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Vitrimers, although categorized as thermosetting polymers, differ from traditional ones in that their thermally induced crosslinks undergo reconfiguration through covalent bond exchanges in response to thermal stimuli. Exchangeable bonds present significant and distinctive advantages for thermoset‐based aerospace composites, facilitating capabilities such as self‐repair and crack arrest through molecular bridging. In this work, the self‐healing behavior of four different blends of Aromatic Thermosetting Copolyester (ATSP) coatings, which are high‐performance vitrimer polymers, is tested by introducing micro‐scratches on the surface and healing them at higher temperatures. In three blends, the scratches are completely healed indicating complete repair. This property of the ATSP coatings can be useful in extreme conditions where micro‐cracks lead to failure. The healing ability of the vitrimers is discussed in terms of their mechanical properties and morphological parameters such as branch density.

Some tribological applications demand reliable operation over a wide range of temperatures and the absence of liquid lubrication. Under these circumstances, polymer composite coatings have been suggested as an alternative to liquid lubrication. This study investigates the tribological performance of an advanced high-bearing aromatic thermosetting polyester (ATSP) coating filled with well-known solid lubricants, namely polytetrafluoroethylene (PTFE) and graphene nanoplatelets (GNPs). Mechanical and thermo-mechanical properties of the coatings were measured using nanoindentation and dynamic mechanical analysis. The tribological performance was experimentally assessed using a flat pin-on-disk configuration from room temperature to 300 °C with dry sliding conditions. The results showed that the addition of GNPs and PTFE could significantly decrease the friction and improve the wear resistance of the composite coatings, compared to neat ATSP coating. Both composite coatings demonstrated enhanced tribological performance with the increase of temperature. However, at the most extreme condition of 300 °C, the GNPs outperformed the PTFE by reducing the friction and wear by 53% and 69%, respectively, compared to room temperature. Optical and scanning electron microscopy were employed to further examine the formation of transfer films and worn surfaces.

Political institutions may directly affect the likelihood of currency crises by influencing market confidence. They may indirectly affect the likelihood of currency crises by influencing economic fundamentals. This study uses econometric mediation to estimate both direct and indirect causal pathways for veto player theory—a common framework for analyzing political institutional constraints—and finds this approach improves upon the standard econometric approach in the extant literature, which only estimates the direct causal pathway. This new mediated approach shows that political constraints also indirectly reduce the likelihood of crises through strengthening key economic fundamentals. Additionally, the analysis finds that when global conditions are stable, more constraints are shown to directly reduce the risk of crises. When global conditions are volatile, more constraints are shown to directly increase the risk of crises. Global volatility is more likely to cause crises in countries with relatively constrained political systems, and vice versa.

Monitoring of surface waters in the boreal region over the last decades shows that waters are becoming browner. This timeframe may not, however, be sufficient to capture underlying trajectories and driving mechanisms of lake-water quality, important for prediction of future trajectories. Here we synthesize data from seven lakes in the Swedish boreal landscape, with contemporary lake-water total organic carbon (TOC) concentrations of 1.4–14.4 mg L−1, to conceptualize how natural and particularly human-driven processes at the landscape scale have regulated lake-water TOC levels over the Holocene. Sediment-inferred trends in TOC are supported by several proxies, including diatom-inferred pH. Before ∼ 700 CE, all lakes were naturally acidic (pH 4.7–5.4) and the concentrations of inferred lake-water TOC were high (10–23 mg L−1). The introduction of traditional human land use from ∼ 700 CE led to a decrease in lake-water TOC in all lakes (to 5–14 mg L−1), and in four poorly buffered lakes, also to an increase in pH by > 1 unit. During the 20th century, industrial acid deposition was superimposed on centuries of land use, which resulted in unprecedentedly low lake-water TOC in all lakes (3–11 mg L−1) and severely reduced pH in the four poorly buffered lakes. The other lakes resisted pH changes, likely due to close connections to peatlands. Our results indicate that an important part of the recent browning of boreal lakes is a recovery from human impacts. Furthermore, on a conceptual level we stress that contemporary environmental changes occur within the context of past, long-term disturbances.

