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We demonstrate here a novel method for the design of liquid crystals (LCs) via the cyclization of mesogens by flexible chains. For two azobenzene-4,4’-dicarboxylate derivatives, the cyclic dimer, cyclic bis(tetraethylene glycol azobenzene-4,4′-dicarboxylate) (CBTAD), shows LC properties with smectic A phase, while its linear counterpart, bis(2-(2’-hydroxyethyloxy)ethyl azobenzene-4,4′-dicarboxylate (BHAD), has no LC phase. The difference is ascribed to the shackling effect from the cyclic topology, which leads to the much smaller entropy change during phase transitions and increases the isotropic temperature greatly for cyclics. In addition, the trans-to-cis isomerization of azobenzene groups under UV-light is also limited in CBTAD. With the reversible isomerization of azobenzene groups, CBTAD showed interesting isothermal phase transition behaviors, where the LC phase disappeared upon photoirradiation of 365 nm UV-light, and recovered when the UV-light was off. Combined with the smectic LC nature, a novel UV-light tuned visible light regulator was designed, by simply placing CBTAD in two glass plates. The scattered phase of smectic LC was utilized as the “OFF” state for light passage, while the UV-light induced isotropic phase was utilized as the “ON” state. The shackling effect outlined here should be applicable for the design of cyclic LC oligomers/polymers with special properties.

A broadband wide-angle scanning array antenna with suppressed mutual coupling for 5G Sub-6G mobile communication applications is presented in this letter. To reduce mutual coupling, the metal columns are used in the dipole array antenna. The metal columns are positioned below the edge of the dipole, leading to the improved the impedance matching characteristics and a wider scanning angle. A 18 prototype of the suggested design has been manufactured and tested to ensure its usefulness. The overall dimension is 2.3300.2800.240 (0 is the free space wavelength at 2.5 GHz). The measured and simulated results are quite consistent. The main lobe achieves a scanning range of 60 at 2.5-4.5 GHz (57.1%, active VSWR

Efficient and direct conversion of methane to value-added products has been a long-term challenge in shale gas applications. Here, we show that atomically thin nanolayers of Pt with a single or double atomic layer thickness, supported on a two-dimensional molybdenum titanium carbide (MXene), catalyse non-oxidative coupling of methane to ethane/ethylene (C2). Kinetic and theoretical studies, combined with in-situ spectroscopic and microscopic characterizations, demonstrate that Pt nanolayers anchored at the hexagonal close-packed sites of the MXene support can activate the first C–H bond of methane to form methyl radicals that favour desorption over further dehydrogenation and thus suppress coke deposition. At 750 °C and 7% methane conversion, the catalyst runs for 72 hours of continuous operation without deactivation and exhibits >98% selectivity towards C2 products, with a turnover frequency of 0.2–0.6 s−1. Our findings provide insights into the design of highly active and stable catalysts for methane activation and create a platform for developing atomically thin supported metal catalysts. The challenge in non-oxidative coupling of methane lies in the activation of the first C–H bond while avoiding further dehydrogenations, which lead to the formation of coke. Here, atomically thin platinum nanolayers on two-dimensional molybdenum titanium carbides are reported as a superior catalyst for this reaction owing to reduced coke formation.

Objective: Traditional endoscopic ultrasonography (EUS), which uses one-dimensional (1-D) curvilinear or radial/circular transducers, cannot achieve dynamic elevational focusing, and the slice thickness is not sufficient. The purpose of this study was to design and fabricate a 1.5-dimensional (1.5-D) circular array transducer to achieve dynamic elevational focusing in EUS in vivo . Methods : An 84 × 5 element 1.5-D circular array transducer was successfully developed and characterized in this study. It was fabricated with PZT-5H 1-3 composite that attained a high-electromechanical coupling factor and low-acoustic impedance. The acoustic field distribution was measured with different transmission modes to validate the 1.5-D elevational beam focusing capability. The imaging performance of the 84 × 5 element 1.5-D circular array transducer was evaluated by two wire phantoms, an agar-based cyst phantom, an ex vivo swine pancreas, and an in vivo rhesus macaque rectum based on multifocal ray-line imaging method with five-row elevational beam steering. Results : It was demonstrated that the transducer exhibited a central frequency of 6.47 MHz with an average bandwidth of 50%, a two-way insertion loss of 23 dB, and crosstalk of Conclusion : Dynamic elevational focusing and the enhancement of the slice thickness in EUS were obtained with a 1.5-D circular array transducer. Significance : This study promotes the development of multirow and two-dimensional array EUS probes for a more precise clinical diagnosis and treatment.

