Zero-voltage-switching buck converter with low-voltage stress using coupled inductor

This study presents a new zero-voltage-switching (ZVS) buck converter. The proposed converter utilises a coupled inductor to implement the output filter inductor as well as the auxiliary inductor which is commonly employed to realise ZVS for switches. Additional magnetic core for the auxiliary inductor in traditional ZVS converters is eliminated and hence reduced cost is achieved. Moreover, thanks to the series connection between the input and output, the switch voltage stress in the steady state is reduced and thus the ZVS operation can be easier achieved. Then the leakage inductor current circulating in the auxiliary switch is decreased, contributing to reduced conduction losses. In particular, low-voltage rating devices with low on-state resistance can be adopted to further improve efficiency in applications with non-zero output voltage all the time, such as the battery charger. Furthermore, the reverse-recovery problem of the diode is significantly alleviated by the leakage inductor of coupled inductor. In the study, operation principle and steady-state analysis of the proposed converter are presented in detail. Meanwhile, design considerations are given to obtain circuit parameters. Finally, simulations and experiments on a 200 W prototype circuit validate the advantages and effectiveness of the proposed converter

An Overview of Recent Development in Composite Catalysts from Porous Materials for Various Reactions and Processes

Catalysts are important to the chemical industry and environmental remediation due to their effective conversion of one chemical into another. Among them, composite catalysts have attracted continuous attention during the past decades. Nowadays, composite catalysts are being used more and more to meet the practical catalytic performance requirements in the chemical industry of high activity, high selectivity and good stability. In this paper, we reviewed our recent work on development of composite catalysts, mainly focusing on the composite catalysts obtained from porous materials such as zeolites, mesoporous materials, carbon nanotubes (CNT), etc. Six types of porous composite catalysts are discussed, including amorphous oxide modified zeolite composite catalysts, zeolite composites prepared by co-crystallization or overgrowth, hierarchical porous catalysts, host-guest porous composites, inorganic and organic mesoporous composite catalysts, and polymer/CNT composite catalysts

Experimental study on bending mechanical properties of moso bamboo

Moso bamboo, as an environmentally friendly material, has become a research hotspot in civil engineering circles, and its good mechanical properties make it have great potential in civil engineering applications. To take full advantage of moso bamboo, a series of bending tests were carried out on bamboo pipes (RBP), hollow bamboo pipes (HBP, without bamboo membrane) and bamboo pipes with concrete(BPC), and analyzed such as bending strength, flexural bearing capacity, deformation law, failure characteristics and other test results. The results showed that the smaller the diameter of moso bamboo is, the greater the bending strength and elastic modulus are; the maximum strain of BPC is 2.5 times the HBP, the distribution of strain along cross section is linear; RBP, HBP, and BPC show different failure pattern; there is a little difference between RBP and HBP that come from the same moso bamboo and have a similar diameter in limit capacity, bending strength, and elastic modulus; the flexural bearing capacity of BPC is 2.4 times the HBP, the bending strength is 1.7 times, the composite structure is effectively enhanced by concrete. The test results can provide references for the application of bamboo in landslide treatment, the supporting structure of the foundation, and other engineering

Water Transfer Characteristics during Methane Hydrate Formation Processes in Layered Media

Gas hydrate formation processes in porous media are always accompanied by water transfer. To study the transfer characteristics comprehensively, two kinds of layered media consisting of coarse sand and loess were used to form methane hydrate in them. An apparatus with three PF-meter sensors detecting water content and temperature changes in media during the formation processes was applied to study the water transfer characteristics. It was experimentally observed that the hydrate formation configurations in different layered media were similar; however, the water transfer characteristics and water conversion ratios were different

An Efficient V2I Authentication Scheme for VANETs

The advent of intelligent transportation system has a crucial impact on the traffic safety and efficiency. To cope with security issues such as spoofing attack and forgery attack, many authentication schemes for vehicular ad hoc networks (VANETs) have been developed, which are based on the hypothesis that secret keys are kept perfectly secure. However, key exposure is inevitable on account of the openness of VANET environment. To address this problem, key insulation is introduced in our proposed scheme. With a helper device, vehicles could periodically update their own secret keys. In this way, the forward and backward secrecy has been achieved. In addition, the elliptic curve operations have been integrated to improve the performance. The random oracle model is adopted to prove the security of the proposed scheme, and the experiment has been conducted to demonstrate the comparison between our scheme and the existing similar schemes

Research on Mechanical Characteristics of Slope Reinforcement by Spatial Arc Crown Beam Composite Supporting Structure

