波束倾斜的高次模谐振微带天线

本文设计了一款波束倾斜的高次模谐振微带天线。结合差分馈电和电流干扰技术,使工作在高次谐振模式的矩形贴片,保持均匀的电流分布。通过在天线正上方添加具有高透射特性、相位渐变的电磁表面,对电磁波透射相位进行控制,实现指定的波束偏转。最终设计出波束在E面偏转10°的TM90模微带天线,仿真峰值增益达到16.2dBi,工作带宽为7.2%。实测天线峰值增益为15.4dBi,E面副瓣电平低于-15.8dB,交叉极化低于-26dB,工作带宽为5.4%。

Limb symmetry index in competitive alpine ski racers:Reference values and injury risk identification according to age-related performance levels

Purpose： The aims of this study were to assess differences of limb symmetry index （LSI） in strength- and coordination-related tasks between high-level, competitive, noninjured ski racers of different age-related performance levels and to prospectively assess limb differences as a possible risk factor for traumatic and overuse injury in youth ski racers. Methods： The study （Study 1） included 285 high-level competitive ski racers （125 females, 160 males） of 3 age-related performance levels and based on the school system： 95 youth （10-14 years, secondary modem school）, 107 adolescent （15-19 years, grammar school）, and 83 elite athletes （20-34 years）. To investigate the second aim （Study 2）, 67 of the 95 youth athletes were included and any traumatic or overuse injuries were prospectively recorded over 2 seasons. All athletes performed 4 unilateral tests （strength related： one-leg counter movement jump （OL-CMJ） and one-leg isometric/isokinetic press strength test （OL-ILS）; coordination related： one-leg stability test （OL-ST） and one-leg speedy jump test （OL-SJ））. The LSI was calculated by dividing the dominant leg by the nondominant leg and multiplying by 100. Kruskal-Wallis H tests and binary logistic regression analyses were conducted. Results： There were significant differences between the LSI of the 3 age-related performance-level groups only in the strength-related tests： the OL-CMJ （X^2（2, 285） = 9.09; p = 0.01） and the OL-ILS （X^2（2,285） = 14.79; p 〈 0.01）. The LSI for OL-ILS was found to be a significant risk factor for traumatic injury in youth ski racers （Wald = 7.08; p 〈 0.01）. No significant risk factors were found for overuse injuries. Conclusion： Younger athletes display slightly greater LSI values only in the strength-related tests. The cut-off value of limb differences of 〈 10% for return to sport decisions seems to be appropriate for elite athletes, but for youth and adolescent athletes it has to be critically discussed. It seems to be necessary to define thresholds based on specific performance tasks （strength vs. coordination related） rather than on generalizations, and age-related performance levels must be considered. Limb differences in unilateral leg extension strength represent a significant injury risk factor in youth ski racers.2018 Published by Elsevier B.V. on behalf of Shanghai University of Sport. This is an open access article under the CC BY-NC-ND license. （http：//creativecommons.org/licenses/by-nc-nd/4.0/）.

Overcharge performance of LiMn_2O_4/graphite battery with large capacity

The LiMn2O4/grapbite battery was fabricated and its 3 C/10 V overcharge performance was studied. Spinel LiMn2O4 was synthesized by solid-state method and 325680-type size full battery was fabricated. The structure and morphology of the powders were characterized by XRD and SEM technique, respectively. The battery explodes after 3 C/10 V overcharged test, and surface temperature of the battery case arrives at 290 ℃ in 12 s after exploding. Black air is given out with blast. Carbon, MnO, and Li2CO3 are observed in the exploded powders. The cathode electrode remains spinel structure with 5.0 V charged. Cracks in the cathode electrode particles are detected with the increase of voltage by SEM technique. The 5.0 V charged electrode can decompose into Mn3O4 at 400 ℃. It is demonstrated that the decomposition of 5.0 V charged electrode can be promoted and Mn^4＋ can be deoxidized to Mn^2＋ by carbon and electrolyte through the simulation of blast process.

High Temperature Corrosion of Water Wall Materials T23 and T24 in Simulated Furnace Atmospheres

Candidate materials for water wall of supercritical and ultra-supercritical utility boilers,T23 and T24,were chosen as the experimental samples and exposed to oxidizing atmosphere,reducing atmosphere and oxidizing/reducing alternating atmosphere separately.The corrosion temperature was 450-550?C.The effects of oxygen con-tent and temperature on the corrosion in reducing atmosphere and alternating atmosphere were investigated.The scanning electron microscope(SEM) and energy dispersive spectrometer(EDS) were used to examine the corroded samples.The results show that the corrosion kinetics of T23 and T24 can be described by the double logarithmic equation and parabolic equation respectively.To describe the corrosion of materials accurately it is not sufficient to analyze the macro-mass gain and the macro-thickness of the corroded layer only,but the EDS should be applied to examine the migration depth of corrosive elements O and S.It is revealed that the corrosion becomes more severe when H2S is present in the corrosive gas.S is more active than O,and Cr can reduce the migration of oxygen but not S.The combination corrosion of S and O and pure [S] has a stronger corrodibility than pure H2S.T24 suffers the most severe corrosion at oxygen content of 0.8%.Corrosion is aggravated when the corrosion temperature is above 450 ℃ in the alternating atmosphere.T23 has better corrosion resistance than T24 and W contributes a lot to the corrosion resistance of T23.

The Double Excitation： A Solution to Improve Energetic Performances of High Power Synchronous Machines

DFSM （doubly fed synchronous machine） presents several advantages such as efficiency improvement, weight reduction and increase of the utilization factor （kW/kg）. In this paper the authors focus on impact of the DFSM on the efficiency and machine weight in comparison to conventional synchronous generator with wound rotor. Different topologies of DFSM are briefly described and the different methods and models for performances prediction are presented.

Temperature-resistant and flexible supercapacitors based on 10-inch wafer-scale nanocarbon films

Most of the supercapacitors reported in literatures showed little or no flexibility in the working temperature around 150℃. However, the supercapacitors are generally exposed under complex system or extreme temperature, such as electric vehicles and extremely cold area. Herein, we successfully fabricated a large-scale robust nanocarbon hybrid film consisting of reduced graphene oxide (rGO), carbon nanotubes (CNTs) and MnOx nano-flowers with the size up to 550 cm^2. The mechanical properties of the hybrid films depend on the ratio o f CNTs. The supercapacitors prepared with the hybrid films exhibit high flexibility and keep their performances in a temperature range from - 20 to 200℃. In addition, the devices display remarkable electrochemical and deformation stability at extrem e temperature. This strategy has a potential for the more efficient preparation of flexible electrode materials.

Investigate the nonuniformity of low-energy electron beam with large cross-sections

Over the past decades, low-energy electron accelerators have been used worldwide for surface curing and sterilization. The beam nonuniformity is an important parameter of the low-energy electron beam with large cross-sections. A simple and accurate measurement system of nonuniformity for the low-energy electron beam with large cross-sections was developed. The main concept consists in the measurement of nonuniformity, which is realized by using a linear actuator to drive two scanning wires through the beam's cross-sections at a fixed speed. The beam distribution can be obtained by sending/collecting the current signals to/from the Data Acquisition (DAQ) software on a laptop by a USB DAQ card. This device is very convenient for the performance testing of a new accelerator at the manufacturer's site. The distribution of the homemade low voltage electron accelerator EBS-300-50 was measured and evaluated.