Immersion Conditions Research Articles

Optimization of Desalting Conditions for the Green Seaweed Codium fragile for Use as a Functional Food with Hypnotic Effects.

Codium fragile (CF) contains various bioactive compounds, but its high salt content (39.8%) makes its use as a functional food challenging. Here, we aimed to optimize the desalination process and verify changes in functionality based on variations in salt and total phenolic contents. To optimize the CF immersion conditions for the lowest salt content and monitor the total phenolic content, a response surface methodology was used. The optimal immersion conditions were as follows: X1 (immersion temperature) = 42.8 °C; X2 (immersion time) = 1.0 h. An inverse correlation was noted between salt content and total phenolic content. Among the post-desalination processes, desalination with centrifugal dehydration (CD) significantly reduced salt content. CD ethanol extract (CD-E) induced the longest sleep duration in the pentobarbital-induced sleep test in ethanol extracts. Moreover, 1000 mg/kg CD-E had a significant effect on non-rapid eye movement sleep but did not affect delta activity. These findings highlight the potential of industrializing CF as a functional food through desalination and its promise as a natural aid for sleep promotion.

The Field Assessment of Quiescent Egg Populations of Aedes aegypti and Aedes albopictus during the Dry Season in Tapachula, Chiapas, Mexico, and Its Potential Impact on Vector Control Strategies.

Although integrated management and control programs implement intense control measures for adult, pupal, larval, and breeding sites during outbreaks, there is a lack of studies to understand the role of the vector egg stage in disease dynamics. This study aimed to assess the dry season quiescent Aedes aegypti and Aedes albopictus egg populations in houses and backyards in Tapachula, southern Mexico. Two hundred and fifty ovitraps were placed in 125 homes in the Las Americas neighborhood. A total of 7290 eggs were collected from 211 (84.4%) ovitraps. Only 5667 (77.7%) hatched under insectary water immersion and food supply conditions, with 4031 (71.1%) identified as Ae. aegypti, and 1636 (28.8%) as Ae. albopictus, respectively. The remaining 1623 (22.3%) did not hatch due to Delayed Hatching and/or quiescence tropical stage. Eighty-three larval containers were sampled with desiccated eggs during the dry season; most of them were described as trash waste because larvicides are only used for larger containers of 5-10 L. Evolutionary characteristics for the two species including partial egg hatching, ambient-regulated quiescence, the ability of the embryo to survive for a more extended period intra-seasonally, the egg sticking to inner container walls, demands urgent operational research to achieve successful egg-proof larval container methods.

Enhancing durability and oil-water separation efficiency with plasma-treated graphene oxide coated mesh

In recent years, there has been a surge in interest surrounding the fabrication and utilization of superhydrophobic and superhydrophilic surfaces, driven by their exceptional functionalities and properties. Graphene Oxide (GO) has inherent hydrophilicity and underwater superoleophobicity, which has made this material a particularly capable candidate for oil-water separation. Addressing the persistent challenge of efficient oil-water separation in industrial contexts, this study presents the fabrication of a GO-coated stainless steel mesh via a facile dip coating method augmented by an intermediate two-step O2 plasma treatment. The coated meshes were tested with various oil and water mixtures, including neutral, acidic, saline, and hot water, to find separation efficiency and recyclability. Notably, the meshes can achieve excellent separation efficiency of approximately 98.9 % and a superior flux of 11,464 L m−2 h−1 driven by gravity. This is a significant improvement over GO-coated meshes without O2 plasma treatment. Moreover, the plasma-treated meshes exhibit robust long-term durability and chemical stability, maintaining high underwater oil contact angles ≥119° even after extended immersion in diverse pH mediums and salt solutions for 150 days. This work showcases the practical viability of plasma-treated GO-coated meshes for oil-water separation applications and establishes a framework for systematically evaluating their long-term performance in harsh immersion conditions.