This article presents a new direct load voltage control method for electrolytic capacitorless wireless power transfer (WPT) system without dc/dc converter. In specific, the three-phase low-frequency ac to the high-frequency ac (HFac) converter is employed into the electrolytic capacitorless WPT system by using the bidirectional power switches. The HFac voltage is directly generated on the transmitting tank without using the electrolytic capacitor. Furthermore, in order to realize the discretionary and accurate load voltage control without dc/dc converter, the nine voltage vectors, including six effective voltage vectors and three zero voltage vectors, are selectively exported for the transmitting tank with different duty cycles. In addition, the unity power factor correction and direct load voltage control are both achieved only by transmitting side control. Meanwhile, theoretical analysis of double series-compensated transmitting network and duty cycles under resonant frequency calculation in microchip are demonstrated in detail. Finally, both simulation and experimental results are provided to verify the feasibility and correctness of the proposed system, which operates at 85 kHz with 90% efficiency and about 9% total harmonic distortion.

Mechanical instabilities in soft materials have led to the formation of unique surface patterns such as wrinkles and cracks for a wide range of applications that are related to surface morphologies and their dynamic tuning. Here, we report a simple yet effective strategy to fabricate strain-tunable crack and wrinkle microvalves with dimensions responding to the applied tensile strain. The crack microvalves initially closed before stretching are opened as the tensile strain is applied, whereas the wrinkle microvalves exhibit the opposite trend. Next, the performance of crack and wrinkle microvalves is characterized. The design predictions on the bursting pressure of microvalves and others from the theory agree reasonably well with the experimental measurements. The microfluidic devices with strain-tunable crack and wrinkle microvalves have then been demonstrated for microsphere screening and programmable microfluidic logic devices. The demonstrated microfluidic devices complement the prior studies to open up opportunities in microparticle/cell manipulations, fluidic operations, and biomedicine.

This paper addresses the influence of relative density on the particle breakage of non-uniform grading coral sand by 45 one-dimensional compression tests. Dyeing tracking and image segmentation methods are adopted to reveal the particle breakage of the coral sand. The test results show that D50 (1 mm) is the critical size in deciding the breakage possibility. The number of total broken particles and the broken fine particles (d D50) are significantly greater than those of the fine particle groups (d

A two-phase closed thermosyphon (TPCT) with a CuO–H2O nanofluid was used to effectively harness the internal accumulation of thermal energy from a coal pile, formerly subject to the risk of spontaneous combustion. The heat transfer effect of different insertion ratios of the TPCT (evaporation section:condensation section = 1:3, 1:2, and 2:3) and inclination angles (30°, 45°, 60°, and 90°) was investigated for bituminous coal. The results indicated that the heat transfer effect of the insertion ratio, in descending order of preference, was 2:3 > 1:2 > 1:3. When the TPCT insertion ratio was 2:3, the maximum temperature difference was up to 37.7 °C. The heat transfer effects of the TPCT were strengthened when it was inserted at a given angle. In decreasing order of effectiveness, the tested inclination angles showed the following order of preference: 60° > 30° > 45° > 90°. Therefore, 60° was the optimal insertion angle. In general, TPCT has the optimal transfer effects when the insertion ratio is 2:3 and the inclination angle is 60°.

The spontaneous combustion of carbonised and oxidised powders has been long considered an intricate physicochemical process, and their combustion is often concealed and difficult to detect. The self-ignition characteristics and parameters of carbonised and oxidised powders were thus explored. The thermokinetic behaviours of carbonised and oxidised powders (303–1073 K) were assessed at four different heating rates (5.0, 10.0, 15.0, and 20.0 K min−1) through thermogravimetry–differential scanning calorimetry (TG–DSC). The variation of the thermogravimetric curve was obtained, and the apparent activation energy (Ea) of the carbonised and oxidised powders was calculated using the Kissinger–Akah–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods. The LFA457 laser-flash apparatus was employed to measure thermophysical parameters of experimental samples. The results revealed that the TG–derivative thermogravimetry curve shifted towards high temperatures, and overall, the characteristic temperature increased as the heating rate increased (e.g. at heating rates of 5.0–20.0 K min−1, the critical temperatures were 329–349 and 332–356 K for carbonised and oxidised powders, respectively). The Ea values in the combustion stage obtained using the two calculation methods were similar. The Ea values of the carbonised powders were 148.64 (KAS) and 153.58 (FWO). The Ea values of the oxidised powders were 171.23 (KAS) and 175.68 kJ mol−1 (FWO). The specific heat capacity of carbonised powders was higher than that of oxidised powders, whereas the thermal diffusivity and thermal conductivity were lower than those of oxidised powders.

