Calcareous sand containing weak particles originated from the deposition of skeletal residue of marine organisms is susceptible to significant particle crushing under compression and shearing. The ...breakage of grains results in excessive deformation and foundation failure. This study focuses on the mechanical properties and particle crushing of calcareous sand retrieved from Nansha Island, South China Sea. A series of isotropically drained and undrained triaxial compression tests were performed on reconstituted calcareous sand samples at different initial densities and at a wide range of confining stresses. The amount of particle crushing for calcareous sand after shearing was measured and quantified. Experimental results demonstrate that the shear response of calcareous sand had been well interpreted within the critical state framework. The amount of particle crushing for calcareous sand increases with increasing density and confining stress. Compared with the undrained condition, a larger amount of particle crushing of calcareous sands is observed in the drained triaxial compression test. Stress-dilatancy curves exhibit similar varying tendency for calcareous sand. Multiple critical state lines for calcareous sands with different initial densities are identified in the void ratio and logarithm of the mean stress plane. Considering the variation in stress ratio at the critical state induced by particle crushing, all stress paths are normalized to determine the state bounding surface for calcareous sand at varying densities and stresses.
•Particle crushing for calcareous sand is jointly governed by density, stress level, and drainage condition.•Particle crushing-induced position shift of critical state line is observed for calcareous sand.•Bounding state surface is identified for calcareous sand at various initial densities.
Vehicular ad-hoc networks (VANETs) have been emerging based on the state-of-art technologies in wireless and network communications. The message authentications between vehicles and roadside units ...are essential for the security of VANETs. Messages should be signed and verified before they could be trusted. The real identity of vehicles should not be revealed, but which is only traceable by authorized parties. Existing solutions either rely heavily on a tamper-proof hardware device or cannot satisfy the security requirement. Communication overhead as another issue has also not been well addressed in previously reported studies. To address these issues, in this paper, we propose the SPACF scheme that is based on software without relying on any special hardware. We use the Cuckoo filter and the binary search methods to achieve higher success rate than the previous schemes in the batch verification phase. In order to guarantee that it can satisfy message authentication requirement, existential unforgeability of underlying signature against adaptively chosen-message attack is proved under the elliptic curve discrete logarithm problem in the random oracle model. The evaluation results show that our proposed scheme is more efficient than the previous schemes since it is pairing free and does not use map-to-point hash functions, and it satisfies security and privacy requirements of vehicular ad hoc networks.
As the first example of a photocatalytic system for splitting water without additional cocatalysts and photosensitizers, the comparatively cost‐effective Cu2I2‐based MOF, Cu‐I‐bpy ...(bpy=4,4′‐bipyridine) exhibited highly efficient photocatalytic hydrogen production (7.09 mmol g−1 h−1). Density functional theory (DFT) calculations established the electronic structures of Cu‐I‐bpy with a narrow band gap of 2.05 eV, indicating its semiconductive behavior, which is consistent with the experimental value of 2.00 eV. The proposed mechanism demonstrates that Cu2I2 clusters of Cu‐I‐bpy serve as photoelectron generators to accelerate the copper(I) hydride interaction, providing redox reaction sites for hydrogen evolution. The highly stable cocatalyst‐free and self‐sensitized Cu‐I‐bpy provides new insights into the future design of cost‐effective d10‐based MOFs for highly efficient and long‐term solar fuels production.
No additives required: A low‐cost Cu2I2‐based MOF exhibits efficient photocatalytic H2 production without additional photosensitizers and cocatalysts. DFT calculations reveal a good band alignment with the water redox energy levels. The proposed mechanism demonstrates that Cu2I2 clusters in Cu‐I‐bpy (bpy=4,4′‐bipyridine) serve as photoelectron generators to accelerate copper(I) hydride interaction for hydrogen evolution.
Noncovalent interactions between all the neighboring components in biomolecular machines are responsible for their synchronized motion and thus complex functions. This strategy has rarely been used ...in multicomponent molecular machines. Here, we report four 3rotaxane‐based molecular shuttles. Noncovalent interactions among the three components (two interacting macrocycles and one axle) not only cause a “systems‐level” effect on the relative positions of the two macrocycles along the axle, but also result in a synchronized motion of the two macrocycles when adding partial amount of stimuli. Moreover, the intermediate state with one shuttled macrocycle even exist predominantly in the solution during the titration of stimuli, which is theoretically unexpected for the 3rotaxane with two non‐interacting rings. This biomimetic strategy may provide a method for constructing highly complex molecular machines.
Molecular machines: Four 3rotaxane‐based molecular shuttles with two interacting macrocycles have been synthesized. The interactions among the three components (two macrocycles and one axle) were shown to not only affect the relative positions of the macrocycles along the axles with different spacer lengths, but also cause a synchronized motion of the two macrocycles when adding stimuli.
