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In this work, the second harmonic generation (SHG) technique based on embedded piezoelectric (PZT) sensors is developed for the defect assessment of concrete samples. Three different imperfection f...

This paper presents the development of a nonlinear vibro-acoustic modulation technique based on non-contact piezoelectric sensors to detect the crack progression of concrete subjected to both mechanical and thermal load. Two types of crack are investigated in the work including the isolated single crack induced by the three point bending test and distributed mapping cracks caused by heating treatment. Experimental results show that the damage index defined in the air-coupled wave modulation method – ultrasonic nonlinear parameter presents a positive correlation with the growth of single crack in bending test and the accumulation of mapping crack in thermal test. The sensitivity of developed method is validated through a comparison between the ultrasonic nonlinear parameter and two traditional linear parameters namely the phase velocity of Rayleigh wave and resonance frequency of vibrations. X-ray Computed Tomography (CT) technique and three-dimensional (3D) image reconstruction method are used to visualize microstructure of thermal damage. The CT images show that proposed nonlinear parameter is reliable and well correlated with the microstructural defects of concrete specimen. The repeatability of the air-coupled method is better than the contact method because the coefficient of variation of non-contact measurements is averagely about 43.2% of the contact measurements. Due to the advantage of removable characteristic of non-contact ultrasonic measurements, the developed air-coupled nonlinear wave modulation method could be promising for fast damage assessment of concrete structures in engineering practice.

A new method is proposed to solve edge cracking and corrosion in rolling process of the magnesium alloy plate. Usually in the process, the edge cracking is caused by the great temperature difference between the edge and the center of the alloy plate and the corrosion is by water in air. The method uses hot air wrapped around the plate to perfectly prevent edge cracking and corrosion. The method also includes cathodic protection for the magnesium alloy based on electrochemistry. The suppression of cathodic protection on the chemical activity of the magnesium alloy was studied. The experiment shows that the new method of edge heating with hot air wrapping is effective to prevent edge cracking and corrosion. Also, the cathodic protection can effectively suppress the chemical activity of the magnesium alloy and improve the surface quality in the rolling process of the magnesium plate, which provides a new concept in rolling process of the magnesium alloy.

We described herein a unique dual emission switching process from o-carborane–tetraphenylethene (TPE) dyads induced by twisted intramolecular charge transfer (TICT) in the crystalline state. Two novel o-carborane–tetraphenylethylene dyads, composed of a TPE core bearing o-carborane units, were designed, synthesized and characterized. Crystalline o-1 and o-2 were obtained with mono-substituted and bi-substituted o-carborane units, respectively. Both dyads presented locally excited (LE) emission and TICT induced emission in solutions. Crystalline o-1 demonstrated aggregation-induced emission (AIE), crystallization-induced emission (CIE), thermochromism, vapochromism, and mechanical luminescence (MCL) properties via TICT, while crystalline o-2 showed only the AIE and CIE properties orginating from the inherent ICT states. From the mechanistic investigations and theoretical calculations, it was demonstrated that the emission was reversible and switchable between green and orange colors for o-1, which was assigned to the facile TICT modulation in the solid state. The results manifest that the unique three-dimensional o-carborane cluster's structure plays an important role in precisely controlling the molecular packing patterns and conformations to achieve TICT emission.

To design and synthesize materials for alkaline hydrogen evolution is favorable for industrial hydrogen cycle operation. In this study, we present a facile approach to synthesize free-standing ruthenium-beryllium (RuBe) nanosheets, which possess amorphous phase state and associated with holey structures due to the molten method. The two-dimensional RuBe nanosheets exhibit improved activity than pure Ru counterpart and comparable properties to commercial Pt toward hydrogen evolution reaction in both of alkaline and neutral electrolytes. Based on the experiments and density functional theory calculations, it is suggested that the adsorption and dissociation of water molecules on Ru-based catalyst are much enhanced with the assistance of Be modulation, which are essential for the improved hydrogen production capability under alkaline condition. This work broadens the Ru-based catalyst family and may provide new insights for electrocatalyst development.

Ultrasonic-assisted grinding processing can effectively reduce the surface roughness and enhance the processing efficiency in the processing of hard and brittle materials. However, the most common ultrasonic assisted grinding is a type of contact ultrasonic grinding where the grinding tool directly contacts the workpiece, which means that it is necessary to accurately control the pre-pressure of the grinding tool on the workpiece. The control of pre-pressure will inevitably increase the complexity of the grinding device, and it is easy to wear the workpiece because of improper pre-pressure control. In this paper, a non-contact ultrasonic grinding method is proposed and the machining mechanism of non-contact ultrasonic grinding is revealed. The resonant frequency of the ultrasonic vibration system and vibration amplitude of the grinding tool working face were simulated and experimentally tested, respectively. Then, the experiment of non-contact ultrasonic grinding of a sapphire wafer was carried out. The result showed that non-contact ultrasonic grinding of the sapphire wafer could reduce the surface roughness by 48.6%. Compared with traditional contact grinding of sapphire wafer under certain pre-pressure conditions, the experimental results show that non-contact ultrasonic grinding has better effects in reducing surface roughness, improving processing efficiency, and improving the quality uniformity of the workpiece machining surface.

