Search

In response to the deformation and failure of surrounding rock in large section chamber underground roadways of coal mines, this study focuses on the sorting and filling of large section chamber underground roadways in Ulan Mulun coal mine. Similar simulation experiments are conducted using monotonically increasing and constant load uniaxial compression methods to investigate the deformation and failure laws of surrounding rock in large section chamber underground roadways. The results show the following points. ① The failure evolution and deformation displacement trends of the two loading methods are similar in the compaction stage, elastic deformation stage, and micro fracture stable development stage. ② The sample using monotonically increasing loading method has fewer cracks but larger crack gaps. The sample suddenly breaks along the main crack, during which a large amount of debris flies out. The deformation of the sample is mainly concentrated at the boundary of the surrounding rock. More energy is released during the failure, but the duration of energy release after the peak is relatively short. ③ The stress of the specimen loaded with a constant load remains constant, and the strain slowly increases, during which a large number of small cracks are generated. The deformation position of the specimen mainly surrounds the chamber, and the energy released during failure is relatively small, but the duration of energy release after the peak is longer. Based on the deformation and failure law of the surrounding rock of the large section chamber, a bolt and cable support scheme is proposed. A long anchor cable is installed at the top of the chamber to connect the roof and the hard rock above it as a whole. The inclined anchor rods are installed at the coal rock interface of the roadway to tightly connect the coal rock interface with the surrounding rock mass. The numerical simulation results show that after support, the stress, displacement, and plastic zone of the surrounding rock are significantly reduced, the stability of the surrounding rock is greatly improved, and the support effect is good.

In order to investigate the acoustic vibration characteristics of steel-concrete composite (SCC) beams under train excitation, a 50 m simply supported SCC beam on a high-speed railway with a train speed of 400 km/h was taken as the subject. The acoustic vibration responses of the bridge under vehicle load were calculated using a hybrid Finite Element-Boundary Element-Statistical Energy Analysis (FE- BE-SEA) prediction method. The results were compared with those of a concrete simply supported box beam of similar span under the same excitation conditions. The effects of track parameters (such as damping pads) and structural parameters (including deck thickness and diaphragm spacing) on the vibration and acoustic radiation characteristics of the bridge were studied. The results showed that, among the components of the steel-concrete composite beam, the deck exhibited the highest total vibration acceleration level. In most frequency bands, compared with SCC, the vibration and sound responses of concrete beam were significantly lower, with the vibration responses of the concrete web being reduced the most. The damping pads were found to be highly effective in vibration reduction and noise attenuation, particularly in the mid-to-high frequency ranges. Changing the thickness of the bridge deck reduced the structural noise of the SCC. When the deck thickness increased by 50%, the total sound pressure levels (SPLs) of the structural noise changed by -3.0 dB(A) to -2.9 dB(A). Reducing the diaphragm spacing also significantly reduced the structural noise of the bridge. When the diaphragm spacing was reduced by 50%, the total SPLs changed by -5.6 dB(A) to -5.0 dB(A). [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) are promising blocks for building advanced yarns with unique structural and functional attributes. However, the complexity of fabrication and high cost has hindered the widespread adoption of CNT yarns. In this study, a rapid and continuous twisting wet spun yarn strategy to produce highly densified CNT yarns is presented. The method involves effectively dispersing CNTs in the surfactant dispersion, swiftly removing the surfactant in the coagulation bath and twisting treatment to effectively improve the density of yarn and the orientation of CNT. Detailed characterizations on the influence of each spinning conditions reveal that twisting treatment significantly enhances the packing density of yarns, improves the orientation of CNTs, and mitigates the impact of impurities on conductivity. The resulting CNT yarns exhibit a remarkable tensile strength of 600 MPa, a Young's modulus of ≈40 GPa, and a high conductivity of 8990 S cm−1. When utilized as a yarn heater, the CNT yarn demonstrates an ultra‐fast electrothermal response of over 1000 °C s−1 at a low operating voltage of 5 V. Impressively, the mechanical properties of CNT yarns show good stability during heating. This study provides a perspective of structural engineering for the large‐scale preparation of high‐performance CNT yarns. [ABSTRACT FROM AUTHOR]

