In situ high‐pressure Raman spectroscopy experiments have been performed to investigate the structural changes of parabanic acid (PA) up to ~12.0 GPa. The analysis of Raman spectroscopy reveals that ...PA undergoes two phase transitions. The collapse of spacing between molecular layers and the distortion of hydrogen‐bonding networks almost in ac‐plane are the main causes of the first phase transition above 2.1 GPa. The changes of Fermi resonance parameters also provide evidence for the first phase transitions. The second phase transition around 4.0 GPa can attribute to the further reduction of the molecular interlayer spacing and the resulting distortion of hydrogen‐bonding network. First‐principle calculations and Hirshfeld surfaces further confirm the analysis of the experimental results. The analysis of high‐pressure phase transition contributes a better explanation for the high‐pressure phase transition process of layered supramolecular materials with hydrogen‐bond self‐assembly. This study provides the possibility of two new polymorphs for PA under high pressure and is helpful for broadening its potential application of this material, especially in the field of supramolecular chemistry.
The new polymorphs of parabanic acid (C3H2N2O3) were explored by high‐pressure Raman spectroscopy experiments up to 12 GPa. In this work, it was found for the first time that the parabanic acid crystals undergoes two pressure‐induced phase transitions at high pressure of 2.1 and 4.0 GPa because of the rapid collapse of the molecular interlayer spacing and the distortion of the hydrogen‐bonding network.
Gas monitoring in mines and tunnels is the key to ensuring safe production. Nowadays, optical fiber gas sensors depend on the advantages of nonelectrical signal transmission, antielectromagnetic ...interference, corrosion resistance, and small size, which has aroused the interest of researchers. In this direction, this article reviews optical fiber sensors for monitoring common hazardous gases (nitrogen dioxide, hydrogen sulfide, carbon monoxide, ammonia, sulfur dioxide, methane, hydrogen, and carbon dioxide) in mines and tunnels. The adaptability of optical fiber sensors and the characteristics of different optical sensing principles (interferometers, fiber Bragg grating, long-period fiber grating, surface plasmon resonance, and evanescent field) are first discussed. As foundations, the characteristics and sources of various gases, as well as the sensing principles of optical fiber gas sensors, are summarized. Then, the application of optical fiber sensors in hazardous-gas monitoring is discussed. Finally, the current challenges and future trends of optical fiber gas sensors are concluded.
The double pulse test (DPT) is a widely accepted method to evaluate the dynamic behavior of power devices. Considering the high switching-speed capability of wide band-gap devices, the test results ...are very sensitive to the alignment of voltage and current (V-I) measurements. Also, because of the shoot-through current induced by C dv/dt (i.e., cross-talk), the switching losses of the nonoperating switch device in a phase-leg must be considered in addition to the operating device. This paper summarizes the key issues of the DPT, including components and layout design, measurement considerations, grounding effects, and data processing. Additionally, a practical method is proposed for phase-leg switching loss evaluation by calculating the difference between the input energy supplied by a dc capacitor and the output energy stored in a load inductor. Based on a phase-leg power module built with 1200-V/50-A SiC MOSFETs, the test results show that this method can accurately evaluate the switching loss of both the upper and lower switches by detecting only one switching current and voltage, and it is immune to V-I timing misalignment errors.
Most rockbursts are associated with jointed rock masses as the energy stored inside the rock is prone to abruptly release at such discontinuities. Moreover, remote blasting at working faces can ...trigger the brittle failure of jointed rocks at opening boundaries. In this work, a testing system combining true-triaxial compression with dynamic disturbance is employed to investigate the failure modes of cuboid jointed granite specimens. A three-dimensional tunneling-induced stress path is created in cuboid jointed granite specimens by first applying static loads to simulate the stress state encountered around an open boundary. Then, a dynamic disturbance (load) is continuously applied to the granite specimen to simulate the effect of the vibrations experienced due to remote blasting. A dynamic disturbance in the
σ
2
direction is found to reduce the peak strength of the specimen (
σ
p
) by approximately 5% (compared to static stress-induced failure) and promote shearing failure at the fracture surface. The major fracture surfaces form a ‘V’-shape, along with several nearby minor cracks. However, a dynamic disturbance in the
σ
3
direction can reduce the peak strength by 10% and accelerate the evolution of tensile failure resulting in subvertical tensile fracture. Due to the natural stiffness of the joint, the Poisson’s ratio (
υ
3
) in the
ɛ
3
direction is larger than that in
ɛ
2
direction, highlighting the anisotropy of the deformation. The proportion of the total stored energy that is released in the jointed rock is greater than that released in intact hard rock. More strain energy is dissipated at the joint fracture. The joint provides a location at which energy can be released, which considerably increases the severity of potential rockbursts. The energy-storage limit of granite with different dip angles is also explored based on complete stress–strain curves. Post-peak granite specimens with joints dipping at 60° are found to be the most susceptible to external dynamic disturbance but release less kinetic energy. Specimens with joints that dip at 80° incorporate the maximum amount of stored energy and are not prone to rockburst when subjected to dynamic disturbance. Once a rockburst does occur in 80°-dipping jointed granite, a strong tremor will appear, however.