A novel energy-saving and emission-reduction strategy based on facile preparation of thermal insulation coatings doped with modified vacuum ceramic microbeads for concrete protection

The development of thermal insulation protective coatings suitable for constructions and buildings offers a multifaceted approach: it substantially reduces indoor temperatures, enhances residential comfort, decreases air conditioning energy consumption, and conserves energy. Additionally, these coatings provide robust resistance against corrosive substances, thereby significantly prolonging the service life of concrete. In this work, the modification of vacuum ceramic microbeads (VCM) through the polymerization of catechol and hexamethylene diamine to form poly(catecholamine) (PCA) was investigated by FT-IR, XRD, and TEM analysis. Increased levels of incorporation of VCM@PCA further decreased thermal conductivity and increased surface hydrophobicity, while excessive incorporation detrimentally affected the coating's mechanical properties. PDMS/VCM@PCA coating demonstrated exceptional thermal insulation performance, reducing coating temperature by 15.9 °C under simulated sunlight exposure, and in outdoor experiments, the interior temperature of the simulated house with this coating was 4.2 °C lower than the external temperature, highlighting its potential for energy conservation, emission reduction, and building temperature regulation. Additionally, PDMS/VCM@PCA coating provided excellent protection for concrete structures, significantly enhancing abrasion resistance. It also improved the interfacial adhesion between the organic layer and concrete under dry, wet, and 10% NaCl immersion conditions. The addition of VCM@PCA further enhanced resistance to chloride ion penetration, effectively reducing chloride ingress. This thermal insulation protective coating presents a novel strategy for energy conservation, emission reduction, and sustainable development in the civil construction industry.

Metacognitive Awareness in Second Language Learning: Displaced Primary School Students’ Experiences of Learning German Upon Transition to the Target Language Environment

Drawing on international pedagogical discourse on the inclusion of ethnically diverse refugee groups in the educational systems of OECD countries as well as our previous research on the Ukrainian refugee perspectives on primary school in Switzerland, the author examines experiences of second language acquisition by displaced Ukrainian children in Swiss primary schools. The two-year research period allowed for the exploration of dynamics of German language acquisition by displaced children in conditions of full immersion in the target language environment and identification of the factors influencing their second language (German) learning and performance. The involvement of a Ukrainian researcher in the research project ensured accessibility of the target group and effective researcher-respondent communication in the course of longitudinal study carried out within the framework of a qualitative methodology with data collection through narrative inquiry and participant observations as research tools. The study identifies the effects of the two groups of factors: learner-internal (motivation, metacognitive skills, prior knowledge, and learning strategies) and learner-external ones (second language learning context, type of second language instruction available upon displacement, etc.). Metacognitive skills proved to be instrumental in second language learning in the context of the learners’ unexpected transition to a new educational setting and full immersion in the target language environment. Effects of metacognitive skills on second language learning of the studied group of displaced children vary considerably depending on the student’s age, prior knowledge and language learning experiences, and second language instruction available upon the displacement. The multidisciplinary character of the second language acquisition research undertaken by the author allows for diverse practical applications of its results in second language pedagogy, psychology of education, as well as in refugee and primary education.

Natural- and redirected walking in virtual reality: Spatial performance and user experience

AbstractImmersive virtual reality offers a range of unique possibilities. One of these is the realistic exploration of virtual worlds using natural walking. This however becomes difficult when the size of the virtual world exceeds that of the available physical space. Redirected walking in virtual reality presents a novel solution to this problem by typically making its users think to be walking in a straight line while they are in fact walking in a curve, thus allowing them to physically walk long distances in confined physical spaces. Yet, few studies have examined the effects of redirected walking on variables such as spatial memory, navigation and user experience as compared to other immersive and non-immersive locomotion methods. In a maze task we examined 1) redirected- and 2) natural walking in immersive virtual reality conditions, and 3) artificial locomotion on a non-immersive desktop monitor. Walked path lengths became shorter and distance estimates, object location memory and user experience improved using natural walking compared to a monitor condition. However, redirected walking yielded similar performance to natural walking while requiring less physical space, opening up possibilities for more pervasive use of real locomotion in virtual environments.