ObjectiveTo investigate the levels and correlates of physical activity during COVID-19 social distancing in a sample of the UK public.MethodsThis paper presents analyses of data from a cross-sectional study. Levels of physical activity during COVID-19 social distancing were self-reported. Participants also reported on sociodemographic and clinical data. The association between several factors and physical activity was studied using regression models.ResultsNine hundred and eleven adults were included (64.0% were women and 50.4% of the participants were aged 35–64 years). 75.0% of the participants met the physical activity guidelines during social distancing. Meeting these guidelines during social distancing was significantly associated with sex (reference: male; female: OR=1.60, 95% CI 1.10 to 2.33), age (reference: 18–34 years; ≥65 years: OR=4.11, 95% CI 2.01 to 8.92), annual household income (reference: <£15 000; £15 000–<£25 000: OR=2.03, 95% CI 1.11 to 3.76; £25 000–<£40 000: OR=3.16, 95% CI 1.68 to 6.04; £40 000–<£60 000: OR=2.27, 95% CI 1.19 to 4.34; ≥£60 000: OR=2.11, 95% CI 1.09 to 4.09), level of physical activity per day when not observing social distancing (OR=1.00 (per 1 min increase), 95% CI 1.00 to 1.01), and any physical symptom experienced during social distancing (reference: no; yes: OR=0.31, 95% CI 0.21 to 0.46).ConclusionDuring COVID-19, social distancing interventions should focus on increasing physical activity levels among younger adults, men and those with low annual household income. It should be noted in the present sample that women and younger adults are over-represented.

Significance Monitoring programs have recorded increases in organic carbon concentrations in northern lakes, which have important implications for water quality and ecosystem functioning. Current hypotheses interpret this trend in light of recent environmental changes such as acidification and climate but do not include an examination of long-term changes and their causes. We inferred past trends from sediment archives across central Sweden, allowing us to assess recent changes on a millennial scale. Our data demonstrate that a long-term decline beginning already in the 15th century preceded the recent organic carbon increase. This was a response to spatially extensive human–landscape interactions that included forest grazing and mire exploitation, which were common across Europe and altered carbon cycling between terrestrial and aquatic ecosystems. Organic carbon concentrations have increased in surface waters across parts of Europe and North America during the past decades, but the main drivers causing this phenomenon are still debated. A lack of observations beyond the last few decades inhibits a better mechanistic understanding of this process and thus a reliable prediction of future changes. Here we present past lake-water organic carbon trends inferred from sediment records across central Sweden that allow us to assess the observed increase on a centennial to millennial time scale. Our data show the recent increase in lake-water carbon but also that this increase was preceded by a landscape-wide, long-term decrease beginning already A.D. 1450–1600. Geochemical and biological proxies reveal that these dynamics coincided with an intensification of human catchment disturbance that decreased over the past century. Catchment disturbance was driven by the expansion and later cessation of widespread summer forest grazing and farming across central Scandinavia. Our findings demonstrate that early land use strongly affected past organic carbon dynamics and suggest that the influence of historical landscape utilization on contemporary changes in lake-water carbon levels has thus far been underestimated. We propose that past changes in land use are also a strong contributing factor in ongoing organic carbon trends in other regions that underwent similar comprehensive changes due to early cultivation and grazing over centuries to millennia.

Understanding the evolution of Arctic polar climate from the protracted warmth of the middle Pliocene into the earliest glacial cycles in the Northern Hemisphere has been hindered by the lack of continuous, highly resolved Arctic time series. Evidence from Lake El'gygytgyn, in northeast (NE) Arctic Russia, shows that 3.6 to 3.4 million years ago, summer temperatures were ~8°C warmer than today, when the partial pressure of CO₂ was ~400 parts per million. Multiproxy evidence suggests extreme warmth and polar amplification during the middle Pliocene, sudden stepped cooling events during the Pliocene-Pleistocene transition, and warmer than present Arctic summers until ~2.2 million years ago, after the onset of Northern Hemispheric glaciation. Our data are consistent with sea-level records and other proxies indicating that Arctic cooling was insufficient to support large-scale ice sheets until the early Pleistocene.