Microbially induced carbonate precipitation (MICP) has been actively investigated as a promising method to improve soil properties. A burning issue impeding its wide application is the severe spatial inhomogeneity of the CaCO3 distribution. Inspiring by the temperature sensitivity of the bacteria activity, a temperature-controlled one-phase MICP method is proposed consisting of two major steps: (1) grouting the specimen with the mixture of cementation and bacteria solutions in a low temperature; (2) inducing CaCO3 precipitation by exposing the specimen to room temperature. A series of experiments are conducted to demonstrate the advantages of the proposed method over the normal two-phase MICP method. Specimens treated with the proposed temperature-controlled method present higher CaCO3 contents with a roughly uniform distribution along the height of the specimen; the strength of those specimens are substantially improved with apparent dilatancy due to the effective bond network formed by the homogeneously distributed CaCO3 precipitation. SEM images indicate that the temperature-controlled method tends to form small crystals distributing uniformly on the grain surface, which may increase the roughness of the grain and the residual stress more effectively.

Driven by the instability of perovskite quantum dots (PQDs), different encapsulation techniques have been used to improve their stability. However, further improvements in the extreme environmental tolerance and polar solvent solubility of PQDs are required to deliver a broader application. How to balance the stability and dispersibility of PQDs in polar solvents is probably the most difficult problem to alleviate in this area. Herein, we promote a facile strategy to construct ultra-stable water-dispersive silica-encapsulated PQDs (PQDs@SiO2-d) by in situ co-hydrolyzing a specially designed triple silane-coupling agent system based on (3-aminopropyl)triethoxysilane (APTES), superhydrophobic perfluorooctyltrimethoxysilane (PFMS), and hydrophilic siloxane terminated polyethylene glycol (Si-PEG). Specifically, protonated APTES (APTES+, from HBr) and APTES are used as alternatives to oleic acid/oleylamine (OA/OAm) ligands, PFMS imparts an excellent resistance to harsh environments, and hydrophilic Si-PEG improves the dispersibility of the resulting material. The PQDs@SiO2-d retains a high PLQY (93%) and presents great dispersibility and stability towards polar solvents. More importantly, the PQDs@SiO2-d can retain a 70% PL intensity after long-term storage under acidic (pH = 1), alkaline (pH = 14), and ionic conditions (PBS buffer solution) for 24 h by regulating the surface hydrophobic and hydrophilic properties of the PQDs. Profiting from these superior properties, the PQDs@SiO2-d can be used directly as a cellular labeling agent for cell imaging.

Co-catalysts have been widely studied to improve photocatalytic water oxidation efficiency, and the precise control of their oxidation states and minimizing particle sizes can optimize the practical performance. In this work, ultrafine cobalt oxide (CoOx) co-catalysts with specific Co valence states have been successfully synthesized, which are anchored on a tantalum oxynitride (TaON) host photocatalyst via a photochemical metal–organic deposition method. Photoelectrochemical and photoluminescence analyses prove that the Co2+ dominant CoOx co-catalyst is favorable for charge separation and transportation because of its excellent hole-capturing properties, consequently enhancing the photocatalytic water oxidation performance. The resultant TaON with the Co2+ dominant CoOx co-catalyst exhibits an outstanding O2 production rate up to 6.10 ± 0.17 mmol h−1 g−1 and possesses an excellent apparent quantum efficiency of 21.2% at 420 nm, which are among the best values of water-oxidation photocatalysts.

Nano-light materials have attracted great interest in materials research due to their excellent fluorescent properties. The hybrid assembly of various nano-optical materials combines their advantages, extending the scope of potential applications. Herein, we report a fluorescence organic–inorganic hybrid nanostructure (T-PNI@QDs) based on binding red-emitting CdTe/ZnS quantum dots (QDs) to blue-emitting aggregation-induced emission (AIE)-active polymeric micelles in aqueous media with dual-channel emission. The AIE-active polymeric micelles were obtained by the self-assembly of thiol-terminated tetraphenylethylene (TPE) functionalized poly(N-isopropylmethacylamide) (T-PNI-SH) in water. An interesting assembly behaviour of transformation from a worm-like to a core–shell structure was observed by controlling the ratio of QDs/polymers due to the coordinated interaction between the QDs and the thiol groups. The dual-emission of T-PNI@QDs has obvious temperature-sensitive behaviour on account of PNIPAM. The novel fluorescent hybrid nanostructure was used as a probe to selectively detect picric acid (PA) in pure water. We expect this work will open up a new perspective for the construction of organic–inorganic hybrids based on different nano-light materials.

