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Thermal oxidation and hydrogen annealing were applied on a 100 μm thick Al-doped p-type 4H-SiC epitaxial wafer to modulate the minority carrier lifetime, which was investigated by microwave photoconductive decay (μ-PCD). The minority carrier lifetime decreased after each thermal oxidation. On the contrary, with the hydrogen annealing time increasing to 3 hours, the minority carrier lifetime increased from 1.1 μs (as-grown) to 3.14 μs and then saturated after the annealing time reached 4 hours. The increase of surface roughness from 0.236 nm to 0.316 nm may also be one of the reasons for limiting the further improvement of the minority carrier lifetimes. Moreover, the whole wafer mappings of minority carrier lifetimes before and after hydrogen annealing were measured and discussed. The average minority carrier lifetime was up to 1.94 μs and non-uniformity of carrier lifetime reached 38% after 4-hour hydrogen annealing. The increasing minority carrier lifetimes could be attributed to the double mechanisms of excess carbon atoms diffusion caused by selective etching of Si atoms and passivation of deep-level defects by hydrogen atoms.

Recently, we have successfully realized the catalytic synthesis of nanodiamond (ND) by embedding the Fe catalyst into carbide under high stress, followed by chlorine-etching at atmospheric pressure. In this work, we selected Fe, Co and Ni as the catalyst, and TiC as the precursor, aiming at investigating the influence of the catalyst type on the synthesis of NDs. The results have shown that all the three catalysts can catalyze the synthesis of ND structure, where various types of NDs have been observed. Furthermore, the crystal type and plasticity of the catalyst may have an important influence on the type and size of the resultant ND. In the case of Fe and Ni as the catalyst, both of which have a face centered cubic crystal structure, the types of NDs obtained are mainly C-type and R-type but only a few H-type. However, when the Co with a close-packed hexagonal crystal structure is used as the catalyst, more H-type NDs can be catalytically synthesized. Moreover, more small-sized NDs have been catalytically synthesized by Co, which may be ascribed to the worse plasticity of Co by comparison to Fe and Ni.

This Aiming at the problem of horizontal vibration of high-speed elevators caused by the guide rail excitation, firstly, considering the nonlinear characteristics of the spring rigidity and damping of the guide shoe system, a four-degree-of-freedom high-speed elevator nonlinear horizontal vibration model is established. Secondly, the state equation of horizontal vibration of high-speed elevator is derived, and the system state is processed by Taylor expansion. The quadratic performance index of predictive control is introduced, and the active control law with analytic form is solved by optimizing the performance index. Finally, the simulation using MATLAB verifies the correctness of the model. By further solving the control law and simulation, the results prove that predictive control can effectively reduce the horizontal vibration of high-speed elevators.

With the increase of building height, more and more high-speed elevators are applied to high-rise buildings in order to improve the transportation efficiency of people in buildings. Compared with the medium and low speed elevators, the airflow in the shaft is more severe when the high-speed elevator car is running in the narrow and long shaft, and the influence of aerodynamic force and aerodynamic noise is more obvious. In order to explore the aerodynamic characteristics of the high-speed movement of the elevator car and the airflow law in the shaft, and further optimize the aerodynamic parameters of the high-speed elevator shaft system, a full-scale three-dimensional model of the shaft with different blocking ratio is established and numerically simulated. Through the analysis of the calculation results of different blockage ratio of the shaft model, it is found that the greater the blockage ratio is, the greater the resistance of the car operation is, and the airflow disturbance behind the car movement is more severe than that in the front. The calculation results provide a reference for further exploring the airflow flow law in the high-speed elevator shaft.

In the real service environment of high-speed traction elevator, the horizontal sway of towing wire rope caused by the center of gravity deviation and airflow disturbance seriously affects the comfort of passengers in the elevator. In view of this problem, this paper first establishes the equivalent model of the flexible traction wire rope of high-speed elevator. Secondly, based on the energy method, the lateral stiffness calculation formula of the towing wire ropes is derived, and then compares the stiffness calculation formula derived from the classical stiffness calculation formula to verify the correctness of the proposed stiffness calculation formula. Last but not least, In MATLAB, the regularity of tension force and traction wire rope lift length on the minimum lateral stiffness value and minimum stiffness position is explored. The results show that the tension force is positively correlated with the minimum stiffness value, negatively related to the minimum stiffness position, and the lifting length of the traction wire rope is negatively related to the minimum stiffness value, and the minimum stiffness position is positively correlated.