Fire and smoke detection is crucial for the safe mining of coal energy, but previous fire-smoke detection models did not strike a perfect balance between complexity and accuracy, which makes it difficult to deploy efficient fire-smoke detection in coal mines with limited computational resources. Therefore, we improve the current advanced object detection model YOLOv8s based on two core ideas: (1) we reduce the model computational complexity and ensure real-time detection by applying faster convolutions to the backbone and neck parts; (2) to strengthen the model's detection accuracy, we integrate attention mechanisms into both the backbone and head components. In addition, we improve the model's generalization capacity by augmenting the data. Our method has 23.0% and 26.4% fewer parameters and FLOPs (Floating-Point Operations) than YOLOv8s, which means that we have effectively reduced the computational complexity. Our model also achieves a mAP (mean Average Precision) of 91.0%, which is 2.5% higher than the baseline model. These results show that our method can improve the detection accuracy while reducing complexity, making it more suitable for real-time fire-smoke detection in resource-constrained environments. [ABSTRACT FROM AUTHOR]

In response to the increasingly diverse demands for clothing, self-cooling functional composite fibers composed of boron nitride (BN) nanosheets and aramid nanofibers (ANFs) were produced by using a scalable wet spinning technique. In this technique, the thermal conductive BN nanosheets were aligned along the fiber axis and acted as internal thermal transfer paths, while the ANFs completely wrapped BN sheets around and built a 3D interconnected network, providing excellent mechanical strength to the fibers. The thermal conductivity was significantly improved along the composite fiber axis compared to that of pure ANFs. The thermal imaging study of the fabrics knitted using composite fibers showed prominent heat transfer properties along the fiber axis. This study demonstrates that controlling the alignment of BN nanosheets along the fiber axis plays an important role in manipulating the thermal conductivities of fabrics and could contribute to the generation of self-cooling clothes. [ABSTRACT FROM AUTHOR]

Wearable strain–humidity sensors are increasingly recognized for their role in healthcare and detecting human motion signals. However, many strain–humidity sensors require complex manufacturing processes and have limited applicability. In this study, based on the good miscibility between natural rubber latex (NRL) and poly (3,4‐ethylenedioxythiophene):poly (4‐styrenesulfonate) (PEDOT:PSS), PEDOT:PSS/NRL composite conductors are transferred onto fabric substrate through screen printing and prepared high‐performance strain–humidity sensor. The PEDOT:PSS/NRL blends strain–humidity sensor exhibited good stability and durability (500 cycles) at 10% strain, achieves a gauge factor (GF) of 123.8 with excellent linearity, making it operational in detecting various human motions, such as finger bending, elbow bending, wrist bending, and so on. In addition, the PEDOT:PSS and water molecules interaction results in a humidity response time as low as 0.72 s and recovery time as low as 0.85 s for the PEDOT:PSS/NRL composite strain–humidity sensor, and a wide relative humidity detection range (6–83%), allowing it to be utilized for precise detection of human breathing. Furthermore, it can monitor the use's joint movement, facial muscle movement, and respiratory rate, which show its potential application prospect in health monitoring. [ABSTRACT FROM AUTHOR]

The organic–inorganic composites F70-TiO2, based on fullerene with carboxyl group derivatives and TiO2 semiconductor, have been designed and constructed to become an optical-functional photocatalyst via the facile sol–gel method. The composite photocatalyst obtained shows excellent photocatalytic activity for the high-efficiency conversion of benzylamine (BA) to N-benzylidene benzylamine (NBBA) with air pressure at a normal temperature under visible light irradiation. By optimizing the composition, the composites with the 1:15 mass ratio of F70 and TiO2, denoted as F70-TiO2(1:15), demonstrated the highest reaction efficiency for benzylamine (>98% conversion) to N-benzylidene benzylamine (>93% selectivity) in this study. However, pure TiO2 and fullerene derivatives (F70) exhibit decreased conversion (56.3% and 89.7%, respectively) and selectivity (83.8% and 86.0%, respectively). The UV–vis diffuse reflectance spectra (DRS) and Mott–Schottky experiment's results indicate that the introduction of fullerene derivatives into anatase TiO2 would greatly broaden the visible light response range and adjust the energy band positions of the composites, enhancing the sunlight utilization and promoting the photogenerated charge (e−-h+) separation and transfer. Specifically, a series of results on the in situ EPR tests and the photo-electrophysical experiment indicate that the separated charges from the hybrid could effectively activate benzylamine and O2 to accelerate the formation of active intermediates, and then couple with free BA molecules to form the desired production of N-BBA. The effective combination, on a molecular scale, between fullerene and titanium dioxide has provided a profound understanding of the photocatalysis mechanism. This work elaborates and makes clear the relationship between the structure and the performance of functional photocatalysts. [ABSTRACT FROM AUTHOR]

