 188 KiB

Open AccessCorrection

Correction: Mancuso et al. Forcing Ahead: Second-Line Treatment Options for Lenalidomide-Refractory Multiple Myeloma. Cancers 2025, 17, 1168

by Katia Mancuso, Simona Barbato, Francesco Di Raimondo, Francesca Gay, Pellegrino Musto, Massimo Offidani, Maria Teresa Petrucci, Elena Zamagni, Renato Zambello and Michele Cavo

Cancers 2025, 17(15), 2555; https://doi.org/10.3390/cancers17152555 (registering DOI) - 1 Aug 2025

Abstract

The authors have separated the affiliations originally listed in affiliation 4—this is so both affiliations can be organized from subordinate to superior [...] Full article

(This article belongs to the Section Cancer Therapy)

13 pages, 680 KiB

Open AccessArticle

Anthropometric Characteristics and Somatotype of Young Slovenian Tennis Players

by Ales Germic, Tjasa Filipcic and Ales Filipcic

Appl. Sci. 2025, 15(15), 8584; https://doi.org/10.3390/app15158584 (registering DOI) - 1 Aug 2025

Abstract

Tennis is a demanding sport that requires physical abilities and optimal body composition. The aim of this study was to investigate the anthropometric characteristics, body composition, and somatotype development of young Slovenian tennis players (754 boys and 514 girls aged 12 to 18 years) over the last two decades. Using standardised anthropometric measurements and the Heath-Carter method, somatotypes were calculated and analysed by age and gender. The results showed clear age- and gender-specific trends and differences in both somatotype profiles and detailed anthropometric characteristics. Significant differences were found in height, body mass, BMI, skinfolds, girths, and limb lengths, with gender differences becoming more pronounced in the older age groups. In boys, mesomorphy increased with age, reflecting an increase in musculature, while in girls, a shift from ectomorphic to endomorphic profiles was observed during adolescence, probably influenced by pubertal and hormonal changes. Significant sex-specific differences were observed in all three somatotype components in most age groups, especially in fat mass and muscle. The longitudinal design provides valuable data and insights into the evolving physical profiles of adolescent tennis players that support more effective talent identification and training. Despite the changes that have taken place in tennis over time, standardised measurement protocols ensured comparability, making the results relevant for practitioners working with adolescents in tennis development. Full article

(This article belongs to the Special Issue Human Performance and Health in Sport and Exercise—2nd Edition)

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13 pages, 2583 KiB

Open AccessArticle

Hierarchical Flaky Spinel Structure with Al and Mn Co-Doping Towards Preferable Oxygen Evolution Performance

by Hengfen Shen, Hao Du, Peng Li and Mei Wang

Materials 2025, 18(15), 3633; https://doi.org/10.3390/ma18153633 (registering DOI) - 1 Aug 2025

Abstract

As an efficient clean energy technology, water electrolysis for hydrogen production has its efficiency limited by the sluggish oxygen evolution reaction (OER) kinetics, which drives the demand for the development of high-performance anode OER catalysts. This work constructs bimetallic (Al, Mn) co-doped nanoporous spinel CoFe₂O₄ (np-CFO) with a tunable structure and composition as an OER catalyst through a simple two-step dealloying strategy. The as-formed np-CFO (Al and Mn) features a hierarchical flaky configuration; that is, there are a large number of fine nanosheets attached to the surface of a regular micron-sized flake, which not only increases the number of active sites but also enhances mass transport efficiency. Consequently, the optimized catalyst exhibits a low OER overpotential of only 320 mV at a current density of 10 mA cm⁻², a minimal Tafel slope of 45.09 mV dec⁻¹, and exceptional durability. Even under industrial conditions (6 M KOH, 60 °C), it only needs 1.83 V to achieve a current density of 500 mA cm⁻² and can maintain good stability for approximately 100 h at this high current density. Theoretical simulations indicate that Al and Mn co-doping could indeed optimize the electronic structure of CFO and thus decrease the energy barrier of OER to 1.35 eV. This work offers a practical approach towards synthesizing efficient and stable OER catalysts. Full article

(This article belongs to the Special Issue High-Performance Materials for Energy Conversion)

17 pages, 2410 KiB

Open AccessArticle

Microstructural Characterisation of Bi-Ag-Ti Solder Alloy and Evaluation of Wettability on Ceramic and Composite Substrates Joined via Indirect Electron Beam Heating in Vacuum

by Mikulas Sloboda, Roman Kolenak, Tomas Melus, Peter Gogola, Matej Pasak, Daniel Drimal and Jaromir Drapala

Materials 2025, 18(15), 3634; https://doi.org/10.3390/ma18153634 (registering DOI) - 1 Aug 2025