The development of technical strategies for synthesizing nanodiamond (ND) under moderate conditions is still an attractive and challenging issue. Herein, an attempt has been made to investigate the effect of the Fe-introduction mode on the catalytic synthesis of ND during the chlorination of vanadium carbide (VC) at ambient pressure. The results show that when Fe powder as a catalyst is adhered on the surface of the VC particle, the resultant carbide-derived carbon (CDC) by chlorinating VC at 800 °C behaves as a remarkably higher structural ordering. However, as the Fe powder is enclosed within the interior of VC particles, the structural ordering of the CDC obtained at the same chlorination temperature becomes greatly lower, and more interestingly, ND structures can be observed in the prepared CDC. This suggests that the catalytic synthesis of ND during VC chlorination at ambient pressure is heavily dependent upon the Fe-introduction mode.

The development of effective strategies for the massive production of layer-number tunable graphene is of great importance to satisfy the requirements in versatile applications such as energy storage, thermal management, photocatalysis. However, how to prepare the layer-tunable graphene by a simple and efficient way is still a great challenge. Herein, an attempt has been made to exfoliate graphite into layer-tunable graphene by simply soaking the graphite in a binary-component solution composed of H2SO4 and (NH4)2S2O8. In this one-step method, we demonstrate that the layer-number for the as-prepared graphene can be significantly reduced by increasing the exfoliating temperature. An average thickness of ∼20, ∼10, and ∼3 atomic layers can be obtained for the graphene samples exfoliated at the temperature of 30 °C, 60 °C, and 90 °C, respectively. Meanwhile, higher exfoliating temperature not only facilitates the higher efficiency in the exfoliation of graphite, but also achieves a superior conductivity for the prepared graphene. We have demonstrated for the first time that controlling in a sole factor of temperature can effectively tune the layer-number of graphene by a one-step chemical exfoliation method, which will find its great potential in the practical application where the designated property of graphene is required.

Night flush cooling is an effective passive strategy to condition spaces and provide larger capacity to store heat. A common technique to quantify the benefit from this cooling strategy is using building energy simulation (BES) modelling, which, however, is weak in capturing the airflow patterns and convective heat transfer under the complex urban contexts. Therefore, dynamic coupling techniques of BES to computational fluid dynamics (CFD) are often used to improve the simulation performance of the night flush cooling strategies. Nonetheless, dynamic coupling techniques always encounter a high computational cost to achieve accurate CFD calculations for naturally ventilated scenarios, as high-resolution grids are required to be prepared. Therefore, a framework of integration of a fine-resolution CFD grid (CFDf), a coarse-resolution CFD grid (CFDc) and BES is proposed in this work to study night-flush cooling. In this framework, the CFDf domain performs as the off-line module that generates the boundary conditions for the CFDc domain at its openings before the start of the iterative calculations. CFDc and BES domains are then performing a fully dynamic external coupling to achieve a convergence for the energy simulation using the updated convective heat transfer coefficient (CHTC) profiles at the exterior surfaces. A case study is investigated for a simple urban morphology in Los Angeles on a typical hot day. The results highlight an improvement in representation of the neighbourhood effect in energy calculations obtained in a feasible calculation run-time.

The relationship between network capability and service performance is studied by introducing structural embeddedness in the servitization manufacturing enterprises, and the main contribution of network capability to service performance and the mediating effect of structural embeddedness are analyzed respectively. An empirical study is presented by using factor analysis, correlation analysis and regression method to analyze the sample data collected from 236 servitization manufacturing enterprises. It can be shown that network capability is beneficial to service performance and significantly positive correlated with structural embeddedness, structural embeddedness has a significantly positive impact on service performance and plays a partial mediating role in the relationship between network capability and service performance.

The piston wind will be produced when the car runs at high speed in the narrow and long hoistway, which will produce aerodynamic noise with the car enclosure and the hoistway walls, thus affecting ride comfort. In order to put forward better noise reduction measures, a piston wind model of super high-speed elevator with ventilation holes during the whole operation process was established firstly in this paper. Then, based on this theoretical model, the influence of the variation of ventilation-hole area, hoistway blockage ratio and car length on the piston wind was analysed separately. The analysis proved that the larger the area of ventilation holes, the more obvious the weakening of piston wind was when the building code permits. With the increase of blockage ratio, the intensity of piston wind increases obviously, but the duration of maximum piston wind does not change obviously. As the length of the car increases, there is no significant change in the movement of the piston wind, and this small change can be ignored in engineering applications.