Attenuation Law of Performance of Concrete Anti-Corrosion Coating under Long-Term Salt Corrosion

In saline soil areas, the concrete piers of concrete bridges experience long-term corrosion, mainly caused by chloride salts due to alternating temperature changes. Waterborne concrete coatings are prone to failure in this aggressive salt environment. Implementing coating protection measures can improve the durability of concrete and enhance the service life of bridges. However, the effectiveness and longevity of coatings need further research. In this paper, three types of waterborne concrete anti-corrosion coatings were applied to analyze the macro and micro surface morphology under wet–dry cycles and long-term immersion conditions. Various indicators such as glossiness, color difference, and adhesion of the coatings were tested during different cyclic periods. The chloride ion distribution characteristics of the buried concrete coatings in saline soil, the macro morphology analysis of chloride ion distribution regions, and the micro morphology changes of the coatings under different corrosion times were also investigated. The results showed that waterborne epoxy coatings (ES), waterborne fluorocarbon coatings (FS), and waterborne acrylic coatings (AS) all gradually failed under long-term salt exposure, with increasing coating porosity, loss of internal fillers, and delamination. The chloride ion content inside the concrete decreased with increasing depth at the same corrosion time, while the chloride ion content at the same depth increased with time. The chloride ion distribution boundary in the cross-section of concrete with coating protection was not significant, while the chloride ion distribution boundary in the cross-section of untreated concrete gradually contracted towards the concrete core with increasing corrosion time. During the corrosion process in saline soil, the coatings underwent three stages: adherence of small saline soil particles, continuous increase in adhered material area, and multiple layers of uneven coverage by saline soil. The failure process of the coatings still required erosive ions to infiltrate the surface through micropores. The predicted lifespans of FS, ES, and AS coatings, obtained through weighted methods, were 2.45 years, 2.48 years, and 2.74 years, respectively, which were close to the actual lifespans observed in salt environments. The developed formulas effectively reflect the corrosion patterns of different resin-based coatings under salt exposure, providing a basis for accurately assessing the corrosion behavior and protective effectiveness of concrete under actual environmental factors.

Direct Measurement of the Diffusion Coefficient of Adhesives from Moisture Distribution in Adhesive Layers Using Near-Infrared Spectroscopy.

In this study, we used near-infrared spectroscopy to measure the moisture penetration in epoxy adhesives and investigated the difference in the diffusion coefficients between the bulk and the adhesive layer. Moisture diffusion was evaluated under 100% RH and water immersion conditions. First, the effects of the curing agents and additives on moisture diffusion in the bulk were gravimetrically evaluated using epoxy-coated quartz glass plates. Different diffusion behaviors were observed depending on the curing agent used. The presence of additives resulted in higher diffusion coefficients, whereas the overall moisture content was low. Next, the moisture distribution in the adhesive layer was visualized using a specimen sandwiched between the quartz glass plates, and the diffusion coefficient of the adhesive layer was calculated. The diffusion coefficient in the adhesive layer was larger than that in the bulk. For adhesives cured with hydrophobic diamine, the diffusion coefficient within the adhesive layer increased by approximately 1.5 times compared with that in the bulk, regardless of the exposure environment. The adhesive, composed of a resin, Dicyandiamide, and additives, showed a 2-fold increase in the diffusion coefficient under high-humidity exposure conditions but no significant change under the water immersion condition. Therefore, these results suggest that, for an accurate analysis of moisture distribution, it is important to measure the diffusion coefficient of the adhesive layer directly rather than using the diffusion coefficient of the material itself.

In Situ Fabrication of Highly Efficient and Stable Cs2NaInCl6: Sb3+@PVDF Composite Films for Optoelectronic Devices.