Nanoparticles have been extensively found in brittle faults or ductile shear zones, and their formation is closely related to shear movement along the fault plane. However, the formation mechanisms of these nanoparticles are not yet clear. In this study, dolomite samples were triaxially compressed, at a confining pressure of 200–300 MPa, a temperature between 27 °C and 900 °C and a strain rate of approximately 10−5s−1, with a Paterson designed gas medium high-temperature and high-pressure deformation apparatus (HTPDA). Samples deformed at room temperature were characterized by universal microcracks and undulatory extinctions in some grains; when at a temperature between 300 °C and 500 °C, well-developed mechanical twins dominated the microstructure, while at a temperature ≥800 °C, displacements of twin lamellae along a cleavage and a well-developed fracture zone could be seen. Nanoparticles of different shapes were discovered on the slip surfaces of a shear fracture or in microcracks by field emission scanning electron microscopy (FESEM). Nanoparticles on deformed samples under low differential stress were usually of sporadic spherical shapes and uneven distribution; while deformed samples under high differential stress had more dense distributions that were identified. Moreover, grain-overlap and nanofine granulation could be recognized in high strain samples. Based on a mechanical data analysis and microstructural observations, it was suggested that the initial formation of nanoparticles was macroscopically determined by the differential stress subjected to the host rocks, and had nothing to do with temperature; whereas the aggregation morphology of the nanoparticles was related to the temperature during the formation and evolution processes of the nanoparticles.

The damage rule of concrete is theoretically analyzed and discussed from the aspects of the stiffness degradation and the cohesive strength degradation. Further, the multiaxial damage rules of concrete are studied by 25 groups of tests under true triaxial and conventional triaxial compressive cyclic conditions. The analysis of the test results shows that the relationship between the damage variable and the axial plastic strain depends on the loading path. This dependence of the damage variable on the stress paths can be normalized by the equivalent plastic shear strain. A partial differential equation of the damage variable, driven by the equivalent plastic shear strain, is constructed based on two characteristic boundary conditions of the damage gradient. Then, a stress-path-independent isotropic damage variable is proposed by the integral of the partial differential equation. The proposed damage variable can reasonably capture the multiaxial damage behavior of the concrete. The stress path independence of the proposed damage variable is analyzed and further verified by the test results under multiaxial stress conditions.

One-dimensional compression tests on quartz sands treated by microbially induced carbonate precipitation (MICP) were carried out to evaluate the effects of gradation and calcium carbonate (CaCO3) content on compression behaviors. The experimental results reveal that the compressibility of specimens increases with increasing coefficient of uniformity or decreasing CaCO3 content. The evolution of void ratio with vertical stress could be generally characterized into three stages based on the underlying mechanisms. The initiation of bond breakage occurs around vertical stress of 0.036 MPa, and the dominating mechanism transits to particle breakage around vertical stress of 8.3 MPa. Scanning electron microscope analyses demonstrate that bonding effect and coating effect of CaCO3 precipitation are responsible for the lower compressibility of MICP-treated specimen. The presence of small particles leads to more interparticle CaCO3 bonds whose breakage would still allow the small particles to fill the intercoarse-grain voids.

A jet entering a counterflow improves the dilution of contaminant discharged from a chemical factory through pipe. The velocity ratio of jet-to-counterflow and the offset distance of the jet from the boundary significantly affect the dilution efficiency of sewage. A free and an offset round jet, in a counterflow, with ranges of jet-to-counterflow velocity ratios and offset ratios, were experimentally investigated using particle image velocimetry. The time-averaged features, including the mean velocity, penetration length, half-width, and jet centerline were studied. There is a large recirculation region on each side of a free jet in a counterflow. For an offset jet in a counterflow, there is only one large recirculation region on the upper side when the offset ratio is small, due to the wall hinders the entrainment of the counterflow into the jet. As the offset ratio increased, the gap between the wall and jet increased, which resulted in more counterflow entrainment into the jet and the large recirculation region gradually appeared. Accordingly, the penetration length became shorter, as the offset ratio increased for the same jet-to-counterflow ratio. The maximum axial velocity of a free jet in a counterflow decayed more rapidly than that in a quiescent ambient or an offset jet in a counterflow. The profile of excess velocity in the wall normal direction exhibited self-similarity within one half-width of the excess velocity in the established flow region. The half-width of the excess velocity and zero-velocity increased with downstream distance, for a free or an offset jet entering a counterflow. The mixing efficiency of an offset jet entering a counterflow was verified through the distribution of velocity and spreading rate at different streamwise stations.

