The purpose of this paper is to review the development and the state of the art in desiccation cracking characterization methods and review the desiccation cracking behaviors of soils. The review ...begins by briefly introducing in Section 1 the influences of desiccation cracking on soil properties and the significance of studying this topic. Section 2 summarizes the past and existing experimental approaches that have been invented and adopted for soil desiccation cracking investigations at both laboratory and field scales. Various theoretical frameworks formulated to account for the underlying cracking mechanisms are presented in Section 3. Section 4 shows the implementation of theoretical frameworks into mesh-based and mesh-free numerical tools to capture the initiation, propagation, and coalescence of desiccation cracks. Section 5 describes the crack dynamics in desiccating soils, with emphases placed on the coupled process of water evaporation, suction increase, and volume shrinkage, and the crack network evolution. Section 6 discusses major influencing factors of soil desiccation cracking covering soil intrinsic properties, boundary constraints, environmental conditions, and soil admixtures. Finally, a brief summary and proposed prospective research works are presented in Sections 7.
Abstract
Defects can induce drastic changes of the electronic properties of two-dimensional transition metal dichalcogenides and influence their applications. It is still a great challenge to ...characterize small defects and correlate their structures with properties. Here, we show that tip-enhanced Raman spectroscopy (TERS) can obtain distinctly different Raman features of edge defects in atomically thin MoS
2
, which allows us to probe their unique electronic properties and identify defect types (e.g., armchair and zigzag edges) in ambient. We observed an edge-induced Raman peak (396 cm
−1
) activated by the double resonance Raman scattering (DRRS) process and revealed electron–phonon interaction in edges. We further visualize the edge-induced band bending region by using this DRRS peak and electronic transition region using the electron density-sensitive Raman peak at 406 cm
−1
. The power of TERS demonstrated in MoS
2
can also be extended to other 2D materials, which may guide the defect engineering for desired properties.
The search for exotic topological effects of phonons has attracted enormous interest for both fundamental science and practical applications. By studying phonons in a Kekulé lattice, we find a new ...type of pseudospin characterized by quantized Berry phases and pseudoangular momenta, which introduces various novel topological effects, including topologically protected pseudospin-polarized interface states and a phonon pseudospin Hall effect. We further demonstrate a pseudospin-contrasting optical selection rule and a pseudospin Zeeman effect, giving a complete generation-manipulation-detection paradigm of the phonon pseudospin. The pseudospin and topology-related physics revealed for phonons is general and applicable for electrons, photons, and other particles.
Extreme drought events occur more frequently due to climate change. Soil water loss through evaporation is therefore significantly intensified. This study introduces an environment‐friendly and ...sustainable bio‐mediated technique, known as microbially induced calcite precipitation (MICP), for water evaporation suppression in clayey soils. Through lab‐scale evaporation tests, we investigate the effects of cementation solution concentration (0.5, 1.0, and 1.5 mol/L) and MICP treatment procedure (one‐phase and two‐phase MICP methods) on both macroscale (e.g., water loss, desiccation cracking) and microscale (e.g., microstructure variations) behaviors of soils. Experimental results show that MICP is capable of improving water retention capacity and enhancing the inter‐particle bonding of clayey soils. Both water evaporation rate and total water loss decrease with the increasing concentration of cementation solution and the number of MICP treatment cycle. For most testing samples, both one‐phase and two‐phase MICP treatment methods have a similar influence on soil properties. Further microstructure characterizations reveal four key factors contributing to the improved soil response under drying, including dense surface crust, remediated desiccation cracks, smaller pore size and residual solutes. Dense structure of surface crust suppresses the migration of water vapor into the atmosphere. Calcite crystals tend to reduce the evaporation surface if precipitated within cracks, and clog the movement of pore water if precipitated within the soil pore space. This study is expected to improve the fundamental understanding of soil‐atmosphere interactions under MICP treatment and provide insights into the potential application of bio‐mediated technologies as a nature‐based solution for drought mitigation in arid and semi‐arid region.
