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In high-elevation or high-latitude permafrost areas, persistent subzero temperatures significantly impact the freeze–thaw durability of concrete structures. Traditional methods for studying the frost resistance of concrete in permafrost regions do not provide a complete picture for predicting properties, and new approaches are needed using, for example, machine learning algorithms. This study utilizes four machine learning models—Support Vector Machine (SVM), extreme learning machine (ELM), long short-term memory (LSTM), and radial basis function neural network (RBFNN)—to predict freeze–thaw damage factors in concrete under low and subzero temperature conservation conditions. Building on the prediction results, the optimal model is refined to develop a new machine learning model: the Sparrow Search Algorithm-optimized Extreme Learning Machine (SSA-ELM). Furthermore, the SHapley Additive exPlanations (SHAP) value analysis method is employed to interpret this model, clarifying the relationship between factors affecting the freezing resistance of concrete and freeze–thaw damage factors. In conclusion, the empirical formula for concrete freeze–thaw damage is compared and validated against the prediction results from the SSA-ELM model. The study results indicate that the SSA-ELM model offers the most accurate predictions for concrete freeze–thaw resistance compared to the SVM, ELM, LSTM, and RBFNN models. SHAP value analysis quantitatively confirms that the number of freeze–thaw cycles is the most significant input parameter affecting the freeze–thaw damage coefficient of concrete. Comparative analysis shows that the accuracy of the SSA-ELMDE prediction set is improved by 15.46%, 9.19%, 21.79%, and 11.76%, respectively, compared with the prediction results of SVM, ELM, LSTM, and RBF. This parameter positively influences the prediction results for the freeze–thaw damage coefficient. Curing humidity has the least influence on the freeze–thaw damage factor of concrete. Comparing the prediction results with empirical formulas shows that the machine learning model provides more accurate predictions. This introduces a new approach for predicting the extent of freeze–thaw damage to concrete under low and subzero temperature conservation conditions.

Bio-inspired self-healing materials hold great promise for applications in wearable electronics, artificial muscles and soft robots, etc. However, self-healing at subzero temperatures remains a great challenge because the reconstruction of interactions will experience resistance of the frozen segments. Here, we present an ultrarobust subzero healable glassy polymer by incorporating polyphenol nano-assemblies with a large number of end groups into polymerizable deep eutectic solvent elastomers. The combination of multiple dynamic bonds and rapid secondary relaxations with low activation energy barrier provides a promising method to overcome the limited self-healing ability of glassy polymers, which can rarely be achieved by conventional dynamic cross-linking. The resulted material exhibits remarkably improved adhesion force at low temperature (promotes 30 times), excellent mechanical properties (30.6 MPa) and desired subzero healing efficiencies (85.7% at −20 °C). We further demonstrated that the material also possesses reliable cryogenic strain-sensing and functional-healing ability. This work provides a viable approach to fabricate ultrarobust subzero healable glassy polymers that are applicable for winter sports wearable devices, subzero temperature-suitable robots and artificial muscles. Self-healing materials hold great promise for applications in wearable electronics, artificial muscles and soft robots but selfhealing at subzero temperatures remains a great challenge. Here, the authors present a robust subzero healable glassy polymer by incorporating polyphenol nano-assemblies with a large number of end groups into polymerizable deep eutectic solvent elastomers.

Supercooled droplet freezing on surfaces occurs frequently in nature and industry, often adversely affecting the efficiency and reliability of technological processes. The ability of superhydrophobic surfaces to rapidly shed water and reduce ice adhesion make them promising candidates for resistance to icing. However, the effect of supercooled droplet freezing—with its inherent rapid local heating and explosive vaporization—on the evolution of droplet–substrate interactions, and the resulting implications for the design of icephobic surfaces, are little explored. Here we investigate the freezing of supercooled droplets resting on engineered textured surfaces. On the basis of investigations in which freezing is induced by evacuation of the atmosphere, we determine the surface properties required to promote ice self-expulsion and, simultaneously, identify two mechanisms through which repellency falters. We elucidate these outcomes by balancing (anti-)wetting surface forces with those triggered by recalescent freezing phenomena and demonstrate rationally designed textures to promote ice expulsion. Finally, we consider the complementary case of freezing at atmospheric pressure and subzero temperature, where we observe bottom-up ice suffusion within the surface texture. We then assemble a rational framework for the phenomenology of ice adhesion of supercooled droplets throughout freezing, informing ice-repellent surface design across the phase diagram.Icephobic surfaces are helpful for increasing safety and sustainability in engineering applications. A study of the behaviour of supercooled droplets freezing on superhydrophobic surfaces now provides insights into ice-repellency mechanisms.