Polyurethane foam adhesive (PFA) has been introduced as an alternative stabilizer in geotechnical applications because PFA can improve the engineering characteristics of soil by filling the pore space and generating adhesive bonding among the particles. However, the dynamic properties of PFA-reinforced soils are not well understood. To analyze the dynamic characteristics of PFA-reinforced gravels, a series of cyclic triaxial tests were carried out to investigate the shear modulus and damping ratio of PFA-reinforced gravels, and to determine the corresponding effects of the PFA content, confining pressure, consolidation stress ratio and loading frequency. The results showed that the shear modulus increased, and the damping ratio decreased as the PFA content, confining pressure and consolidation stress ratio increased. In contrast, the effect of the loading frequency, which ranged from 0.05 to 1 Hz, was negligible. A modified hyperbolic empirical model can consider the effect of the PFA content on the maximum shear modulus and predict the relationship between the normalized shear modulus and the normalized shear strain was proposed. Moreover, the upper and lower bounds of the damping ratio were also proposed.

CeO2 is an excellent potential material for CO2 hydrogenation attributed to the highly tunable properties including metal–support interaction and abundant oxygen vacancy. In this work, four CeO2 su...

At present, inhibitors have been widely used in the field of coal fire prevention and control, but there are some defects in the use of them. So it is necessary to find a new practical and economical inhibitor. Dissolvable tiny-foam extinguisher (DTE) is environment-friendly, high in thermal stability, and fast in cooling. In view of the good performance of the product, the thermal behavior effects of DTE on coal spontaneous combustion were investigated through experimental tests. A scanning electron microscopy was used to study changes in the surface microstructure of raw coal after DTE treatment. Laser thermal conductivity analysis and simultaneous thermal analysis were used to test the effects of DTE at mass fraction of 0%, 5%, 10%, and 15% on the thermophysical properties, mass loss, characteristic temperature, and heat release of coal during heating. The surface of the DTE-treated coal sample was covered in a dense film. The treated coal sample had lower thermal diffusivity and thermal conductivity values and a higher specific heat capacity. Moreover, coal treated with DTE showed no obvious oxygen absorption or mass gain during initial heating, and the dry cracking temperature was greatly increased by 37 °C, 53 °C, and 100 °C, respectively. The initial heat release temperature increased by more than 170 °C, and the amount of the initial heat absorption was more than 52.2 times that of untreated samples. Oxidation kinetics were applied to calculate the activation energy of the coal during thermal decomposition and ignition, and the activation energies of the treated samples at the thermal decomposition and combustion stages increased by 161%, 179%, and 173%, respectively. From these results, we concluded that DTE could inhibit heat accumulation by blocking oxygen contact with the coal and greatly reducing heat release during heating. Besides, only a small quantity of DTE was needed to effectively inhibit coal self-ignition. These results provide reference for the field application of DTE in restraining coal spontaneous combustion.

The fatigue-creep deformation characteristics and evolutions of microstructure of P/M superalloy FGH96 widely used for the turbine disc of an aero-engine were investigated experimentally. The low cycle fatigue-creep tests with different holding times were performed at 550℃. The influence of the holding time on the stress-strain curve, cyclic strain response, fatigue-creep life and damage mechanism were discussed. The results reveal that the holding time has a significant effect on the fatigue-creep deformation characteristics. As the holding time increases, the hysteretic energy of inelastic strain rises, the steady-state hysteresis curve shifts to the right and the envelope strain and the envelope strain rate increase. Fatigue-creep life decreases firstly exponentially and then stabilizes. The creep damage gradually plays a leading role. The fracture analysis indicates that the introduction of the holding time makes the section appear as a multi-crack source. The fracture mode changes from transgranular fracture to transgranular-intergranular mixed fracture. The slip bands and a small amount of dimples appear in the crack propagation zone and the dimple characteristics of the transient fracture zone are obvious.