Plain Language Summary
Drought‐induced log‐term water scarcity in the soil system can have a substantial impact on the ecosystem and environment. For instance, excessive evaporation of soil water caused by drought results in land degradation, salinization, desertification and subsidence. It is clear that maintaining the soil moisture profile by reducing evaporation is vital to the mitigation of negative drought effects on ecosystem in dry areas. This study introduces an environment‐friendly and sustainable bio‐mediated technique, known as microbially induced calcite precipitation (MICP), for water evaporation mitigation in clayey soils. Experimental results show that MICP is capable of improving water retention capacity and enhancing the inter‐particle bonding of clayey soils. Both water evaporation rate and total water loss are significantly decreased after MICP treatment. A relationship between soil moisture evaporation rate and suction is established. This study is expected to improve the fundamental understanding of soil‐atmosphere interactions under MICP treatment and provide insights into the potential application of bio‐mediated technologies as a nature‐based solution for drought mitigation in arid and semi‐arid region.
Adhesion G-protein-coupled receptors (aGPCRs) are important for organogenesis, neurodevelopment, reproduction and other processes
. Many aGPCRs are activated by a conserved internal (tethered) ...agonist sequence known as the Stachel sequence
. Here, we report the cryogenic electron microscopy (cryo-EM) structures of two aGPCRs in complex with G
: GPR133 and GPR114. The structures indicate that the Stachel sequences of both receptors assume an α-helical-bulge-β-sheet structure and insert into a binding site formed by the transmembrane domain (TMD). A hydrophobic interaction motif (HIM) within the Stachel sequence mediates most of the intramolecular interactions with the TMD. Combined with the cryo-EM structures, biochemical characterization of the HIM motif provides insight into the cross-reactivity and selectivity of the Stachel sequences. Two interconnected mechanisms, the sensing of Stachel sequences by the conserved 'toggle switch' W
and the constitution of a hydrogen-bond network formed by Q
/Y
and the P
/V
φφG
motif (φ indicates a hydrophobic residue), are important in Stachel sequence-mediated receptor activation and G
coupling. Notably, this network stabilizes kink formation in TM helices 6 and 7 (TM6 and TM7, respectively). A common G
-binding interface is observed between the two aGPCRs, and GPR114 has an extended TM7 that forms unique interactions with G
. Our structures reveal the detailed mechanisms of aGPCR activation by Stachel sequences and their G
coupling.
Evaporation of water from soils is a three-stage process that has great significance in stress development in exposed geotechnical structures, generation of dusts that can cause environmental ...pollution and respiratory ailments, and dereliction of land by generating drought conditions. In this study, the factors that influence water evaporation from soil have been divided into two categories: external, referring to atmospheric conditions and interior, covering surficial soil characteristics and water content conditions. Particularly, five different sets of laboratory based evaporation tests were performed using cylindrical (150 mm diameter and 7–28 mm height) samples of clayey soil mixed with quartzite sands (three grainsize ranges: 0.2–0.5 mm, 0.5–1.0 mm, and 2.0–3.0 mm) in weight proportions ranging from 0% to 50% to evaluate the effects of soil texture, mineralogy and initial compactive state on its free water evaporation process at room temperature (20–22 °C) and relative humidity (50 ± 2%) conditions. The evaporation tests were performed using mass loss measurements on soil samples to an accuracy of 0.01 g. Findings show that in the first stage of soil drying, water content decreases continuously with time while the ratio of actual to potential evaporation, Ea/Ep stays mostly stable. During the falling rate stage, both water content and Ea/Ep decrease significantly. However, the water content varies but not significantly due to the low value of residual evaporation rate in the residual evaporation stage. Soil with lower sand content starts the falling rate stage at higher water content: 32.52% at added sand proportions of 0% versus 21.87%, 20.65%, 20.45%, 20.26% and 18.34% at added sand proportions of 10%, 20%, 30%, 40%, and 50% respectively. Larger soil sample thicknesses accelerate water evaporation rate and extend the constant evaporation rate stage. Soil particle size was not found to have significant impact on evaporation rate on per unit weight of added soil basis. The evaporation rate increases in direct proportionality to increase in initial water content and dry density.