Aqueous rechargeable metal‐ion batteries (ARMBs) represent one of the current research frontiers due to their low cost, high safety, and other unique features. Evolving to a practically useful device, the ARMBs must be adaptable to various ambient, especially the cold weather. While much effort has been made on organic electrolyte batteries operating at low temperatures, the study on low‐temperature ARMBs is still in its infancy. The challenge mainly comes from water freezing at subzero temperatures, resulting in dramatically retarded kinetics. Here, the freezing behavior of water and its effects on subzero performances of ARMBs are first discussed. Then all strategies used to enhance subzero temperature performances of ARMBs by associating them with battery kinetics are summarized. The subzero temperature performances of ARMBs and organic electrolyte batteries are compared. The final section presents potential directions for further improvements and future perspectives of this thriving field. Based on the freezing behavior of water and its effects on subzero performances of aqueous rechargeable metal‐ion batteries (ARMBs), strategies used to enhance subzero performance of ARMBs by associating them with battery kinetics are summarized. The subzero performance of ARMBs and organic electrolyte batteries are compared. Future perspectives of this thriving field are presented.

HighlightsA critical assessment of electrolytes’ limiting factors, which affect the low-temperature performance of Li-metal batteries.Summary of emerging strategies to improve low-temperature performance from the aspects of electrolyte design and electrolyte/electrode interphase engineering.Perspectives and challenges on how to develop creative solutions in electrolytes and correlative materials for low-temperature operation.Electrolyte design holds the greatest opportunity for the development of batteries that are capable of sub-zero temperature operation. To get the most energy storage out of the battery at low temperatures, improvements in electrolyte chemistry need to be coupled with optimized electrode materials and tailored electrolyte/electrode interphases. Herein, this review critically outlines electrolytes’ limiting factors, including reduced ionic conductivity, large de-solvation energy, sluggish charge transfer, and slow Li-ion transportation across the electrolyte/electrode interphases, which affect the low-temperature performance of Li-metal batteries. Detailed theoretical derivations that explain the explicit influence of temperature on battery performance are presented to deepen understanding. Emerging improvement strategies from the aspects of electrolyte design and electrolyte/electrode interphase engineering are summarized and rigorously compared. Perspectives on future research are proposed to guide the ongoing exploration for better low-temperature Li-metal batteries.

• Background and Aims Despite the considerable number of studies on the impacts of climate change on alpine plants, there have been few attempts to investigate its effect on regeneration. Recruitment from seeds is a key event in the life-history of plants, affecting their spread and evolution and seasonal changes in climate will inevitably affect recruitment success. Here, an investigation was made of how climate change will affect the timing and the level of germination in eight alpine species of the glacier foreland. • Methods Using a novel approach which considered the altitudinal variation of temperature as a surrogate for future climate scenarios, seeds were exposed to 12 different cycles of simulated seasonal temperatures in the laboratory, derived from measurements at the soil surface at the study site. • Key Results Under present climatic conditions, germination occurred in spring, in all but one species, after seeds had experienced autumn and winter seasons. However, autumn warming resulted in a significant increase in germination in all but two species. In contrast, seed germination was less sensitive to changes in spring and/or winter temperatures, which affected only three species. • Conclusions Climate warming will lead to a shift from spring to autumn emergence but the extent of this change across species will be driven by seed dormancy status. Ungerminated seeds at the end of autumn will be exposed to shorter winter seasons and lower spring temperatures in a future, warmer climate, but these changes will only have a minor impact on germination. The extent to which climate change will be detrimental to regeneration from seed is less likely to be due to a significant negative effect on germination per se, but rather to seedling emergence in seasons that the species are not adapted to experience. Emergence in autumn could have major implications for species currently adapted to emerge in spring.

Freeze desalination (FD) has several benefits compared to vaporization-based and membrane-based desalination methods. The FD process needs approximately 1/7th of the latent heat required by the vaporization-based desalination processes. The involvement of sub-zero temperature in FD reduces the risk of corrosion and scaling. This paper reviews the advances in FD methods involving stand-alone and hybrid methods that operate with and without utilizing the energy released during the re-gasification of liquefied natural gas. Moreover, the paper discusses the future focus areas for research and development to make FD a commercially feasible technology. Potable water was produced from brackish water and seawater by FD wherein the nucleation was achieved by ice seeding, the mixing of rejected salt from ice into the liquid phase was controlled appropriately, growth of ice crystals was slow, and liquid subcooling was maintained at approximately 4 K. The post-treatment of obtained ice is needed to produce potable water if the process is instigated without ice seeding. The plant capacity of stand-alone progressive FD was higher than the stand-alone suspension FD of seawater. The integration of the falling-film, fractional thawing, and block FD method showed significantly improved plant capacity than the stand-alone suspension FD method. The energy consumption of stand-alone PFC and SFC-based desalination with latent heat recovery was reported close to the reverse osmosis (RO) method. The hybrid (integration of the suspension FD method with membrane distillation) FD method utilizing LNG cold energy consumed less energy than the conventional RO method.