Lead-free double perovskites (DPs) have superior phase stability and optical properties, which make them competitive for future applications in illumination and displays. However, the preparation of DPs was mainly based on high-temperature heating and hydrochloric acid as a solvent to form powders, which increased the risk and cost of the preparation process and limited its further application. In this study, the growth of Cs2NaInCl6: Sb3+ DPs in polyvinylidene difluoride (PVDF) films was achieved using an in situ fabrication strategy with DMSO as the solvent. The prepared Cs2NaInCl6: Sb3+@PVDF composite films (CFs) can achieve a bright blue emission under 302 nm irradiation. To achieve the optimal luminescent performance of CFs, the photoluminescence (PL) intensity of Cs2NaInCl6: Sb3+@PVDF CFs under various in situ preparation conditions was compared. In addition, the photoluminescence quantum yield (PLQY) of CFs was increased from 0.72% to 83.77% by adjusting the doping amount of Sb3+, and the fluorescence lifetimes t1 and t2 were 131.08 and 1048.52 ns, respectively. Temperature-dependent PL spectroscopy and density functional theory (DFT) calculations indicate that these excellent optical properties are derived from the self-trapped excitons (STEs) at the [SbCl6]3- octahedron and [InCl6]3- octahedron connected via Cl-Na-Cl. The CFs also demonstrated excellent environmental stability, maintaining a relatively stable PL intensity even under conditions of water immersion, high temperatures, and ultraviolet (UV) radiation. Finally, we used the CFs to assemble a blue light-emitting device (LED), which showed good and stable blue emission performance at different currents. This work can provide a new idea for preparing DPs, which is conducive to promoting their commercial application in high-performance optoelectronic devices.

Augmenting home entertainment with digitally delivered touch.

In this narrative review, we take a critical look at the various attempts that have been made to augment home (or personal) entertainment experiences via the addition of some form of digitally controlled tactile stimulation. There has been an explosive growth in the market for home entertainment in recent years, and a majority of smartphones and other wearable electronic devices are now touch-enabled. As such, it is important to consider the challenges and potential opportunities for enhanced multisensory entertainment that may result from the introduction of tactile/haptic stimulation in the context of audiovisual digital storytelling and/or gaming. The key technological, financial (and legal), cognitive, and creative/artistic, challenges associated with the tactile augmentation of home entertainment experiences are outlined. Tactile augmentation, in the sphere of both public and personal entertainment, is more likely to succeed when it goes beyond the merely pleonastic vibrotactile reproduction of those interactions/events than can already be seen and/or heard on screen. At the same time, however, it remains uncertain under what conditions immersion in an entertainment experience will be enhanced by the addition of some form of primitive digital tactile stimulation. Ultimately, until a clear usage case can be made for the benefits of introducing a tactile element to home entertainment, it is unlikely to gain traction and switch from being merely a gimmick to more of a valuable element of multisensory storytelling.

Flexural behavior of coral aggregate concrete beams reinforced with BFRP bars under seawater corrosion environments

The combined utilization of fiber-reinforced polymer (FRP) composites with coral aggregate concrete (CAC) in remote island areas contributes to the reduced construction cost and construction period, offering a promising application. However, the evolution pattern and deterioration mechanism of flexural behavior for FRP bars reinforced CAC beams in marine service environments remains unclear. Thus, this paper investigates the flexural behavior of basalt-FRP (BFRP) bars reinforced CAC beams under seawater immersion and dry-wet cycle conditions using laboratory-accelerated aging methods. The research considers the effects of exposure temperature and corrosion age on their failure modes, flexural stiffness, ultimate loading capacity, and deformation deflection. The experimental results revealed that with the increase in corrosion age and exposure temperature, the amount of vertical cracks of CAC beams decreased and their crack depth also exhibited a slight reduction, but their crack width and spacing at failure significantly increased. After being attacked by seawater environments, the load-deflection curves of CAC beams experienced an enhanced slope of the ascending section (i.e., flexural stiffness), but this strengthened flexural stiffness did not result in an enhancement in the ultimate load capacity. Instead, with prolonged corrosion and higher temperatures, the ultimate load of CAC beams displayed significant degradation, accompanied by reduced mid-span deflection. After 12 months of seawater exposure to wet-dry cycle conditions at 60 °C, the ultimate load and mid-span deflection of CAC beams degraded by approximately 25.0 % and 56.6 %, respectively. The study also predicted the flexural bearing capacity of CAC beams utilizing existing specifications for FRP-reinforced normal aggregate concrete (NAC). It was concluded that the formulae for flexural loading capacity for FRP-reinforced NAC beams were still suitable for CAC beams.