•Soil characteristics influences moisture evaporation significantly.•Larger soil thicknesses accelerate water evaporation rate.•Higher sand mix proportions lead to larger evaporation rate.•The effect of mixed sand grain size on evaporation is insignificant.•The evaporation rate significantly depends on soil initial compactive state.
•Water infiltration in a cracked soil is investigated.•Effect of drying-wetting cycles is incorporated.•A modified equation is proposed to describe water infiltration in a cracked soil.•The ...relationship between infiltration capacity and surface crack ratio is found.
Infiltration is of great concern in many fields like hydrology, agriculture as well as geotechnical and geological engineering. This study aims to investigate water infiltration in a cracked soil. Infiltration tests were conducted on compacted soil samples with different cracking degrees by drying to various water contents. Three drying-wetting cycles were applied. Experimental results show that no desiccation cracks are observed in the first drying process while cracks initiate and propagate in the second and third drying processes. Different from the infiltration curve of the non-cracked soil sample consisting of two distinct stages, that of the cracked soil consists of three distinct stages, representing constant, rapid reduction and gradual reduction in infiltration rate, respectively. A modified equation is proposed to describe the infiltration behavior of a cracked soil considering the prehealing time of cracks. Furthermore, it is found that for the tested soil, 4% of surface crack ratio is a critical value. When surface crack ratio is smaller than the critical value, its influence on infiltration capacity is insignificant. Afterwards, the infiltration capacity increases dramatically with increasing surface crack ratio. Based on this observation, a piecewise function is proposed to characterize the relationship between the normalized infiltration capacity of cracked soil and surface crack ratio. Infiltration capacity also increases with decreasing initial water content and increasing number of drying-wetting cycles. In terms of steady final infiltration rate, it increases with increasing initial water content as well as increasing number of drying-wetting cycles, but is not affected by desiccation cracking.
A novel type of sticky superhydrophobic cerium dioxide (CeO2) nanotube material is prepared by hydrothermal treatment without any chemical modification. A water droplet on the material surface shows ...a static water contact angle of about 157° but the water droplet is pinned on the material surface even when the material surface is turned upside down. Interestingly, the as‐prepared CeO2 nanotube material displays durable superhydrophobicity and enhanced adhesion to water under ultraviolet (UV) light irradiation. Importantly, this change in water adhesion can be reversed by heat treatment to restore the original adhesive value of 20 µL. Further, the maximum volume of the water droplet adhered on the material surface of CeO2 nanotubes can be regulated without loss of superhydrophobicity during the heating treatment/UV‐irradiation cycling. Meanwhile, the superhydrophobic CeO2 nanotube material shows remarkable thermal stability even at temperatures as high as 450 °C, long‐term durability in chemical environment, and air‐storage and good resistance to oily contaminant. Finally, the potential application in no‐loss water transportation of this sticky superhydrophobic CeO2 material is demonstrated.
The as‐prepared film with the hierarchical structures consisting of microbundles and secondary open‐ended CeO2 nanotubes shows superhydrophobicity and high water adhesion without any chemical modification. The obtained film displays a UV‐durable superhydrophobicity but UV/heat‐induced reversible water adhesion. This film also has good resistance to high temperatures, different pH values, and air‐storage and oily contamination.
Blue phosphorus is a new graphene-like material which has already been proven thermostable in theory, and the synthesis of it on experiment can also be expected. Here, we have investigated the ...electronic structures and carrier mobilities of armchair and zigzag monolayer blue phosphorus nanoribbons (PNRs) and nanotubes (PNTs) using density functional theory combined with Boltzmann transport method with relaxation time approximation. It is found that both PNRs and PNTs are indirect-gap semiconductors with a considerable energy gap. The numerical calculation results indicate that the armchair PNTs, zigzag PNTs, and armchair PNRs have the characteristics of p-type semiconductors in electrical conduction, because the hole mobility is over 1 order larger than the electron mobility. However, the electron mobility is greater than the hole mobility in zigzag PNRs. Owing to the existing p x orbitals (in-plane and along ribbon direction), which are very sensitive to the atomic structure strain, the band edges will be significantly changed under strain which results in a linear decrease of the gap of PNRs and PNTs with deformation aggravation. The charge mobilities can also be effectively regulated by the strain.
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