Aiming at the problem of transverse vibration of high-speed elevator caused by surface roughness excitation of guide rail and relative motion between car and car frame, firstly, this paper establishes an eight-degree-of-freedom active control model for the transverse vibration of the high-speed elevator separated of car from the car frame. Secondly, the transverse vibration state equation of the high-speed elevator is derived. The H 2 norm is used to minimize the vibration acceleration of the car system. Based on Linear matrix inequality (LMI) optimization technology, a robust controller for the high-speed elevator is designed. Finally, the robust controller is solved by MATLAB and its simulation analysis is carried out. The results show that the vibration of the car and the car frame is inconsistent in actual operation. At the same time, the simulation results also show that the root mean square value, mean value and maximum value of the acceleration of the transverse vibration of the car and the car frame are reduced by more than 19% after using the robust controller. Therefore, the robust controller designed in this paper can effectively suppress the transverse vibration of the vibration car system.

With the increase of elevator running speed, the influence of aerodynamic force on elevator becomes more and more obvious, and the impact is also increasing gradually. In this paper, the Computational Fluid Dynamic numerical simulation method is used to simulate and analyse the aerodynamic characteristics of elevator car under the influence of different operating speed and distance from side of car to hoistway wall by establishing full-scale model of elevator and hoistway. The results show that when the car is in a symmetrical position, the aerodynamic characteristics on both sides always show obvious symmetry. With the decrease of distance from side of car to hoistway wall and the operating speed of the car, the flow field around the car changes intensified, and the aerodynamic forces on the side of the car will also increase significantly.

In order to develop energy storage devices with high power performance, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate a highly conductive graphene nanosheet/nanometer-sized carbide-derived carbon framework (hcGNS/nCDC). In this architecture, nCDC possesses short transport paths for electrolyte ions, thus ensuring the rapid ions transportation. The excellent electrical conductivity of hcGNS can reduce the electrode internal resistance for the supercapacitor and thus endows the hcGNS/nCDC composite electrodes with excellent electronic transportation performance. Electrochemical measurements show that the cyclic voltammogram of hcGNS/nCDC can maintain a rectangular-like shape with the increase of the scan rate from 5 mV s-1 to 20 V s-1, and the specific capacitance retention is up to 51% even at a high scan rate of 20 V s-1, suggesting ultrahigh power performance, which, to the best of our knowledge, is among the best power performances reported so far for the carbon materials. Furthermore, the hcGNS/nCDC composite also shows an excellent cycling stability (no drop in its capacitance occurs even after 10000 cycles). This work demonstrates the advantage in the ultrahigh power performance for the framework having both short transport pathways for electrolyte ions and high electrical conductivity.

We propose a novel and facile synthesis approach to a porous carbon/graphene composite. Graphene is obtained from room-temperature expanded graphite (RTEG), not involving the use of graphite oxide (GO). Porous carbon is acquired by carbonization and KOH-activation of polyvinylpyrrolidone (PVP), which is used to exfoliate RTEG into graphene and inhibit the restacking of the resultant graphene in the present work. The prepared porous carbon/graphene composite has a high specific surface area (SSA) (3008 m2 g−1) and a hierarchical micro- and meso- pore structure (dominant pores in the range of 1–5 nm). Electrochemical measurement demonstrates that the as-prepared porous carbon/graphene composite can deliver an outstanding specific capacitance of up to 340 F g−1 at 5 mV s−1 in 6 M KOH electrolyte. This specific capacitance is among the highest reported so far for porous carbon/graphene materials. Moreover, the prepared composite as an electrode material also exhibits excellent cycling stability (94.4% capacitance retention over 10 000 cycles). The as-fabricated symmetrical supercapacitor exhibits a high energy density of 10.9 W h kg−1 (based on total mass of electrode materials) and an outstanding energy density retention, even at high power density. Compared with conventional preparation routes for porous carbon/graphene composites, the present approach is significantly simple, convenient and cost-effective, which will make it more competent in the development of electrode materials for high-performance supercapacitors.