Enhancing adhesive interlayer performance with waste tire rubber and amorphous poly alpha olefin compound modified asphalt

Insufficient bonding performance in interlayers is a key factor in the deterioration of bridge deck pavements. This study evaluates the bonding and durability of Waste Tire Rubber (WTR)/Amorphous Poly Alpha Olefin (APAO) modified asphalt compared to the commonly used Styrene-Butadiene-Styrene (SBS) modified asphalt. We conducted shear and pull tests to analyze how different bonding processes and the texture depth of the concrete surface affect bonding performance. The research also assessed the durability of the adhesive layer under conditions such as temperature fluctuations, water immersion, and aging. Results show that the choice of bonding method significantly impacts adhesive performance, with the coating bond method being superior to the crushed stone bond method. A concrete surface texture depth of 0.88 mm was identified as optimal for improving adhesive performance. Moreover, the WTR/APAO adhesive interlayer provided better adhesive and durability performance than the SBS adhesive interlayer under conditions of temperature fluctuations and water immersion. Based on these findings, the study recommends using the coating bond process and 15%WTR + 4%APAO modified asphalt for the adhesive interlayer.

Immersive and Nonimmersive Virtual Reality-Assisted Active Training in Chronic Musculoskeletal Pain: Systematic Review and Meta-Analysis.

Virtual reality (VR) in different immersive conditions has been increasingly used as a nonpharmacological method for managing chronic musculoskeletal pain. We aimed to assess the effectiveness of VR-assisted active training versus conventional exercise or physiotherapy in chronic musculoskeletal pain and to analyze the effects of immersive versus nonimmersive VR on pain outcomes. This systematic review of randomized control trials (RCTs) searched PubMed, Scopus, and Web of Science databases from inception to June 9, 2024. RCTs comparing adults with chronic musculoskeletal pain receiving VR-assisted training were included. The primary outcome was pain intensity; secondary outcomes included functional disability and kinesiophobia. Available data were pooled in a meta-analysis. Studies were graded using the Cochrane Risk-of-Bias Tool version 2. In total, 28 RCTs including 1114 participants with some concerns for a high risk of bias were identified, and 25 RCTs were included in the meta-analysis. In low back pain, short-term outcomes measured post intervention showed that nonimmersive VR is effective in reducing pain (standardized mean difference [SMD] -1.79, 95% CI -2.72 to -0.87; P<.001), improving disability (SMD -0.44, 95% CI -0.72 to -0.16; P=.002), and kinesiophobia (SMD -2.94, 95% CI -5.20 to -0.68; P=.01). Intermediate-term outcomes measured at 6 months also showed that nonimmersive VR is effective in reducing pain (SMD -8.15, 95% CI -15.29 to -1.01; P=.03), and kinesiophobia (SMD -4.28, 95% CI -8.12 to -0.44; P=.03) compared to conventional active training. For neck pain, immersive VR reduced pain intensity (SMD -0.55, 95% CI -1.02 to -0.08; P=.02) but not disability and kinesiophobia in the short term. No statistical significances were detected for knee pain or other pain regions at all time points. In addition, 2 (8%) studies had a high risk of bias. Both nonimmersive and immersive VR-assisted active training is effective in reducing back and neck pain symptoms. Our study findings suggest that VR is effective in alleviating chronic musculoskeletal pain. PROSPERO CRD42022302912; https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=302912.

How immersive technologies impact behavioral responses in destination marketing: the role of physiological arousal, presence, and age

PurposeThis paper aims to investigate the effectiveness of immersive virtual reality (VR) media and the influence of user’s age in the context of destination marketing by exploring their impact on cognition (presence), affection (arousal), and behavioral (intention to visit and intention to recommend the destination) outcomes.Design/methodology/approachA laboratory experiment was conducted to compare the impact of using immersive VR (vs. 2D desktop) to experience a 360-degree virtual tour of Valencia on consumers’ behavior. The sample included 187 participants. Both self-reported and physiological measures were collected during the experimentation.FindingsResults showed that participants in the immersive condition experienced a stronger sense of presence and higher physiological arousal than those exposed to nonimmersive content. Presence significantly mediated both the intention to visit and the intention to recommend the promoted venue. Physiological arousal mediated the relationship between media typology and the intention to recommend the destination. Upon introducing age as a moderating variable, the effect of physiological arousal on behavioral outcomes proves to be significant.Practical implicationsThe study presents destination marketing organizations with a compelling use case for immersive technologies. It also offers design principles, potential applications and targeting strategies for VR marketing in hospitality management.Originality/valueTo the best of the authors’ knowledge, this study is the first to investigate the combined effect of physiological arousal and presence on behavioral intentions in VR destination marketing, while also examining the impact of age as an individual characteristic.