This project aims to design a novel passive quasi-zero stiffness vibration isolator (QZS-VI) and analyze the static and dynamic mechanical properties of the QZS-VI. First, a novel combination of V-shaped lever, plate spring and cross-shaped structure (VL-PS-CS) vibration isolation platform is designed, and a nonlinear QZS-VI is built by parallel connecting VL-PS-CS and coil spring. Second, the static and dynamic modeling of QZS-VI are derived considering the geometrical nonlinearity of V-shaped lever and the large deflection of plate spring, and the average method is applied to obtain the displacement transmissibility. Third, the effects of different structural parameters (e.g., the lengths of long arm and short arm of V-shaped lever, the assembly angle between two arms, the thickness of plate spring) on the static mechanical and equivalent nonlinear friction properties of QZS-VI are thoroughly investigated. Finally, the vibration isolation performance of the designed QZS-VI is compared with another QZS-VI of buckled beam mechanism and traditional linear vibration isolator. The QZS-VI with VL-PS-CS fully explores the nonlinear advantages of plate spring and V-shaped lever and can achieve excellent high static and low dynamic stiffness and nonlinear friction properties. The superior static mechanical properties and nonlinear friction of QZS-VI can be tuned with different structural parameters. The designed QZS-VI exhibits much smaller resonant frequency, lower peak value and more stability property at the peak frequency than other isolators due to its special nonlinear friction and stiffness properties. The designed QZS-VI is practical, novel and suitable for low-frequency vibration isolation. The innovative structure provides novel insights into the design of passive vibration isolators and has great potential for application in engineering practice.

In previous experimental studies, the detailed amount of particle breakage under impact loading cannot be obtained due to the coexistence of fragments and unbroken grains in multi-sized sands. In t...

Coal spontaneous combustion (CSC) characteristics were identified by their different types of coal. In this study, the samples of lignite, non-caking coal, lean coal, and anthracite were chosen to ...

Microbially induced calcite precipitation (MICP) can improve the engineering properties of coral sand. The dry density, permeability, unconfined compressive strength (UCS), tensile strength, and mi...

Crushing of grains can greatly influence the strength, dilatancy, and stress-strain relationship of rockfill materials. The critical state line (CSL) in the void ratio versus mean effective stress plane was extended to the breakage critical state plane (BCSP). A state void-ratio-pressure index that incorporated the effect of grain crushing was proposed according to the BCSP. Rowe’s stress-dilatancy equation was modified by adding the breakage void-ratio-pressure index, which was also incorporated into the formulations of the bounding stress ratio and plastic modulus. A BCSP-based bounding surface plasticity model was proposed to describe the state-dependent stress-strain behaviors and the evolution of grain crushing during shearing process of rockfill materials, and was shown to sufficiently capture the breakage phenomenon. Keywords: Constitutive model, Grain crushing, Critical state, Dilatancy, Strength, State parameter

Ultrasonic neuromodulation on large animals, like non-human primates, requires the array transducer to have a good steering ability to arbitrarily stimulate various brain locations. Moreover, due to the different sizes of the animal heads, the array is preferred to be conveniently adjustable to different aperture sizes. To meet these requirements, a scalable 2D plane array, which can consist of up to tens of 256-element square modules, has been designed and fabricated in this study. Arrays with large apertures, consisting of 12 and 48 modules (including 3072 and 12288 elements, respectively), have been assembled and tested. The square modules were driven at a center frequency of 1.04 MHz. The transcranial and steering abilities of the modules were verified in a water tank on an ex vivo macaque skull. A focused beam transmitted by single module could pass through the skull with its peak acoustic pressure reduced to 18.1% of that in the free-field, with an acceptable transverse steering range up to 10 mm. Moreover, a much smaller focal spot was obtained by simultaneous transmission using two vertical-placed modules. Compared to the single module, the focal zone axial size was reduced from 29.7 mm to 3.3 mm, and the "stripes" pattern in the focal zone caused by standing waves was eliminated using a difference-frequency transmitting strategy. Such scalable 2D plane array, which can provide a small-size focal spot and has a large steering range and an acceptable transcranial ability, can be useful in research on ultrasonic neuromodulation on non-human primates.

Rare-earth Nd3+-doped yttrium oxide (Y2O3) is an important near-infrared (NIR) laser material with good chemical and thermal stability. However, the microstructure and energy transition mechanism o...