Stiffened U-rib plates are the elementary components of steel box girders in bridges that directly bear the input external energy before transferring it to other components. Research on the dynamic characteristics of stiffened U-rib plates is the basis for examining vibration and noise in steel box girders. Most relevant studies have focused on the vibrational modes and single-frequency responses in this context, and few researchers have sought to optimize the design of stiffened U-rib plates to reduce responses due to vibrations and noise. This study identifies the global and local laws of vibrational transmission in stiffened U-rib plates subjected to harmonic loads through structural intensity (SI) analysis that is carried out by jointly using standard finite element software and a post-processing code created by the authors. The contributions of each component of vibrational waves are represented to reflect the dominant roles of the bending wave in the baseplate and the in-plane wave in the U-ribs, respectively. The effects of parameters of the U-rib plates on SI are also quantitatively investigated. SI analysis can be used as a new criterion for designing and optimizing bridges as well as formulating measures for vibration reduction. [ABSTRACT FROM AUTHOR]

Due to advantages such as small weight, large load capacity, and easy manufacturing, orthotropic steel decks (OSDs) are widely used in many steel bridges. As an important component of steel bridge decks that bear vehicle loads, OSDs may produce excessive vibrations and corresponding noise due to low dead loads. Therefore, it is important to study the vibration behavior of OSDs to guide the design to reduce vibration and noise in steel bridges. In this paper, the vibration response of an OSD with simply supported boundary conditions is calculated using the modal expansion method. The input mobility and insertion loss are selected as indices to evaluate the vibration response and suppression performance of the bridge. The results of calculations were compared with those of the finite element method to verify their accuracy. They showed that the input mobility of the OSD was affected primarily by the bending stiffness of the corresponding top plate and longitudinal ribs. The vibration energy of the OSD had both frequency-dependent and excitation location-dependent characteristics. When a source acted on the longitudinal rib or was close to it (within a distance of ¼ of the wavelength), the high-frequency vibration response of the OSD could still be greatly suppressed, with an average vibration reduction of approximately 15 dB. Reducing the spacing between the longitudinal ribs is one of the best ways to reduce the vibration response of the OSD. The frequency of the positive insertion loss ranged from 160 to 500 Hz when the longitudinal rib spacing was reduced from 0.8 to 0.4 m. The frequency-related vibration response of the OSD can be further reduced by adding transverse ribs, especially in the high-frequency range. [ABSTRACT FROM AUTHOR]

Idiopathic intracranial hypertension (IIH) is a disorder characterized by elevated intracranial pressure (ICP) that predominantly affects young obese women. IIH is a diagnosis of exclusion. That is, if increased ICP is suspected, magnetic resonance imaging and magnetic resonance venography of the brain are recommended to exclude secondary causes. Imaging findings, such as empty sella, orbital findings, meningocele, and encephalocele, are not diagnostic of ICP, nor does their absence exclude ICP either. Therefore, venous manometry is recommended as the gold standard for evaluation, regardless of previous anatomic imaging results. Venous manometry is an invasive examination that is frequently applied to derive physiologic information concerning the nature of the pressure gradient. However, the pathogenesis of IIH has not been fully elucidated. The presence of venous sinus stenosis in a subset of patients has provided some support for the potential mechanisms underlying this condition. Hence, this review provides an up‐to‐date discussion on the potential pathogenic mechanisms of IIH with a special focus on venous sinus stenosis. Level of Evidence: 1 Technical Efficacy Stage: 2 [ABSTRACT FROM AUTHOR]

The broad application of steel and steel-concrete bridges has caused significant vibration and noise problems. Although the channel steel-concrete composite girder is a commonly used bridge type, the vibration transmission performance and structural optimization design (concrete deck, stiffeners, transverse connection components, etc.) from the perspective of vibration control have not been well studied. In this paper, experimental and numerical approaches are combined to investigate the dynamic properties of a steel-channel girder in the audible frequency range (20–2000 Hz). A steel-channel girder is tested via hammering. The effects of damping, stiffeners, and a concrete deck on structural vibration are evaluated using the finite element method. The experimental results indicate negligible differences in the vibration responses on a single plate, but large differences at different sections. The results are influenced by the effects of the distance and transmission path. The numerical results reveal that increasing the damping and stiffness (e.g., setting stiffeners) are both effective in reducing vibrations. Furthermore, increasing the stiffness has a more prominent effect on structural vibrations and their frequency dependence, whereas increasing the damping ratio can stably reduce structural vibrations. The simulation results indicate that installing a concrete deck is the most effective approach to vibration reduction, as it can decrease overall vibration by more than 10 dB. Vertical web stiffeners have stronger effects on vibration reduction than other stiffening countermeasures (e.g., transverse connection components and longitudinal bottom plate stiffeners). [ABSTRACT FROM AUTHOR]