Research on the evolution law of aggregate micro-texture during long-term wearing of asphalt pavement

The micro-texture of aggregates plays a very important role in anti-skid performance of asphalt pavement. Three kinds of aggregates, limestone, basalt and sandstone, were used to prepare asphalt mixture to study the evolution law of micro-texture of aggregates under long-term wear. One Third Scaled Model Mobile Load Simulator (MMLS) was used to conduct wear tests on asphalt mixtures under two working conditions: drying and water immersion. Laser confocal scanning microscopy (LCSM) was used to test and analyze the micro-texture evolution of the original aggregate, mixed aggregate, and accelerated loaded aggregate surfaces. The mechanism of texture evolution was analyzed based on the mineral composition, Vickers hardness, and micro-structure of the aggregate. The results show that wear can lead to varying degrees of polishing of the aggregate micro-texture, with limestone>basalt>sandstone, and the drying condition is more severe than the water immersion condition. The wear degree of the texture is closely related to the mineral composition and hardness of the aggregate. The more complex the mineral composition, the greater the hardness and hardness dispersion, the less likely the texture will be polished. The micro-texture indexes Ra and Rq have the highest correlation with anti-skid performance, and the relationship between them is obtained by fitting. Scanning electron microscopy (SEM) shows that the fine particles in sandstone are easy to fall off, which is conducive to the regeneration of texture, and is also the internal reason for its best anti-skid durability.

Phased array-based nonlinear wave mixing technique: Application to lack-of-fusion porosity characterization in additively manufactured metals.

The objective of this research is to demonstrate the effectiveness of a phased array-based nonlinear wave mixing technique to characterize internal, localized microscale damage in an additively manufactured (AM) component. By using phased arrays for the generation of the incident waves, it is possible to produce a nonlinear wave mixing scanning technique without the need for immersion or changing coupling conditions. The phased arrays can be configured to generate incident waves in multiple directions that meet the resonance conditions required for nonlinear wave mixing at a variety of internal locations. This allows for the scanning of a specimen without the removal and re-coupling of the source transducers, leading to greater scanning speed and repeatability. To demonstrate the accuracy of this phased array wave mixing approach, measurements of acoustic nonlinearity in an AM component are first made with a bulk wave second harmonic generation through thickness measurement. Next, nonlinear wave mixing measurements are made with single element transducers to confirm the sensitivity of the proposed nonlinear wave mixing approach to lack-of-fusion porosity in AM metals. Finally, phased arrays are used to highlight the effectiveness of the proposed nonlinear wave mixing technique in these same AM components.

Modification on Fiber from Alkali Treatment and AESO Coating to Enhance UV-Light and Water Absorption Resistance in Kapok Fiber Reinforced Polyester Composites

ABSTRACT Environmental contamination poses a significant threat to the integrity of materials, including metals and composites. Addressing the degradation of natural fiber-reinforced polymer composites necessitates effective management strategies, particularly in mitigating UV and water-induced deterioration. This study explores the efficacy of Acrylated Epoxidized Soybean Oil (AESO) coating treatment following alkali treatment as a potential solution. Alkali treatment of Kapok fiber (KF) combined with polymer coating yielded composites exhibiting superior mechanical properties, particularly in tensile and flexural strength, following a 30-day aging period. Remarkably, the application of alkali and coating treatments led to a substantial enhancement in the mechanical strength of polyester composites, with the highest tensile strength recorded at 96.04 MPa. This represented a notable increase of 31.97% compared to untreated KF specimens. The observed enhancement in composite performance underscores the critical role of interfacial adhesion between fibers and the matrix, particularly under conditions of UV exposure and water immersion. Importantly, the study demonstrates that alkali treatment and polymer coating effectively mitigate degradation in Natural Fiber-Reinforced Polymer Composites, thereby offering promising avenues for enhancing their durability and longevity.

Acute Effects of Breath-Hold Conditions on Aerobic Fitness in Elite Rugby Players.

