Exploring cost-effective and general approaches for highly active and stable bifunctional transition metal phosphide (TMP) electrocatalysts towards overall water splitting is greatly desirable and ...challenging. Herein, a general strategy combining sol–gel and a carbonization-assisted route was proposed to facilely fabricate a series of TMP nanoparticles, including CoP, MoP, FeP, Cu2P, Ni2P, PtP2, FeNiP, CoNiP, and FeCoNiP, coupled in an amorphous carbon matrix with one-step carbon composite formation. The resultant NiFeP@C exhibits excellent activities as a bifunctional electrocatalyst toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with low overpotentials of 260 and 160 mV, respectively, at 10 mA/cm2 in 1 M KOH solution. With the NiFeP@C electrocatalyst as both electrode materials, an integrated electrolyzer can deliver 47.0 mA/cm2 of current density at 1.60 V, better than the assembled Pt/C20∥IrO2 counterpart. The encapsulation of NiFeP nanoparticles in the carbon matrix effectively prevents their corrosion and leads to almost unfading catalytic activities for more than 20 h for either the HER, OER, or overall water splitting, outperforming recently reported bifunctional electrocatalysts. The coexistence of Ni, Fe, P, and C would have synergetic effects to accelerate charge transfer and promote electrocatalytic activity. This universal strategy for TMP-based composites opens up a new avenue to explore TMPs as multifunctional materials for various applications.
Significant permanent fault rupture may occur during earthquakes and induce adverse effects on pipelines when they are located within a fault zone. Although fault movement–pipeline interaction has ...attracted increasing research attention recently, a simplified method that can be used to directly estimate curvatures of continuous pipelines due to normal fault movement has not been developed. In this study, a systematic finite element (FE) parametric study with 950 FE runs is conducted to investigate normal fault movement–induced bending behavior in continuous pipelines. Centrifuge test results are adopted to verify the numerical model. It is found that ground settlement due to normal fault movement is well captured by an error function. A dimensionless plot is developed between relative pipe–soil stiffness and ratio of maximum pipe curvature to maximum ground curvature. The maximum curvatures of pipelines due to normal fault movement can be estimated directly from the developed dimensionless plot. As the relative pipe–soil stiffness increases from 1.0 × 10
–4
to 1.0 × 10
3
, the curvature ratio decreases from 1 to 0. When the relative pipe–soil stiffness is less than 1.0 × 10
–3
, the curvature ratio is close to 1. In contrast, the curvature ratio is close to zero when the relative pipe–soil stiffness is larger than 10
2
.
Basement excavation may induce unsymmetrical and highly skewed loadings and (or) stress changes in an existing tunnel, not only in the transverse, but also in the longitudinal direction of the ...tunnel. Although basement–tunnel interaction has attracted intense academic interest recently, it is often simply treated as a plane strain problem. In this study, however, based on a dimensional analysis of the governing parameters, two three-dimensional centrifuge tests were designed and carried out in dry sand to investigate the effects of a basement excavation on an existing tunnel located in two horizontal offsets in relation to the basement. In addition, a preliminary three-dimensional numerical analysis was conducted to back-analyse the centrifuge test and to investigate the effects of the tunnel cover-to-diameter and unloading ratios on the existing tunnel. For the specific conditions simulated and soil type tested, a maximum heave of about 0.07% of the final depth of the basement excavation (H
e
) was induced in the tunnel that ran parallel to and beneath the basement. On the contrary, a maximum settlement of 0.014% H
e
was induced in the tunnel located at the side of the basement. For the former tunnel, the influence zone by the basement excavation on vertical tunnel displacement along the longitudinal direction was 1.2L (basement length). By inspecting the measured strains in the longitudinal direction of the existing tunnel, it was found that the inflection point, where the shear force is at a maximum, was located at 0.8L away from the basement centre. Due to stress relief from the basement excavation, the tunnel located directly beneath the basement was vertically elongated, but the one that lay at the side of the basement was distorted. A preliminary numerical parametric study found that tunnel heave decreased as the cover-to-diameter ratio increased, but at a reduced rate.