To effectively and efficiently control vibrations in steel bridge decks, the flexural wave band gap and vibration attenuation mechanism are studied. The band structures and displacement fields of the eigenmodes at the band gap edges of infinite periodic U-rib stiffened plates are calculated. The calculation method is combining the finite element method with Bloch periodic boundary conditions. A scaled specimen test of a finite periodic U-rib stiffened plate is used to validate the numerical results. A comparison of results confirms that introducing the U-rib allows the periodic U-rib stiffened plates to yield several flexural wave band gaps. In the band gaps, flexural wave propagation is stopped and clear flexural vibration suppression is achieved. Furthermore, the effects of geometric parameters and structural schemes on the flexural wave band gaps are analyzed in detail. Finally, by analyzing a specific case, it is demonstrated that the flexural wave band gaps and vibration attenuation properties can be controlled. This provides a new approach to vibration and noise control in steel bridges. [ABSTRACT FROM AUTHOR]

A novel redox-active organic-inorganic hybrid material (denoted as H4TTFTB-TiO2) based on tetrathiafulvalene derivatives and titanium dioxide with a micro/mesoporous nanomaterial structure has been synthesized via a facile sol-gel method. In this study, tetrathiafulvalene-3,4,5,6-tetrakis(4-benzoic acid) (H4TTFTB) is an ideal electron-rich organic material and has been introduced into TiO2 for promoting photocatalytic H2 production under visible light irradiation. Notably, the optimized composites demonstrate remarkably enhanced photocatalytic H2 evolution performance with a maximum H2 evolution rate of 1452 μmol g−1 h−1, which is much higher than the prototypical counterparts, the common dye-sensitized sample (denoted as H4TTFTB-5.0/TiO2) (390.8 μmol g−1 h−1) and pure TiO2 (18.87 μmol g−1 h−1). Moreover, the composites perform with excellent stability even after being used for seven time cycles. A series of characterizations of the morphological structure, the photoelectric physics performance and the photocatalytic activity of the hybrid reveal that the donor-acceptor structural H4TTFTB and TiO2 have been combined robustly by covalent titanium ester during the synthesis process, which improves the stability of the hybrid nanomaterials, extends visible-light adsorption range and stimulates the separation of photogenerated charges. This work provides new insight for regulating precisely the structure of the fulvalene-based composite at the molecule level and enhances our in-depth fundamental understanding of the photocatalytic mechanism. [ABSTRACT FROM AUTHOR]

This paper presents a Nyquist-rate current-steering digital-to-analog converter that achieves a peak spurious-free dynamic range better than 87 dB and a peak signal-to-noise-and-distortion ratio better than 77 dB over a 265-MHz signal band. It is enabled by a fully integrated digital calibration technique that measures and cancels both static and dynamic mismatch errors over the first Nyquist band, and various circuit-level techniques that mitigate the effects of jitter and inter-symbol interference. [ABSTRACT FROM AUTHOR]

An impedance attenuator is implemented to reduce digital-to-analog converter (DAC) distortion, and two techniques to further reduce the distortion are discussed: the first is to use cross-coupled capacitors to cancel nonlinear currents; the second is to optimize the common-mode bandwidth of the differential amplifier for cancellation of distortion. To support these techniques, DAC distortion has been analyzed with the Volterra series, and the analysis is compared with simulation results and measurement data. The analysis uncovers a previously unknown nonlinear cancellation mechanism for the DAC and confirms the proposed techniques. Each technique can contribute 3–6 dB of improvement, and about a 6-dB improvement when combined. The 0.708-mm2 DAC is fabricated in a 28-nm metal-gate digital CMOS process with the proposed impedance attenuator, and it achieves −89 dBc of average HD3 at a 5-MHz input frequency and sampling rate of 230.4 MHz. [ABSTRACT FROM AUTHOR]