To effectively optimize the mechanical behavior of a traditional anti-slide pile and reduce environmental destruction, a new method for slope reinforcement by a spatial arc crown beam composite supporting structure was proposed. First, a numerical model was validated through lab-scale model test data obtained herein, and then a full-scale numerical model was created for an in-depth understanding of the distribution regularity of displacement along the pile, the soil pressure, the crown beam stiffness, and so on. The results demonstrated that: (1) The spatial arc crown beam is simplified to a two-hinged arch, and the maximum value of the bending moment in the arc crown beam is about one-third of the straight crown beam through theoretical calculation. (2) The spatial arc crown beam redistributes the load sharing among different piles, and the extreme bending moment of other piles varies within 10% along the downhill direction except for the piles at the slope foot. (3) Bending moments are close to zero at the pile end, and the anti-slide pile can be simplified as a vertical beam with one end fixed and the other end hinged. (4) The axial force in the spatial arc crown beam is always presented as pressure, so the crown beam can make full utilization of the compression resistance of concrete. (5) The distribution characteristic of soil pressure in front of the pile at the arch foot is different from that in other positions, and the stable soil at the slope foot provides greater soil resistance for anti-piles. (6) As the crown beam stiffness is above five times the reference value, the axial force of the crown beam tends to be stable, and as the crown beam stiffness increases continually, the maximum value of My is −1013.13 kN·m, and the constraining effect of the crown beam is gradually weakened

An Experimental Study on the Ecological Support Model of Dentate Row Piles

Bamboo is highly renewable and biodegradable with good short-term strength, which meets the requirement for temporal support structures in shallow foundation pits. Based on this, we conducted a laboratory model test on the dentate bamboo micropile support structure combined with environmentally friendly building materials and new type of piles, to explore the stress characteristics, stress change regularity, and the support effect of the system in soft soil foundation pits. The results show that the earth pressure on the pile sides above the excavation surface gradually decreases with an increase in the excavation depth. The bending deformation of the bamboo pile was also significant. The results also show that the earth pressure and the pile strain below the excavation surface change slightly during the excavation process. When the short sides of the foundation pit were loaded, the highest strain was recorded in the piles 4 and 11. A maximum strain of 358.93 με was recorded, and the maximum displacement of the pile in the top part was obtained to be only 2.14 mm. The most subsidence of dentate pile obtained is only 1.88 mm, whereas that of the single-row pile is 2.35 mm. Compared to the traditional single-row pile, the dentate piles can effectively reduce the horizontal deformation as well as the surface subsidence effectively. They can also support more external lateral load, and hence maintain the foundation stability and give better support. The results provide a theoretical basis for ecological bamboo support technology and have great value to be promoted

Application of

In this paper, a technique to determine complicated stress intensity factors on three-dimensional components, which based on the conservation law and the elementary mechanics is proposed, it only needs the geometric relationship between multiple singular stress fields from the crack section, and obtaind the relationship between the stress at different crack tips. In the expression of the stress intensity factor K, K is proportional to the stress σ at the crack tip, and we can get the supplementary equation of between different stress fields K according to the ratio of the stress at the crack tip, then use the J-integral method to calculate the stress intensity factors of different stress fields. In order to verify the feasibility of this method, a cracked R-fluted shells model was constructed. Under the action of the bending moment, the corner crack propagation is simulated through the reserved corner crack, and two crack tips with different stress fields are generated during the simulation. The experimental result indicates that the proposed method is effective for cracked R-fluted shells. It is also shown that the method has universal applicability for solving complex stress intensity factors on three-dimensional components

Experimental Study on the Microstructure and Expansion Characteristics of Paleosol Based on Spectral Scanning

To investigate the microstructure of paleosol and its expansion characteristics, the paleosol of the Zaosheng #3 tunnel of the Yinxi high-speed railway was studied. Based on X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), nuclear magnetic resonance (NMR), and scanning electron microscopy techniques (SEM), the microstructure of the paleosol was analyzed in terms of the mineral composition, formation elements, pore structure, and particle morphology. Five groups of undisturbed and remolded soils with different moisture contents were tested for the unloaded expansion rate and loaded expansion rate. The results show that the mineral components of the paleosol are mainly quartz, potash feldspar, calcite, and hematite, with the highest-content-component quartz accounting for 45.4% of the total content; the clay mineral composition of the paleosol has the highest content of montmorillonite at 12.3%. The elemental composition of the paleosol is dominated by Al, Si, Ca, and Fe, which form expansive mineral components such as quartz and montmorillonite, creating inherent conditions for expansibility of the paleosol. The T2 distribution curves of the undisturbed and remolded paleosol are composed of three peaks. The pore distribution of paleosol mainly includes medium pores, followed by large pores, and the contents of small pores and superlarge pores are very small. In terms of particle contact, the undisturbed soil is mostly in the form of “surface-surface” and “surface-edge” contact, and the remolded soil is mainly in the form of “point-surface” and “point-point” contact. The unloaded expansion rate of remolded soil is approximately twice that of undisturbed soil. The rate of loaded expansion of both soils decreases with increasing moisture content