Measurements of an individual’s water metabolism dynamical information can provide us rich biological information in a noninvasive way. This concept is hindered by the trade-off between the ...sensitivity and responsive velocity of traditional moisture sensors. Herein, inspired by the molecular detecting system based on weak bond interactions in natural organisms, we designed a new concept of a tunable graphene-polymer heterogeneous nanosensing junction by confining a reasonable thickness sensing material into graphene nanochannels. The fundamentally new sensing mechanism based on dynamical hydrogen bonds endows the sensor with over 4 orders of magnitude sensitivity toward a wide range of relative humidity (RH) (from 0% to 97%) with unprecedented fast response (20 ms) and recovery times (17 ms) with little humidity hysteresis. The promising advantages of the sensor allow us to record humidity fluctuation information in real time during a user’s speech and breath, which can both reveal the speech feature and monitor the respiration rate accurately. Importantly, this advanced sensor provides a new opportunity for accurate and reliable physiological and psychological monitoring by detecting the subtlest RH fluctuations on human skin in a noncontact way.
The underground space in urban areas is frequently congested with utilities, including pipelines and conduits, that are affected by underground construction, e.g., tunneling. This paper carries out ...finite element (FE) analyses to investigate the effects of tunneling-induced ground movement on pipelines, with special attention to the different soil responses to uplift and downward pipe–soil relative movements. A series of numerical parametric studies with 900 FE simulation runs in total is performed to encompass various combinations of ground settlement profiles, pipe dimensions, material properties, pipe burial depth, and soil properties that are typical for utility pipelines and tunnel construction in urban areas. The results are summarized in a dimensionless plot of relative pipe–soil stiffness versus ratio of maximum pipe curvature to maximum ground curvature, which can be used to directly estimate the maximum pipe bending strain and (or) to directly assess the tunneling-induced risk to pipelines. The FE results and dimensionless plot are validated against field and centrifuge test results reported in the literature. Effect of pipeline orientation with respect to the tunnel centerline is explored. It might be unconservative if design analysis only considers the case that the pipeline is perpendicular to the tunnel centerline.
Due to shortage of usable spaces in congested urban cities, deep basements for buildings are frequently constructed above or at a side of existing tunnels. Although much attention was paid to the ...basement-tunnel interaction, previous studies mainly simplified it as a plane strain problem and focused on excavation-induced tunnel responses in sand. In this study, three-dimensional centrifuge tests were conducted to investigate long-term tunnel responses due to overlying basement excavation in lightly (overconsolidation ratio (OCR) = 1.7) and heavily overconsolidated (OCR = 6.0) kaolin clays. Immediately upon completion of basement excavation, the measured heave and tensile strain of tunnel in heavily overconsolidated clay are up to 25% smaller than those in lightly overconsolidated clay. This is because a smaller void ratio in a stiffer clay possesses large soil stiffness around tunnel lining. Due to dissipation of excess negative pore water pressure, the maximum heave and tensile strain of tunnel increase by up to 210% and 50%, respectively, in heavily and lightly overconsolidated clays. To ensure the safety and serviceability of existing tunnel, special attention should be paid to long-term rather than short-term tunnel responses.
In this study, an extensive numerical parametric study is conducted in sand to investigate the effectiveness of countermeasures (i.e., methods used to alleviate tunnel deformation) to reduce tunnel ...response due to overlying basement excavation. Centrifuge test results were adopted to calibrate soil parameters and numerical modeling procedures. It is found that the maximum heave and tensile strains (i.e., transverse and longitudinal) of tunnel decrease as an increase in the wall penetration depth. But the reduction in the maximum heave and tensile strains of tunnel is less than 20% when the wall penetration depth is increased by three times. Using a 2 m thick diaphragm wall to replace a sheet pile wall, the maximum transverse tensile strain of tunnel is reduced by up to 27%. The maximum heave and longitudinal tensile strain of tunnel decrease as an increase in the thickness of tunnel lining. However, a slight increase in the thickness of tunnel lining causes an increase in the maximum transverse tensile strain of tunnel. By further increasing the lining thickness, the maximum transverse tensile strain starts to decrease. In terms of the maximum transverse tensile strain of tunnel, a slight increase in the lining thickness may even cause adverse effects on existing tunnels.