Reduced graphene oxide wrapped hollow molybdenum trioxide nanorods (MoO 3 @rGO) have been fabricated by a facile process. The MoO 3 @rGO shows improved lithium storage performance. It could deliver a high reversible capacity (842 mAh/g at 0.1 A/g), excellent cycling stability (778 mAh/g at 0.1 A/g after 200 cycles) and excellent rate capability (455 mAh/g at 2 A/g). The excellent electrochemical performance could be attributed as the special core (MoO 3 )/sheath (rGO) structure, which could accommodate the volume change of MoO 3 during lithiation/delithiation process. In addition, the rGO coating layer could improve the electronic conductivity of MoO 3 .

This project uses the Peltier effect to optimize the temperature control system of the thermostat, uses semiconductors to generate temperature differences, and then forms a heat pump, uses the conversion between high and low taste energy to replace the compressor for refrigeration and temperature adjustment, and at the same time uses the gas vortex characteristics to exchange gas and Adapt and improve the heat dissipation and other aspects. The incubator designed in this project is more excellent in terms of energy saving, low noise and service life, and improves the utilization of energy and resources. At the same time, the temperature control of the incubator has the advantages of stability and accuracy, which can effectively solve the problem of food and medical the deterioration and loss of supplies.

Heteroatom-doped carbon nanomaterials with well-defined porous are used as anode materials for SIBs due to their exceptional structural characteristics. In this work, porous N-doped carbon networks composed with ultrathin carbon nanosheets were synthesized via the direct pyrolysis of Vitamin B5. The content of nitrogen, specific surface area, porous structure of the N-doped carbon nanosheet networks were adjusted by changing reaction temperatures. The formation mechasim of the ultrathin N-doped carbon nanosheet networks was also proposed. The generation of calcium carbonate/calcium oxide used as a self-template renders the formation of the porous structure via thermal treatment. The optimized samples possess a superior lithium and sodium storage: 1534 mAh g −1 at 100 mA g −1 vs. Li/Li + and 335 mAh g −1 at 100 mA g −1 vs. Na/Na + , with nearly 100% cycling Coulombic efficiency, remarkable cycling retention and high rate capacity. Additionally, good electrocatalytic activity for ORR via a 4e −1 pathway determines that the resulting primary Zn-air battery showed high discharge power energy density (80 mW cm −2 ), high reversibility and stability over continuous cycles.

An experimental study on a rotating detonation engine model using hydrogen/air mixture as propellant was conducted to analyze the initiation characteristics of detonation wave. Three ignition methods, including the ordinary spark plug, high-energy spark plug and thermal-jet tube, were used in the tests. The initiation process of rotating detonation wave was recorded and analyzed by a high frequency pressure measurement system and high-speed photographs. Operating range of the model engine was determined by series of experiments. Results indicate that the model engine could be successfully run by all the three ignition methods. Although the detonation formation time using spark plugs is quite stochastic, increasing the ignition energy can reduce the formation time of the detonation wave. Among the three ignition methods, thermal-jet provides the shortest detonation formation time. It is also found that the operating characteristic of the model engine is independent of the ignition device in the same operating condition. Three operation modes of the engine model have been observed, which are failed initiation of the detonation, unstable detonation and continuous rotating detonation. The experimental results show that the stable operating range can be extended by increasing the fuel mass flow rate.

Germanium (Ge) has been considered as a promising anode material for Li-ion batteries because of its theoretical capacity (1600 mA h g−1). However, its poor electrochemical performances resulting from the large volume variation during Li–Ge alloy/dealloy processes prevent its practical application. Herein, we designed a 3D core/shell structure by encapsulation of Ge in a sulfur (S) and nitrogen (N) co-doped three-dimensionally (3D) interconnected macroporous carbon matrix (denoted as Ge@S,N-3DPC). The 3D porous structure can not only buffer the volume change during alloy/dealloy processes, but also facilitate the electrolyte to soak in, offering fast ion/electron pathways. What's more, the co-doping of S and N in carbon could introduce more defects and active sites, which can also help to improve the interfacial adsorption and electrochemical behaviors. When used as an anode material for LIBs, the Ge@S,N-3DPC shows excellent electrochemical performances (1000 mA h g−1 at 200 mA g−1), outstanding cycling stability (94% capacity retention after 300 cycles) and high rate capability (358 mA h g−1 at 10 A g−1). This work develops a general strategy to improve the electrochemical performance of these alloy-type electrode materials with huge volume change in the energy storage area.