Highlights
Disturbance in σ
2
direction decreases strength by 5% and expedites shearing failure.
Disturbance in σ
3
direction reduces strength by 10% and accelerates tensile failure.
Poisson’s ratio (ν
3
) in ε
3
-direction presents more than that (ν
2
) in ε
2
-direction.
The joint dipping of granite significantly affects energy components of rockbursts.
Sensors suitable for wearable devices have many special characteristics compared to other sensors, such as stability, sensitivity, sensor volume, biocompatibility, and so on. With the development of ...wearable technology, amazing wearable sensors have attracted a lot of attention, and some researchers have done a large number of technology explorations and reviews. However, previous surveys generally were concerned with a specified application and comprehensively reviewed the computing techniques for the signals required by this application, as well as how computing can promote data processing. There is a gap in the opposite direction, i.e., the fundamental data source actively stimulates application rather than from the application to the data, and computing promotes the acquisition of data rather than data processing. To fill this gap, starting with different parts of the body as the source of signal, the fundamental data sources that can be obtained and detected are explored by combining the three sensing principles, as well as discussing and analyzing the existing and potential applications of machine learning in simplifying sensor designs and the fabrication of sensors.
Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a ...nickel foam (NF)-supported MoS2/NiFeS2 heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS2/NiFeS2/NF catalyst achieves a 500 mA cm−2 current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS2/NiFeS2/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm−2, which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm−2, the MoS2/NiFeS2/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS2/NiFeS2/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm−2) far exceed the benchmark RuO2 and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.
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•MoS2/NiFeS2/NF shows ultrahigh activity for OER and HER at large current density.•Ultralow overpotentials (η1000, OER = 314 mV, η1000, HER = 254 mV) are needed.•MoS2/NiFeS2/NF exhibits ultralow cell voltage of 1.79 V@500 mA/cm2 for OWS.•The catalyst shows high stability with no decay in the CP test for OWS over 25 h.
Lane detection is an important task in the field of automatic driving. Since lane lines usually have complex topologies and exist in various complex scenes (e.g., damaged lanes, severe occlusion, ...etc.), lane detection remains challenging. In this work, we propose a Polynomial Global Attention Network (PGA-Net) for lane detection, which is an end-to-end model for mining global road information and predicting lanes shape parameter formulas simultaneously. We model lane shape with cubic polynomial function and use the transformer-based DETR model to introduce the context information of lanes and roads to better regress the lane parameters. For polynomial curve modeling, we propose Mean Curvature Loss (MCL) to constrain the curvature of the predicted lanes, thereby enhancing the quality of curve lanes prediction. In addition, we design an improved supervision strategy to eliminate information bias between our parametric prediction methods and the labeling methods of lane datasets. Our method achieves state-of-the-art performance on two popular benchmarks (TuSimple and LLAMAS) and a most challenging benchmark (CULane), while exhibiting accelerated speed (<inline-formula> <tex-math notation="LaTeX">></tex-math> </inline-formula>140fps on 3090 GPU, 28.9% improvement in average) and lightweight model size (<inline-formula> <tex-math notation="LaTeX"><</tex-math> </inline-formula>3M, an averaged 83.7% reduction). Our code is available at https://github.com/qklee-lz/PGA-Net.
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•Without voids, thrust-induced compressive failure occurs (at shoulders/knees).•With voids, moment-induced tensile failure occurs (at the roof).•The void converts thrust compression ...failure into moment tension failure.•Understanding the failure mode facilitates the design of efficient maintenance.
Small-scale (1:30) model tests were performed to investigate the failure modes of highway tunnels that have single voids with different scales immediately above the lining roof. The tunnels employed have horseshoe-shaped cross-sections which match those typically used to carry two lanes of traffic. In the absence of a void, the mechanical behavior of the tunnel lining is directly related to the ratio of the horizontal to vertical stress, λ. Failure occurs when the compressive stress experienced is high, and the eccentricity is small. Furthermore, it is the shoulders and knees of the tunnel lining that are most susceptible to compressive failure. In the presence of a void, the sign of the bending moment can become reversed, and failure occurs due to bending-induced tension. The intrados of the roof lining is prone to moment-induced tensile stress. It experiences less thrust as well as higher eccentricity which is completely different from the behavior without a void. In other words, the void converts the tendency of the tunnel lining to undergo thrust-induced compressive failure into a tendency to undergo moment-induced tensile failure. When the void angle (angle subtended by the void at the center of the tunnel) is larger than 50°, the failure mode of the tunnel lining is entirely dependent on the void, rather than the earth pressure conditions. That is, the locations and sequence of formation of the cracks formed are almost identical, regardless of the value of λ. Understanding the differences in these failure modes (i.e. with and without voids), should assist in making tunnel maintenance much more efficient. The tunnel lining’s most vulnerable positions can be made less vulnerable by careful choice of the tunnel’s structural parameters, and other supporting measures can be implemented to ensure the safety of the tunnel.
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