Swirling flow is a common phenomenon in engineering applications. A numerical study of the swirling flow inside a straight pipe was carried out in the present work with the aid of the commercial CFD ...code fluent. Two-dimensional simulations were performed, and two turbulence models were used, namely, the RNG
k–
ε model and the Reynolds stress model. Results at various swirl numbers were obtained and compared with available experimental data to determine if the numerical method is valid when modeling swirling flows. It has been shown that the RNG
k–
ε model is in better agreement with experimental velocity profiles for low swirl, while the Reynolds stress model becomes more appropriate as the swirl is increased. However, both turbulence models predict an unrealistic decay of the turbulence quantities for the flows considered here, indicating the inadequacy of such models in simulating developing pipe flows with swirl.
Rotaxane‐based molecular shuttles are often operated using low‐symmetry axles and changing the states of the binding stations. A molecular shuttle capable of directional shuttling of an ...acid‐responsive cone‐like macrocycle on a single‐state symmetric dumbbell axle is now presented. The axle contains three binding stations: one symmetric di(quaternary ammonium) station and two nonsymmetric phenyl triazole stations arranged in opposite orientations. Upon addition of an acid, the protonated macrocycle shuttles from the di(quaternary ammonium) station to the phenyl triazole binding station closer to its butyl groups. This directional shuttling presumably originates from charge repulsion and an orientational binding preference between the cone‐like cavity and the nonsymmetric phenyl triazole station. This mechanism for achieving directional shuttling by manipulating only the wheels instead of the tracks is new for artificial molecular machines.
Directional shuttling was achieved with an acid‐responsive cone‐like macrocycle on a single‐state symmetric dumbbell axle due to charge repulsion and the orientational binding preference of the macrocycle for the nonsymmetric binding station. This operating mechanism, involving manipulating wheels instead of tracks, is new for artificial molecular machines.
Hadal trenches are the deepest and most remote regions of the ocean. The 11-kilometer deep Challenger Deep is the least explored due to the technical challenges of sampling hadal depths. It receives ...organic matter and heavy metals from the overlying water column that accumulate differently across its V-shaped topography. Here, we collected sediments across the slope and bottom-axis of the Challenger Deep that enable insights into its in situ microbial communities. Analyses of 586 metagenome-assembled genomes retrieved from 37 metagenomes show distinct diversity and metabolic capacities between bottom-axis and slope sites. 26% of prokaryotic 16S rDNA reads in metagenomes were novel, with novelty increasing with water and sediment depths. These predominantly heterotrophic microbes can recycle macromolecules and utilize simple and complex hydrocarbons as carbon sources. Metagenome and metatranscriptome data support reduction and biotransformation of arsenate for energy gain in sediments that present a two-fold greater accumulation of arsenic compared to non-hadal sites. Complete pathways for anaerobic ammonia oxidation are predominantly identified in genomes recovered from bottom-axis sediments compared to slope sites. Our results expand knowledge of microbially-mediated elemental cycling in hadal sediments, and reveal differences in distribution of processes involved in nitrogen loss across the trench.
The large amount of driving data can help intelligent vehicles make decisions to drive safely, improve vehicular services and enhance driving experience. In traditional vehicular networks, data ...sharing needs to be done with roadside units (RSUs). However, RSUs cannot be entirely trusted and the data stored in the RSUs may be tampered with. In addition, the deployment of RSUs along roads consumes a large amount of social resources. Further, data sharing between vehicles lacks a trusted environment, and vehicles may be unwilling to share data with others because of data security and privacy concerns. Moreover, in the event of unauthorized data sharing, the source of the leaked data is difficult to trace. In this study, we exploit consortium blockchain technology to achieve traceable and anonymous vehicle-to-vehicle (V2V) data sharing, effectively preventing second-hand sharing of data. The combination of 5G and blockchain makes it possible to share data without using RSUs. We design an enhanced delegated proof-of-stake consensus algorithm to make it more suitable for applications in the distributed Internet of Vehicles (IoV). A comprehensive analysis shows that the proposed scheme is secure and efficient.
As a significant n-type semiconductor, MoO x (2 ≤ x ≤ 3) micro-/nanostructures with well-tuned shapes, sizes, crystalline phases, and compositions have attracted great attention in the past few ...decades due to remarkable performances in numerous fields of photodevices, energy storage and conversion, gas sensing and catalysts. Additionally, the cheapness, nontoxicity, and ecofriendly nature as well as semiconducting properties also endow them with competitive advantages for their practical applications. However, a comprehensive review on morphological MoO x micro-/nanostructures is still lacking so far. Hence, it is necessary to thoroughly summarize the recent advances made in function-oriented MoO x -based architectures. In this review, we have highlighted the progress in diversified MoO x micro-/nanostructures, including the general synthetic strategies for the synthesis of zero-, one-, two-, and three-dimensional MoO x micro-/nanostructures and the modification (such as doping and hybridization) of MoO x -based composites for enhanced performances in diversified applications (including photodetectors, photothermal therapy, surface-enhanced Raman scattering, supercapacitors, ion batteries, solar cells, gas sensors, multiphase catalysts, photodegradation, hydrogen evolution reaction, and chemical template). Finally, we briefly summarize the present issues and share promising research perspectives emerging from the fascinating MoO x materials.
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