Dielectric elastomers (DE) are novel composite architectures capable of large actuation strains and the ability to be formed into a variety of actuator configurations. However, the high voltage requirement of DE actuators limits their applications for a variety of applications. Fiber actuators composed of DE fibers are particularly attractive as they can be formed into artificial muscle architectures. The interest in manufacturing micro or nanoscale DE fibers is increasing due to the possible applications in tissue engineering, filtration, drug delivery, catalysis, protective textiles, and sensors. Drawing, self-assembly, template-direct synthesis, and electrospinning processing have been explored to manufacture these fibers. Electrospinning has been proposed because of its ability to produce sub-mm diameter size fibers. In this paper, we investigate the impact of electrospinning parameters on the production of composite dielectric elastomer fibers. In an electrospinning setup, an electrostatic field is applied to a viscous polymer solution at an electrode’s tip. The polymer composite with carbon black and carbon nanotubes is expelled and accelerated towards a collector. Factors that are considered in this study include polymer concentration, solution viscosity, flow rate, electric field intensity, and the distance to the collector.

Development of porous materials consisting of polymer host matrix enriched with bioactive ceramic particles that can initiate the reproduction of cellular organisms while maintaining in vivo mechanical reliability is a long-standing challenge for synthetic bone substitutes. We present hydroxyapatite (HA) reinforced aromatic thermosetting copolyester (ATSP) matrix bionanocomposite as a potential reconfigurable bone replacement material. The nanocomposite is fabricated by solid-state mixing a matching set of precursor oligomers with biocompatible pristine HA particles. During endothermic condensation polymerization reaction, the constituent oligomers form a mechanochemically robust crosslinked aromatic backbone while incorporating the HAs into a self-generated cellular structure. The morphological analysis demonstrates near-homogenous distributions of the pristine HAs within the matrix. The HAs behave as a crack-arrester which promotes a more deformation-tolerant formation with relatively enhanced material toughness. Chain relaxation dynamics of the nanocomposite matrix during glass transition is modified via HA-induced segmental immobilization. Chemical characterization of the polymer backbone composition reveals the presence of a hydrogen-advanced covalent interfacial coupling mechanism between the HAs and ATSP matrix. This report lays the groundwork for further studies on aromatic thermosetting copolyester matrix bionanocomposites which may find applications in various artificial bone needs.

Background Sedentary time (SED) is associated with many detrimental health outcomes, yet little is known about what factors influence one’s ability to reduce SED. Even less is known about these factors in specific patient populations for whom high levels of SED may influence symptoms, such as those with chronic low back pain (cLBP). The purpose of this study was to qualitatively explore participants’ perceptions of factors that influenced their ability to reduce SED across an 8-week intervention to reduce SED in adults with cLBP and elevated depressive symptoms. Methods Three months after a theory-based intervention to break up and reduce sitting, semi-structured interviews explored factors that influenced reducing SED. Three researchers independently coded each conversation. Codes were charted and mapped with participants reviewing their own transcripts and the merged codes. The research team then defined key themes. Factors that were perceived to either facilitate behavior change or acted as barriers were identified and thematized as positive or negative determinants. Results Common barriers for reducing SED included environmental constraints, opposing social norms, and productivity; these barriers were frequently encountered in the workplace. Common facilitators for reducing SED included habit development, self-monitoring tools, restructuring the physical environment, and social accountability. Notably, back pain was not a frequently reported barrier or facilitator for reducing SED. Conclusion This sample of patients with cLBP and elevated depressive symptoms had similar determinants for reducing SED as previously reported in non-patient populations and did not appear to need strategies specific to dealing with chronic pain. Since work-related social norms and environmental factors were perceived as significant barriers to sitting less, workplace interventions that provide standing desks, offer standing meetings rooms, and/or institution-wide standing breaks may help reduce SED at work. The use of an activity monitor with sitting reminders and education regarding how to use the reminders as external cues to develop new sitting habits may also aid in adoption and adherence to this behavior change across settings. Developing coping plans and restructuring physical environments were perceived as successful strategies for overcoming social and environmental barriers. Future interventions targeting SED reductions may benefit from incorporating these strategies.