The Sb encapsulated in S and N co-doped three-dimensionally (3D) interconnected macroporous carbon composite (denoted as Sb@S,N-3DPC) has been fabricated by using silica opals as hard template following a carbonization process. The structural and morphological characterizations reveal the uniform 3D-network structure with the Sb nanoparticles embedded homogeneously in the carbon spherical shell. The Sb@S,N-3DPC electrode shows a high reversible capacity of 482 mAh g −1 at 100 mA g −1 , displaying good capacity stability (~93% of the initial discharge capacity after 500 cycles at 100 mA g −1 ). The electrode displays superior rate capability and ultralong cyclability (255 mAh g −1 at 2 Ag −1 after 2000 cycles) and also reveals a good rate capability that maintains 160 mAh g −1 at 5 Ag −1 . The excellent electrochemical performance of the Sb@S,N-3DPC is attributed to the 3D-porous carbon network structure and uniform distribution of Sb nanoparticles in carbon matrix, enhancing the conductivity, holding the structure integrity, and thus improving the cycling performance of the anode material. In addition, sulfur and nitrogen co-doping introduced more defects and active sites to the carbon framework, thereby improving the interfacial adsorption and electrochemical behaviors.

This paper uses DPM model in Fluent to divide the mesh and conduct fluid analysis for the existing family filter, by using the Rosin - Rammler distribution simulated reality of different diameter of the plastic particles’ distribution in the water. Secondly, using particle tracking algorithm to calculate the distribution of particle diameter of the export, so as to check the existing household filter’s ability for the different plastic particle diameter.

This device combines phase change heat storage with air circulation, and proposes a new three-dimensional honeycomb grid structure on the phase change material carrier structure. The reasonable use of steam residual heat and the use of a segmented electromagnetic coil structure reduce the heat loss and power consumption of IH rice cooker. Utilizing the hot steam generated in the heating stage of the rice cooker, the low-temperature waste heat is recycled in the low-temperature phase-change thermal storage module designed by the device. At the same time, the electromagnetic coil is segmented. Besides, the fuzzy control is used to determine the actual amount of rice to be cooked to determine the number of coil segments used in the heating stage to reduce power consumption.

In this paper, a fully non-contact second harmonic generation (SHG) technique using a pair of air-coupled ultrasonic transducers is developed and the feasibility of the technique is investigated through the evaluation of surface cracks of concrete beams subjected to the bending load. The reliability of developed technique is subsequently validated by comparing the non-contact nonlinear ultrasonic measurements with measurement results based on contact-type sensors, where the coefficient of variation of non-contact measurements is averagely about 46% of the contact measurements. The defined nonlinear parameter is found to have a monotonically increasing trend with the growth of concrete crack, and the nonlinear parameter corresponding to the largest crack increases about 7 times from its initial value corresponding to the sample in intact state. In contrast, the increase of linear parameter namely the time-of-flight of surface wave is only about 40%. The difference as high as one order of magnitude verifies the high sensitivity of developed air-coupled SHG technique. With consideration of the easily removable characteristic of air-coupled ultrasonic measurements, the developed SHG technique could be promising for the large scale quality control of concrete structures in engineering practice.

This paper investigates the degradation of concrete integrity under the rising temperature using a nonlinear ultrasonic second harmonic generation (SHG) technique based on a fully non-contact approach. The microscopic cracks accumulated during the course of thermal damage is then analytically and experimentally quantified by the elastic wave velocity inversion method and X-ray computed tomography (CT) technique, respectively. The nonlinear parameter calculated by the non-contact SHG technique not only shows a higher sensitivity to the damage growth than traditional macroscopic ultrasonic parameter such as wave velocity, but also presents an excellent correlation with microscopic quantified crack density by showing a proportionally increase with the propagation distance of ultrasonic waves. The experimental findings in this work indicate that the non-contact SHG technique can truly reveal the progressive microscopic cracking of concrete through the macroscopic nondestructive measurements and is suitable for the assessment of globally distributed damage with a high sensitivity and reliability.

3D hierarchical flower-like carbon coated MoO3−x nanosheets (denoted as MoO3−x NS@C) have been successfully fabricated by a simple hydrothermal method. When used as anode for Li-ion batteries, the MoO3−x NS@C electrode exhibits excellent cycle performance and outstanding rate capabilities. The charge capacity can reach 1025 mAh g−1 over 150 cycles, and 62% of the charge capacity is retained when the current density increases to 2000 mA g−1. The improved lithium storage performance of MoO3−x NS@C is attributed to the synergistic effect of oxygen vacancies and the carbon coating, which not only enhance the electric conductivity and Li-ion diffusion coefficient but also lead to superior structural stability and cyclability of the MoO3−x NS@C electrode during repeated lithiation/delithiation process.