Basement excavation inevitably causes stress changes in the ground, leading to soil movements that may affect the serviceability and safety of adjacent tunnels. Despite paying much attention to the ...basement–tunnel interaction, previous research has mainly focused on the influence of tunnel location in relation to the basement, tunnel stiffness, and excavation geometry. The effects of sand density and basement wall stiffness on nearby tunnels due to excavation, however, have so far been neglected. A series of three-dimensional centrifuge tests were thus carried out in this study to investigate these effects on the complex basement–tunnel interaction. Moreover, three-dimensional numerical analyses and a parametric study by adopting a hypoplastic sand model were conducted to improve the fundamental understanding of this complex problem, and calculation charts were developed as a design tool. When the basement was constructed directly above the existing tunnel, excavation-induced heave and strain were more sensitive to a change in soil density in the transverse direction than that in the longitudinal direction of the tunnel. Because a looser sand possesses smaller soil stiffness around the tunnel, the maximum tunnel elongation and transverse tensile strain increased by more than 20% as the relative sand density decreased by 25%. Moreover, the tensile strain induced along the longitudinal direction was insensitive to the stiffness of the retaining wall, but the tensile strain induced along the transverse direction was significantly reduced by a stiff wall. When the basement was constructed at the side of the existing tunnel, the use of a diaphragm wall reduced the maximum settlements and tensile strains induced in the tunnel by up to 22% and 58%, respectively, compared with the use of a sheet pile wall. Under the same soil density and wall stiffness, excavation-induced maximum movement and tensile strains in the tunnel located at a side of the basement were about 30% of the measured values in the tunnel located directly beneath the basement centre.
For the convenience of shoppers and users, there is an increasing demand for the construction of basements in close proximity to existing tunnels. To ensure the safety and serviceability of the ...existing tunnels, attention has been paid to the basement-tunnel interaction. However, a simplified method for direct estimation of tunnel heave and tensile strain due to basement excavation is not available. In this paper, a systematic numerical parametric study is conducted to develop a simplified and approximate method to enable practicing engineers to estimate tunnel response due to overlying basement excavation. This method only considers the effects of excavation geometry, excavation depth, cover-to-tunnel diameter ratio and sand density on tunnel response to basement excavation. An advanced soil model, a hypoplastic sand model, is adopted to simulate soil behaviors. The soil model and soil parameters are calibrated and verified by centrifuge test results. For the tunnel crown located 0.5–1.5D (i.e., diameter) below the formation level of the basement, calculation charts of excavation geometry versus tunnel heave and tensile strain at two relative sand densities (i.e., 68% and 90%) are developed for estimating tunnel responses due to basement excavation. Because denser sand has larger soil stiffness, excavation-induced tunnel heave and tensile strain are found to decrease almost linearly with relatively sand density (Dr) when it varies from 30% to 90%. Thus, excavation-induced tunnel heave and tensile strain at other soil densities can be linearly interpolated by using the proposed calculation charts. An example is provided to illustrate the application of the calculation charts. The tunnel heave and tensile strain predicted from the proposed method are found to be in good agreement with the numerical results.
Cognitive dysfunction is one of the common central nervous systems (CNS) complications of diabetes mellitus, which seriously affects the quality of life of patients and results in a huge economic ...burden. The glymphatic system dysfunction mediated by aquaporin-4 (AQP4) loss or redistribution in perivascular astrocyte endfeet plays a crucial role in diabetes-induced cognitive impairment (DCI). However, the mechanism of AQP4 loss or redistribution in the diabetic states remains unclear. Accumulating evidence suggests that peripheral insulin resistance target tissues and CNS communication affect brain homeostasis and that exosomal miRNAs are key mediators. Glucose and lipid metabolism disorder is an important pathological feature of diabetes mellitus, and skeletal muscle, liver and adipose tissue are the key target insulin resistance organs. In this review, the changes in exosomal miRNAs induced by peripheral metabolism disorders in diabetes mellitus were systematically reviewed. We focused on exosomal miRNAs that could induce low AQP4 expression and redistribution in perivascular astrocyte endfeet, which could provide an interorgan communication pathway to illustrate the pathogenesis of DCI. Furthermore, the mechanisms of exosome secretion from peripheral insulin resistance target tissue and absorption to the CNS were summarized, which will be beneficial for proposing novel and feasible strategies to optimize DCI prevention and/or treatment in diabetic patients.
AQP4-targeted miRNAs can be transmitted through exosomes in peripheral insulin resistance tissues to mediate the communication between central and peripheral cells thereby destroying the main histological and biomolecular basis of the glymphatic system and ultimately inducing cognitive dysfunction. Display omitted