The effects of face immersion and concurrent exercise on the diving reflex evoked by breath-hold (BH) differ, yet little is known about the combined effects of different BH conditions on aerobic fitness in elite athletes. This study aimed to assess the acute effects of various BH conditions on 18 male elite rugby players (age: 23.5 ± 1.8 years; height: 183.3 ± 3.4 cm; body mass: 84.8 ± 8.5 kg) and identify the BH condition eliciting the greatest aerobic fitness activation. Participants underwent five warm-up conditions: baseline regular breathing, dynamic dry BH (DD), static dry BH (SD), wet dynamic BH (WD), and wet static BH (WS). Significant differences (p < 0.05) were found in red blood cells (RBCs), red blood cell volume (RGB), and hematocrit (HCT) pre- and post-warm-up. Peak oxygen uptake (VO2peak) and relative oxygen uptake (VO2/kgpeak) varied significantly across conditions, with BH groups showing notably higher values than the regular breathing group (p < 0.05). Interaction effects of facial immersion and movement conditions were significant for VO2peak, VO2/kgpeak, and the cardiopulmonary optimal point (p < 0.05). Specifically, VO2peak and peak stroke volume (SVpeak) were significantly higher in the DD group compared to that in other conditions. Increases in VO2peak were strongly correlated with changes in RBCs and HCT induced by DD warm-up (r∆RBC = 0.84, r∆HCT = 0.77, p < 0.01). In conclusion, DD BH warm-up appears to optimize subsequent aerobic performance in elite athletes.

Effect of hygrothermal aging on the friction behavior and wear mechanism of the multi-filler reinforced epoxy composites for coated steel

Polymer-based composites for steel structure coating are an effective strategy to improve tribological properties and service durability under hygrothermal aging conditions. In the present paper, epoxy resin was improved by mechanical reinforcement and frictional lubrication fillers, and a kind of multi-filler reinforced epoxy composite (MFREC) was successfully prepared. Water uptake behavior, mechanical and thermal property evolution, friction behavior and wear mechanism as well as micro-topography analysis of MFREC under hygrothermal aging were conducted and discussed in detail. The research results showed that the water uptake curve of MFREC after distilled water and 5 wt% NaCl water solution immersions confirmed the two-stage diffusion model, where the quasi-equilibrium water uptakes were 4.23% and 3.67%, respectively. Additionally, the fundamental reason for the degradation of the mechanical and thermal properties of MFREC was the hydrolysis of the resin and the de-bonding of the fillers/matrix interface. The interface shear strength of MFREC adhesive and steel gradually decreased with the hygrothermal aging, but did not lose the bonding property, because the uniformly dispersed multi-fillers can fill the internal defects of the matrix and prolong the crack propagation path to block the effect. Before hygrothermal aging, MFREC had excellent friction and wear resistance compared to resin matrix, especially under water lubrication conditions. The anti-wear rate of MFREC increased by up to 59.6% compared to the room temperature dry test environment due to the coupling effects of the water lubrication and anti-friction characteristics of modified fillers. Hygrothermal aging had little effect (＜12%) on the friction coefficient of MFREC, but the anti-wear properties decreased significantly, especially the Ws increased by 255.1% under the 60 °C immersion condition. Because the degradation of thermal/mechanical properties was not enough to resist the high shear stress of the steel ball, leading to severe fatigue wear.

Tribological behaviors and wettability evolution of phenolic resin-impregnated graphite materials under water immersion condition

This study investigated the tribological behaviors of two phenolic resin-impregnated graphite samples and one non-impregnated sample under dry and water immersion using a reciprocating testing device. The frictional configuration involved a steel hemisphere sliding against the surface of the graphite samples. The influence of water immersion time before each formal test on friction coefficients was discussed. The wettability evolution during the test processes and the difference in porosity, which could significantly affect water infiltrating into the sample matrix and frictional interfaces, were associated with the variation in tribological behaviors. The worn surface morphology and element analysis results indicated that the shallow valleys and pores on the surface of graphite were gradually filled by wear debris from both the graphite samples and the harder counterpart. Based on these experimental results, a tribological mechanism of the phenolic resin-impregnated graphite materials under water immersion was developed.