Highlights The unique layered structure and excellent photoelectric properties of MoS 2 facilitate the abundant generation and rapid transfer of photo-excited carriers, which accelerate the CO 2 reduction and Li 2 CO 3 decomposition upon illumination. MoS 2 -based photo-energized Li–CO 2 battery displays ultra-low charge voltage of 3.27 V, high energy efficiency of 90.2%, superior cycling stability after 120 cycles and high rate capability. The low-temperature Li–CO 2 battery achieves an ultra-low charge voltage of 3.4 V at –30 °C with a round-trip efficiency of 86.6%. Li–CO 2 batteries are considered promising energy storage systems in extreme environments such as Mars; however, severe performance degradation will occur at a subzero temperature owning to the sluggish reaction kinetics. Herein, a photo-energized strategy adopting sustainable solar energy in wide working temperature range Li–CO 2 battery was achieved with a binder-free MoS 2 /carbon nanotube (CNT) photo-electrode as cathode. The unique layered structure and excellent photoelectric properties of MoS 2 facilitate the abundant generation and rapid transfer of photo-excited carriers, which accelerate the CO 2 reduction and Li 2 CO 3 decomposition upon illumination. The illuminated battery at room temperature exhibited high discharge voltage of 2.95 V and mitigated charge voltage of 3.27 V, attaining superior energy efficiency of 90.2% and excellent cycling stability of over 120 cycles. Even at an extremely low temperature of − 30 °C, the battery with same electrolyte can still deliver a small polarization of 0.45 V by the photoelectric and photothermal synergistic mechanism of MoS 2 /CNT cathode. This work demonstrates the promising potential of the photo-energized wide working temperature range Li–CO 2 battery in addressing the obstacle of charge overpotential and energy efficiency.

Background Dynamic compressive strength (DCS) of frozen rocks is significant in improving the impact design of rock engineering in cold regions. However, the existing dynamic low temperature testing systems generally cannot achieve a controllable cooling rate or maintain a stable freezing temperature environment, which induces undesirable damage in rocks due to the rapid cooling rate and leads to inaccurate measurement results. Objective The objective of this study is to develop a valid dynamic low temperature testing system capable of testing frozen rocks and investigate the effect of ambient sub-zero temperature on the dynamic compressive behaviors of rocks. Methods The T 2 spectrums obtained by NMR (Nuclear Magnetic Resonance) of two freezing conditions are adopted to prove the necessity of ambient sub-zero temperature for dynamic tests of frozen rocks. A valid dynamic low temperature testing system is developed to perform the dynamic rock test under the ambient sub-zero temperature of dry and saturated white sandstone specimens at 20 °C, -10 °C, and -20 °C. The DCSs (dynamic compressive strength) of dry and saturated porous white sandstones at 20 °C, -10 °C, and -20 °C are obtained and compared. Results The dynamic low temperature testing system is valid for performing the dynamic rock test under ambient sub-zero temperature and capturing the dynamic failure process of frozen rock specimens. At 20 °C, -10 °C, and -20 °C, the DCSs of dry sandstones are higher than those of saturated sandstones, and the sub-zero temperature has a different influence on the DCSs of dry and saturated sandstones, indicating that both the phase transition of water and the shrinkage of minerals contribute to the DCS deterioration. Conclusions Ambient sub-zero temperature of dynamic testing frozen rocks is necessary to evaluate the significant temperature influence on the dynamic compressive behavior of sandstone.

This study evaluates the Noah land surface model (LSM) in its ability to simulate water and heat exchanges over frozen ground in a Tibetan meadow ecosystem. A comprehensive dataset including in situ micrometeorological and soil moisture–temperature profile measurements collected between November and March is utilized, and analyses of the measurements reveal that the measured soil freezing characteristics are better captured by 1) modifying the parameter b₁ implemented in the current Noah LSM that constrains the shape parameter of soil water retention curve utilized by the water potential freezing point depression equation to produce appropriate liquid water content θ liq under subzero temperature conditions and 2) neglecting the ice effect on soil-specific surface and thus matric potential via setting the empirical parameter that accounts for the effect of increase in specific surface of soil particles and ice–liquid water ck to zero. The numerical experiments performed with the Noah model run show that in comparison to the default Noah LSM, adoption of ck = 0 and site-specific b₁ values reduces the overestimation of θ liq across the soil profile. Implementation of augmentations such as the parameterization of diurnally varying thermal roughness length resolves the overestimation of daytime turbulent heat fluxes and underestimation of surface temperature. Further adoption of a new heat conductivity parameterization reduces the overestimation of nighttime surface temperature. An appropriate treatment of phase change efficiency that accounts for changing freezing rate with varying liquid water contents is also needed to reduce the temperature underestimation across soil profiles.