Abstract

This paper examines the wettability and interactions between ceramic and composite materials soldered with Bi-based solder containing 11 wt.% of silver and 3 wt.% titanium using indirect electron beam soldering technology. The Bi11Ag3Ti solder, with a melting point of 402 °C, consisted of a bismuth matrix containing silver lamellae. Titanium, acting as an active element, positively influenced the interaction between the solder and the joined materials. SiC and Ni-SiC substrates were soldered at temperatures of 750 °C, 850 °C, and 950 °C. Measurements of wettability angles indicated that the lowest value (20°) was achieved with SiC substrates at 950 °C. A temperature of 750 °C appeared to be the least suitable for both substrates and was entirely unsuitable for Ni-SiC. It was also observed that the Bi11Ag3Ti solder wetted the SiC substrates more effectively than Ni-SiC substrates. The optimal working temperature for this solder was determined to be 950 °C. The shear strength of the joints soldered with the Bi11Ag3Ti alloy was 23.5 MPa for the Al₂O₃/Ni-SiC joint and 9 MPa for the SiC/Ni-SiC joint. Full article

(This article belongs to the Special Issue Advanced Materials and Processing Technologies)

27 pages, 872 KiB

Open AccessArticle

Effect of Monomer Mixture Composition on TiCl₄-Al(i-C₄H₉)₃ Catalytic System Activity in Butadiene–Isoprene Copolymerization: A Theoretical Study

by Konstantin A. Tereshchenko, Rustem T. Ismagilov, Nikolai V. Ulitin, Yana L. Lyulinskaya and Alexander S. Novikov

Computation 2025, 13(8), 184; https://doi.org/10.3390/computation13080184 (registering DOI) - 1 Aug 2025

Abstract

Divinylisoprene rubber, a copolymer of butadiene and isoprene, is used as raw material for rubber technical products, combining isoprene rubber’s elasticity and butadiene rubber’s wear resistance. These properties depend quantitatively on the copolymer composition, which depends on the kinetics of its synthesis. This work aims to theoretically describe how the monomer mixture composition in the butadiene–isoprene copolymerization affects the activity of the TiCl₄–Al(i-C₄H₉)₃ catalytic system (expressed by active sites concentration) via kinetic modeling. This enables development of a reliable kinetic model for divinylisoprene rubber synthesis, predicting reaction rate, molecular weight, and composition, applicable to reactor design and process intensification. Active sites concentrations were calculated from experimental copolymerization rates and known chain propagation constants for various monomer compositions. Kinetic equations for active sites formation were based on mass-action law and Langmuir monomolecular adsorption theory. An analytical equation relating active sites concentration to monomer composition was derived, analyzed, and optimized with experimental data. The results show that monomer composition’s influence on active sites concentration is well described by a two-step kinetic model (physical adsorption followed by Ti–C bond formation), accounting for competitive adsorption: isoprene adsorbs more readily, while butadiene forms more stable active sites. Full article

(This article belongs to the Special Issue Feature Papers in Computational Chemistry)

18 pages, 3224 KiB

Open AccessArticle

Design of Experiments Approach for Efficient Heavy Metals Stabilization Using Metakaolin-Based Geopolymers

by Raffaele Emanuele Russo, Elisa Santoni, Martina Fattobene, Mattia Giovini, Francesco Genua, Cristina Leonelli, Isabella Lancellotti, Ana Herrero and Mario Berrettoni

Molecules 2025, 30(15), 3235; https://doi.org/10.3390/molecules30153235 (registering DOI) - 1 Aug 2025

Abstract

Alkali-activated aluminosilicate matrices are increasingly studied for their ability to stabilize hazardous metal contaminants via alkali activation at room temperature. In this study, metakaolin-based geopolymers were used to immobilize chromium and nickel salts, with systematic variation of key synthesis parameters, Na/Al molar ratio, metal concentration, anion type, and alkaline solution aging time, which have not been previously studied. A Design of Experiments approach was employed to study the effect of factors on metal leaching behavior and to better understand the underlying immobilization mechanisms. The analysis revealed that higher Na/Al ratios significantly enhance geopolymerization and reduce metal release, as supported by FTIR spectral shifts and decreased shoulder intensity. Notably, aging time had an influence on chromium behavior due to its effect on early silicate network formation, which can hinder the incorporation of chromium species. All tested formulations achieved metal immobilization rates of 98.8% or higher for both chromium and nickel. Overall, this study advances our understanding of geopolymer-based heavy metal immobilization. Full article

(This article belongs to the Special Issue Green Chemistry Approaches to Analysis and Environmental Remediation)

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1 pages, 121 KiB

Open AccessCorrection

Correction: Hernández-Juárez et al. Low-Frequency Acoustic Emissions During Granular Discharge in Inclined Silos. Fluids 2025, 10, 138

by Josué Roberto Hernández-Juárez, Abel López-Villa, Abraham Medina and Daniel Armando Serrano Huerta

Fluids 2025, 10(8), 202; https://doi.org/10.3390/fluids10080202 (registering DOI) - 1 Aug 2025

Abstract

The authors would like to make the following correction to this published paper [...] Full article

16 pages, 24404 KiB

Open AccessArticle

Oxidation of HfB₂-HfO₂-SiC Ceramics Modified with Ti₂AlC Under Subsonic Dissociated Airflow

by Elizaveta P. Simonenko, Aleksey V. Chaplygin, Nikolay P. Simonenko, Ilya V. Lukomskii, Semen S. Galkin, Anton S. Lysenkov, Ilya A. Nagornov, Artem S. Mokrushin, Tatiana L. Simonenko, Anatoly F. Kolesnikov and Nikolay T. Kuznetsov

