Search

Preparation of porous TiAl-based intermetallics with aligned and elongated pores by freeze-casting was investigated. Engineering Ti−43Al−9V−1Y powder (D50=50 μm), carboxymethyl cellulose, and guar gum were used to prepare the aqueous-based slurries for freeze-casting. Results showed that the porous TiAl was obtained by using a freezing temperature of −5 °C and the pore structure was tailored by varying the particle content of slurry. The total porosity reduced from 81% to 62% and the aligned pore width dropped from approximately 500 to around 270 μm, with increasing the particle content from 10 to 30 vol.%. Furthermore, the compressive strength along the aligned pores increased from 16 to 120 MPa with the reduction of porosity. The effective thermal conductivities of porous TiAl were lower than 1.81 W/(m·K) and showed anisotropic property with respect to the pore orientation.

Electric vehicles (EVs) is attracting great attentions worldwide due to its significant effect on reduction of oil dependency and carbon emissions, which are the critical issues faced by conventional vehicles. However, there are also problems for EVs, one of which is range anxiety. In order to alleviate range anxiety of drivers, it is very important to predict the remaining driving range accurately. This paper aims to improve the accuracy of the remaining driving range estimation using Back Propagation Neural Network method. The data used to train the model was collected from six operating vehicles, which can reflect the real-world driving condition. The results show that the established model significantly improved the accuracy of the remaining driving range estimation.

A pattern-reconfigurable patch antenna with nine beam directions based on the complementary split-ring resonator (CSRR) loaded ground is proposed. The antenna consists of a coaxial feed rectangular patch on the top layer and a ground plane loaded with four CSRRs on the bottom layer. Two p-i-n diodes are installed on the stub of every CSRR. By changing the states of the p-i-n diodes, the main radiation direction can be switched both in the E-plane and H-plane. The operation principle of the beam switching by loading CSRRs on the ground is discussed. The prototype is fabricated with p-i-n diodes and bias circuit. The measured common impedance bandwidth of |S 11 | less than -10 dB is from 2.42 to 2.48 GHz. The 3-dB beamwidth covers the elevation angles from 0° to more than 60° and full azimuth angles. The antenna has a compact size of 0.82 λ 0 × 0.78 λ 0 , which has the potential to be used in the array design.

In this paper, a printed and miniaturized planar slot antenna is designed, which has the function of pattern and frequency reconfigurability. The antenna structure consists of two semi-circular slots, a CPW open ended branch and a CPW feedline. By changing the states of switches, the antenna can operate among the three frequency reconfigurable states of low band, high band and dual band. The low and high band cover 2.23-3.49GHz and 5.43-5.94 GHz, respectively. The null direction of radiation pattern at high frequency band can also be steered by changing the states of the switches installed in the semi-circular slot. When the antenna operates in 5.8 GHz. The antenna does not have any additional matching circuit, which brings simple structure and wideband.

As one of the main hazard in the downhole operation, the coal dust not only threats the safety of underground workplaces, but also affects the health of workers. In this paper, we elaborate the current situation of dust in the full-mechanized work face and corresponding preventive measures, design an air curtain dust-collecting device and analyzes its working principle. In order to study the effect of dust prevention of the proposed air curtain dust-collecting device, we studied the movement rule of wind and dust by software of FLUENT. The simulation result shows that the air curtain can control the dust concentration well in the full-mechanized work face. Most of the dust generated during tunneling operations have been cut off in the driver’s front air curtain, and this helps us to effectively avoid the dust spreading to the side of the operating driver.

A high gain and broadband Vivaldi antenna with end-fire and equal beamwidth radiation pattern at Ka band is presented in this paper. The Vivaldi slot is fed by the microstrip line-to-substrate integrated waveguide (SIW) transformer. The SIW transmission performance is enhanced by another row of metal vias beside the original one. On both sides of the Vivaldi conductor planes, 8 parallel slots with gradually increasing length are etched to improve the front-to-back ratios. Under the microstrip feed line, three pairs of split ring resonators (SRRs) are etched on the ground to suppress the secondary harmonic. In order to improve the antenna gain and obtain the equal E- and H-plane beamwidths, the special designed zero-epsilon metamaterial (ZEM) units are loaded on the Vivaldi slot with a maximum gain increment of 3.4dB being obtained. The antenna exhibits a broad bandwidth of 38.5% at 35GHz ranging from 26.5GHz to 40GHz with the reflection coefficient less than −10dB, and the gain varying between 9.7dBi and 12.2dBi. The proposed antenna is fabricated and measured to validate the design. The measured results are in good agreement with the simulated ones. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2337–2341, 2016

In the northern part of China, the heating system of the Chinesekangoccupies a significant proportion of usage, particularly during the winter. To achieve better heating effect, this article explored the wind tunnel (commonly known as the “dog hole”) of the Chinesekangin the Northern area. The paper conducted three experiments, established a two-dimensional mathematical model on the flow of high temperature gas in the chimney, utilized the FLUENT software to simulate the flow, and analyzed the inlet flow of the chimney flue and effect of wind tunnel on the heating system of Chinesekang. Wind tunnel was found to prevent natural reversed wind effectively and reduce the influence of outside wind.

A wideband printed tapered-slot antenna with pattern reconfigurability is proposed. The antenna consists of four tapered slots, a reconfigurable microstrip-to-slotline transition, and four p-i-n diodes. With a suitable arrangement of bias voltages, four endfire radiation patterns are realized with a simple bias circuit. The measured relative impedance bandwidth of $\vert{ S}_{11}\vert$ less than ${-} 10~\hbox{dB}$ is 71.3%, which is from 1.57 to 3.31 GHz in all operation modes. The gains for four directions are all higher than 6.4 dBi at the center frequency of 2.4 GHz. The measured and simulated results agree with each other well. The proposed antenna has good performances at four reconfigurable directions in a wide band.

In order to study the coupling problem between methane drainage and spontaneous combustion of residual coal in the collapsed zone after mining ignitable coal seams with high methane, we have analyzed the effects of different methane drainage modes on spontaneous combustion of residual coal through numerical simulation. The results show that deep and large flux methane drainage modes increases the air leakage from work faces to the goaf and formed new spontaneous combustion zones induced by drainage near vents, which increases the risk of self-ignition of coal—reducing the self-ignition period and enlarging the scale of self-ignition. The spontaneous upstream combustion oxidation of the main fire zone can be suppressed when both drainage and nitrogen injection were adopted. Our research results provide an effective technical measure and theoretical basis to determine the best methane drainage scheme and drainage parameters.

Respiration particles can be collected into a dust catcher by an inside inhaling and outside pressing particle collector. The work environment of the grab operator in tunneling mining was improved when a dust catcher is placed before the working face of the grab operator. The particle movement was affected by the gas flow. The flow field inside and outside the dust collector was simulated. The effect of the operating parameter was analyzed. The numerical results show a good approach to predict the gas flow and particle distribution in the inside and outside of the particle collector.

In this paper a novel planar beam steering antenna controlled by reactive loads is proposed and designed based on the principle of electrically steerable parasitic array radiator antenna (ESPAR). The antenna prototype is designed using HFSS and the reactance values are optimized by the differential evolutionary (DE) algorithm. The main beam can be steered from -34° to 40° in the xoy plane by controlling the value of the loaded reactance. The frequency range of each state with S11 below -10dB is from 5.7GHz to 6.1GHz while the gain is from 3.5dBi to 4.9dBi.