Neodymium ion (Nd3+)-doped yttrium lithium fluoride (LiYF4, YLF) laser crystals have shown significant prospects as excellent laser materials in many kinds of solid-state laser systems. However, the origins of the detailed information of their local structure and luminescence evolution are still poorly understood. Herein, we use an unbiased CALYPSO structure searching technique and density functional theory to study the local structure of Nd3+-doped YLF. Our results reveal a new stable phase with the P4[combining macron] (No. 81) space group for Nd3+-doped YLF, indicating that the host Y3+ ion site was naturally occupied by the Nd3+ ion impurity. On the basis of our newly developed WEPMD method, we adopt a specific type of orthogonal correlation crystal field to obtain a new set of crystal-field parameters as well as 182 complete Stark energy levels. Many absorption and emission lines for Nd3+-doped YLF are calculated and discussed based on Judd-Ofelt theory, and our results indicate that some of the observed absorption and emission lines are perfectly reproduced by our theoretical calculations. Additionally, we predict several promising transition lines in the visible and near-infrared spectral regions, including the electronic dipole emission lines 4F5/2 → 4I9/2 at 808 nm and 2H9/2 → 4I9/2 at 799 nm, as well as the magnetic dipole emission lines 4F3/2(27) → 4I11/2(6) at 1047 nm and 4F3/2(27) → 4I11/2(8) at 1052 nm. These transition channels indicate that Nd3+-doped YLF laser crystals have greatly promising laser actions for serving as a solid-state laser material.

Coal spontaneous combustion (CSC) is a major problem in coal mining. In the vicinity of underground goaf, secondary or repeated oxidation processes of the residual coal inevitably occur, increasing the risk of coal fires. In this study, the thermal reaction behaviour of two types of raw coal samples and three preoxidised coal samples with different oxidation temperatures (80, 130, and 180 °C) were investigated. The physical and chemical properties of the samples were measured using thermogravimetric analyser-Fourier transform infrared spectroscopy (TGA-FTIR) with heating rates of 1.0, 2.0, 5.0, and 10.0 °C min−1. According to the characteristic temperatures in the heating processes, the entire CSC procedure can be divided into three stages: oxidation, combustion, and burnout. The results indicated that the aliphatic side chain lengths of preoxidised coal were shorter, and the number of branched aliphatic side chains was lower than that of raw coal. Furthermore, the model for the mechanism of preoxidised coal differed from that of raw coal. Average values of the apparent activation energy of the preoxidised coal samples were lower than those of the raw coal samples. Therefore, compared with raw coal, preoxidised coal requires less energy to react and more readily undergoes spontaneous combustion.

Hierarchical porosity and functionalization are recognized as two crucial parameters in mediating the catalytic performance of heterogeneous catalysts, however, they are rarely achieved simultaneously in the development of metal-organic frameworks (MOFs). In this work, a simple and efficient method has been developed to synchronously construct hierarchical porosity and functionalization within a sulfonic acid group functionalized microporous MOF via a palladium-reduction induced strategy, for the first time. The generation mechanism of the mesopore has been explained using two-dimensional 1H DQ-SQ MAS NMR. The content of the mesopore and the active sites within mesoPd@NUS-6 could be finely tuned by simply controlling Pd loading. Particularly, the combination of hierarchical porosity and functionalization, as well as the ultra-stable structure endow the composites with great potential in bulk, for adsorption and heterogeneous catalysis.

A 3D thermo-elasto-hydrodynamic (TEHD) model is presented to study the effects of triangular dimples on the loadcarrying capacity, leakage and friction of a mechanical seal operated under mixed or full film lubrication conditions. The model is solved by the finite element method (FEM), which takes into account the effects of the Jakobsson-Floberg-Olsson (JFO) cavitation boundary condition, surface roughness, elastic-plastic contact, thermo-elastic deformation, and the temperature-viscosity relation. The numerical results of the TEHD model are quite different from those of the hydrodynamic (HD) and thermo-hydrodynamic (THD) models, especially at high speeds. In order to obtain the optimum shape and distribution of the triangular dimples, a comparative study is conducted to investigate different distributions of equilateral triangles and isosceles right triangles. The results show that a surface textured mechanical seal with isosceles right triangular dimples has the most significant hydrodynamic and pumping effects which, in turn, are beneficial to sealing face opening behavior and leakage limitation. The theoretical results are in good agreement with the experimental ones, and offer new guidance for the future design and development of high-speed mechanical seals for aviation piston pumps.