Corros. Mater. Degrad. 2025, 6(3), 35; https://doi.org/10.3390/cmd6030035 (registering DOI) - 1 Aug 2025

Abstract

Ultrahigh-temperature ceramic composites based on hafnium diboride have a wide range of applications, including as components for high-speed aircraft and energy generation and storage devices. Consequently, developing methodologies for their fabrication and studying their properties are of paramount importance, in particular in using them as an electrode material for energy storage devices with increased oxidation resistance. This study investigates the behavior of ceramic composites based on the HfB₂-HfO₂-SiC system, obtained using 15 vol% Ti₂AlC MAX-phase as a sintering component, under the influence of subsonic flow of dissociated air. It was determined that incorporating the modifying component (Ti₂AlC) altered the composition of the silicate melt formed on the surface during ceramic oxidation. This modification led to the observation of a protective antioxidant function. Consequently, liquation was observed in the silicate melt layer, resulting in the formation of spherical phase inhomogeneities in its volume with increased content of titanium, aluminum, and hafnium. It is hypothesized that the increase in the high-temperature viscosity of this melt prevents it from being carried away in the form of drops, even at a surface temperature of ~1900–2000 °C. Despite the established temperature, there is no sharp increase in its values above 2400–2500 °C. This is due to the evaporation of silicate melt from the surface. In addition, the electrochemical behavior of the obtained material in a liquid electrolyte medium (KOH, 3 mol/L) was examined, and it was shown that according to the value of electrical conductivity and specific capacitance, it is a promising electrode material for supercapacitors. Full article

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25 pages, 5020 KiB

Open AccessReview

Research Progress on Tribological Properties of High-Entropy Alloys

by Shuai Zhang, Zhaofeng Wang, Wenqing Lin and Haoyu Guo

Lubricants 2025, 13(8), 342; https://doi.org/10.3390/lubricants13080342 (registering DOI) - 1 Aug 2025

Abstract

As a new type of alloy system composed of five or more principal components, high-entropy alloys demonstrate outstanding comprehensive performance in the field of friction and wear through the synergistic effects of the high-entropy effect, lattice distortion effect, hysteresis diffusion effect and cocktail effect. This paper systematically reviews the research progress on the friction and wear properties of high-entropy alloys. The mechanisms of metal elements such as Al, Ti, Cu and Nb through solid solution strengthening, second-phase precipitation and oxide film formation were analyzed emphatically. And non-metallic elements such as C, Si, and B form and strengthen the regulation laws of their tribological properties. The influence of working conditions, such as high temperature, ocean, and hydrogen peroxide on the friction and wear behavior of high-entropy alloys by altering the wear mechanism, was discussed. The influence of test conditions such as load, sliding velocity and friction pair matching on its friction coefficient and wear rate was expounded. It is pointed out that high-entropy alloys have significant application potential in key friction components, providing reference and guidance for the further development and application of high-entropy alloys. Full article

(This article belongs to the Special Issue Tribological Performance of High-Entropy Alloys)

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16 pages, 1212 KiB

Open AccessArticle

Harnessing Mixed Fatty Acid Synergy for Selective Flotation of Apatite from Calcite and Quartz with Sodium Alginate

by Imane Aarab, Khalid El Amari, Abdelrani Yaacoubi, Abdelaziz Baçaoui and Abderahman Etahiri

Minerals 2025, 15(8), 822; https://doi.org/10.3390/min15080822 (registering DOI) - 1 Aug 2025

Abstract

Maximizing the efficient utilization of critical apatite resources through flotation necessitates the exploration of effective and innovative collectors. This study investigates the potential of a fatty acid mixture (FAM) synthesized from saturated palmitic and stearic acids, monounsaturated oleic and palmitoleic acids, and polyunsaturated linoleic acid. The saponified collector FAM and the depressant sodium alginate (NaAl) achieved a direct flotation of apatite from calcite and quartz (97% apatite, 10% calcite, and 7% quartz). The flotation performance with the tested combination exhibited a highly effective enrichment of apatite, mainly from calcite, which aligns with the surface chemistry assessments. Adsorption tests and zeta potential measurements confirmed the micro-flotation results. They provided compelling evidence of a chemisorption interaction between Ca²⁺ sites on calcite and the carboxyl and hydroxyl groups of NaAl. FTIR analyses suggested a reaction between the apatite surface and the carboxyl groups of saturated and unsaturated acid groups in FAM, even those conditioned with NaAl before, facilitating the complex formation. Remarkably, the synergistic effect of the functional groups demonstrates dual functionality, serving as both a hydrophilic entity for calcite and a hydrophobic entity for apatite flotation. The universal mechanism unveils substantial potential for the extensive application of FAM within apatite flotation. Full article

(This article belongs to the Special Issue Surface Chemistry and Reagents in Flotation)

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