Investigations have been performed using microsecond pulsed glow discharge atomic emission spectrometry (GD-AES) to determine the effect of the glow discharge parameters, including applied pulse voltage, pulse width, pulse frequency and gas pressure, on the resolution of depth profiling. The results indicate that a concave crater profile is obtained for low voltage, whereas the curvature is convex for high voltage. The criteria of a flat crater bottom and good depth resolution are fulfilled only with a limited range of voltages at each operating pressure. The results also imply that the pulse frequency and pulse width have little effect on the resolution of depth profiling; thus a wide dynamic range of layers from several nanometers to tens of micrometers can be analyzed by increasing or decreasing the pulse frequency and width. Under the optimized parameters, a thin coating of Cu (50 nm) on steel, an electroplated steel and a computer hard-disk with multiple thin layers were analyzed.

A flexible and free-standing porous carbon nanofibers/selenium composite electrode (Se@PCNFs) is prepared by infiltrating Se into mesoporous carbon nanofibers (PCNFs). The porous carbon with optimized mesopores for accommodating Se can synergistically suppress the active material dissolution and provide mechanical stability needed for the film. The Se@PCNFs electrode exhibits exceptional electrochemical performance for both Li-ion and Na-ion storage. In the case of Li-ion storage, it delivers a reversible capacity of 516 mAh g−1 after 900 cycles without any capacity loss at 0.5 A g−1. Se@PCNFs still delivers a reversible capacity of 306 mAh g−1 at 4 A g−1. While being used in Na-Se batteries, the composite electrode maintains a reversible capacity of 520 mAh g−1 after 80 cycles at 0.05 A g−1 and a rate capability of 230 mAh g−1 at 1 A g−1. The high capacity, good cyclability, and rate capability are attributed to synergistic effects of the uniform distribution of Se in PCNFs and the 3D interconnected PCNFs framework, which could alleviate the shuttle reaction of polyselenides intermediates during cycling and maintain the perfect electrical conductivity throughout the electrode. By rational and delicate design, this type of self-supported electrodes may hold great promise for the development of Li-Se and Na-Se batteries with high power and energy densities.

In this paper, a thin-disk laser with the output power of kW level is demonstrated. The laser used is Nd:YAG laser medium for easiness to reach the threshold power densities of the pump and less heat to dissipate from the crystal. The thin disk of 1 mm thickness with 1.5-at. % Nd doped and a simple 4-pass pump coupling system is designed to fulfill the total absorption of the pump light. 2D-stacks diode array works as the pump source and a conventional optics is used for efficient and uniform pumping.

A diode-laser side-pumped E-O Q-switched TEM00 Nd:YAG slab laser that uses a large N.A. cylindrical lens and a thin slab pumping geometry has been investigated. The pumping scheme has the ability to match well the pump beam to the laser's fundamental transverse mode in two axes. Approximately 1.1 times diffraction limited laser beam is obtained. The slope efficiency is 31% and 18.9% at long-pump and Q-switched operation, respectively.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The diode laser side pumped E-O Q-switch Nd:YAG laser was described that produced energy O.36-mJ/pulse. 7-nspulse width ,pulse repetition rates 50-Hz, TEM00 mode.The laser has a zigzag slab geometry, side pumped with a quasi- cw 15Wdiode bar. We used a 1 .1%Nd:YAG Brewster-cut seven-bounce thin trapezoidal slab that was 1 .2mm thick.Using a cylindrical lens (f=1 .6nim),it made the diode laser couple in the slab. The laser resonator was a plane-concavecavity, radius of mirror curvature was 3m. The cavity length was about 20cm. The plane output mirror transitivity was T=0. 1 . Wedecided to the beam quality M2=1 . 1 . Q-switchlaser slope efficiency was 19%. keyword solid-state lasers, side pumped, diode laser, single transverse mode 1 .INTRODUCTION Diode-laser(LD) pumped solid-state lasers have been one ofthe most interesting and significant developments in laserengineering in recent years1. LD pumping offered high reliability, efficiency and compactness. Side pumping has been togenerate the fundamental transverse mode efficiently2. Recently a side pumping technique used in Q-switch cavity-dumpedand E-O Q-switch laser3 demonstrated efficiency side-pumped operation while still maintaining TEM00 operation. Wereported on a E-O Q-switched laser that used a numerical aperture(NA>1) and short focus length (f=1 .6mm) cylindricallens coupler thin Nd:YAG thin trapezoidal slab and generated 0.36-mJ, 7-ns, TEMo0. pulse repetition rates 50Hz whileusing