Coal, a flammable substance, is affected by spontaneous weathering and can be hazardous when exposed to thermally unstable conditions. Over the past few decades, numerous chemical disasters involving coal have occurred, resulting in many deaths. Therefore, strategies for the prevention of such disasters must be implemented to ensure human safety, avoid financial losses, and minimise adverse environmental effects. This study determined the thermal safety parameters and thermal hazards of lignitous and long flame coal by using thermogravimetry and differential scanning calorimetry. The characteristics of the functional groups in coal and treated coal were observed through Fourier transform infrared spectrometry. The structures of coal and coal treated with an ionic liquid, namely 1-butyl-3-methylimidazolium, were observed through scanning electron microscopy. Finally, theoretical kinetic models were applied to calculate thermokinetic parameters and identify the degree of thermal hazard present during periods of thermal instability. The results revealed that 1-butyl-3-methylimidazolium nitrate considerably reduced the probability of coal spontaneous combustion and the degree of hazard for long flame coal. Therefore, this ionic liquid could serve as an effective inhibitor of spontaneous combustion in long flame coal.

High-sensitivity detection of acoustic emission from granite under uniaxial stress, together with advanced statistical analysis, shows changing collapse mechanisms when a sample is pre-heated. Massive microstructural changes occur at temperatures >500 °C while low-temperature (<

The correlation between the process parameters of auxiliary ion source and the SiO2 film stress was systematically studied using dual-ion-sputtering deposition. Spectrophotometer and ellipsometer were used to measure the SiO2 film’s transmittance spectrum and reflection ellipsometry. The refractive index and thickness of SiO2 film were obtained by total spectrum inversion calculation. The laser interferometer measures the substrate surface shape to obtain film stress. The experimental result shows that film stress is related to sputtering energy during deposition, high-energy oxygen ion assisted deposition can significantly reduce it and the assisted ion beam voltage plays an important role in controlling it by data normalization analysis. Ultra-low stress high reflective film was prepared by dual-ion-beam sputtering deposition, where stress was 70% lower than traditional film. At the same time, this film can ensure sufficiently high optical quality to keep it reliable and stable in high-precision laser systems.

SiO2 is a very important low refractive index film material that can operate in the UV to mid-IR regions. The SiO2 films used were deposited on Si substrates by different deposition techniques. We designed and manufactured a high-temperature infrared spectrum measuring equipment connected with a Fourier transform infrared (FTIR) spectrometer; the measuring temperature could range from room-temperature to 600°C. The FTIR transmission spectra of SiO2 films under different working temperatures were measured in the wavenumber region from 4000 to 400 cm − 1. From the measured spectra, it can be seen that IBS-SiO2 and IAD-SiO2 films are more stable and operating temperature can reach 400°C. EB-SiO2 film is worse and operating temperature is only 300°C. Complex dielectric functions of SiO2 films under different temperature conditions were calculated from FTIR transmittance spectra, and the best fitted method was obtained for calculating optical constants of dielectric materials in the high temperature condition. The results show that the structure of the Si-O-Si network in IBS-SiO2 films was the most stable structure. The experimental results were of great significance to practical application.

This paper includes an investigation of the thermal conductivity of biocemented soils to better understanding the regimes of heat transmission through soils treated by microbially induced calcium carbonate precipitation (MICP). A series of thermal conductivity tests using the transient plane source method (TPS) was performed on biocemented silica sand specimens with different gradations, void ratios, and MICP treatment cycles. The results showed that MICP treatment greatly improved the thermal conductivity of sand specimens. An increase in uniformity coefficient or a decrease in void ratio of the sand resulted in an increase in the thermal conductivity of MICP-treated specimens for a given MICP treatment cycle. The increment of thermal conductivity of MICP-treated specimens with respect to that of untreated specimens was also affected by gradation, void ratio, and content of calcium carbonate. The greatest improvements in thermal conductivity were achieved for sands having an initial degree of saturation between 0.82 and 0.85. An empirical equation was established to predict the thermal conductivity of MICP-treated silica sand with different variables, which may be useful in designing energy piles in biocemented sand layers. The authors would like to acknowledge the financial support from the National Nature Science Foundation of China (Grant Nos. 41831282, 51922024, and 51678094).

In this paper, a measurement method for electromagnetic parameters of flexible materials based on air coaxial line in low frequency band is proposed. First a material with known electromagnetic parameters and smooth surface is selected as the substrate, the flexible material is attached to the substrate and loaded into the air coaxial line together. Then calibration kits open and short are connected to the terminal of the air coaxial line respectively, and the single-port reflection coefficient of the device is measured by vector network analyzer (VNA). Finally, the electromagnetic parameters of the flexible material are deduced based on the impedance of the specimens section in air coaxial line. Experimental results show that the method proposed in this paper is effective and reliable.