Hydrothermal-assisted synthesis of surface aluminum-doped LiCoO2 nanobricks for high-rate lithium-ion batteries

LiCoO₂ nano-particles precursor was synthesized through a mixed-alkalis (LiOH-NaOH) hydrothermal reaction, and finally sintered into LiCoO₂ nanobricks with a sickness of ~300?nm. This LiCoO₂ nanobrick cathode delivered a specific capacity of 131.8 mAh g^?1 at 1?C between 3.0 and 4.2?V and 90% capacity retention after 100 cycles. Those synthesized LiCoO₂ nanobricks were further treated by surface Al³⁺ doping to achieve much enhanced 4.5?V lithium storage capability and cycling stability. EIS results showed the surface Al³⁺ doping operation can signification decrease the charge-transfer resistances of the LiCoO₂ cathodes for both before and after cyclings.     

Piezo-assisted photoelectric catalysis degradation for dyes and antibiotics by Ag dots-modified NaNbO3 powders

NaNbO₃ is explored as a potential candidate for catalysis due to its excellent piezoelectricity. However, its photocatalysis is significantly limited for the inherent characteristics of wide band gap. In this work, NaNbO₃ and Ag dots-modified NaNbO₃ micron-sized powders are prepared and applied in piezo-photocatalysis to explore the coupling effects. The results show that the piezocatalysis degradation efficiency of RhB solution (the initial concentration C₀ = 5 mg/L) reaches 92.3% within 30 min, and the rate constant k is 0.0889 min^?1. The efficiency of piezo-photocatalysis degradation reaches 92.7% in 25 min, and the rate constant k is 0.11 min^?1 for NaNbO₃. The rate constant k of Ag dots-modified NaNbO₃ for piezo-photocatalytic degradation of RhB (C₀ = 5 mg/L) is increased to 0.16314 min^?1. The optical and electrochemical activities of NaNbO₃-0.75hAg are studied to reveal the role of Ag nanoparticles. The band gap of NaNbO₃ is 3.59 eV, which is decreased to 3.36 eV after the modification with Ag dots. The lower band gap means that e^? in the valence band is more easily excited to shift the conduction band, which is beneficial to the photocatalytic reaction process. In addition, NaNbO₃-0.75hAg has a higher photogenerated carrier density, a faster electron-hole pair separation and transfer rate, which are beneficial to the catalytic oxidation process. The work provides a useful means to decease the band gap of NaNbO₃ and achieve outstanding piezo-photocatalysis for degradation of hazardous organic dyes in contaminated water.     

Performance prediction of hard rock Tunnel Boring Machines (TBMs) in difficult ground

Performance prediction of TBMs is an essential part of project scheduling and cost estimation. This process involves a good understanding of the complexities in the site geology, machine specification, and site management. Various approaches have been used over the years to estimate TBM performance in a given ground condition, many of them were successful and within an acceptable range, while some missing the actual machine performance by a notable margin. Experience shows that the best approach for TBM performance prediction is to use various models to examine the range of estimated machine penetration and advance rates and choose a rate that best represents the working conditions that is closest to the setting of the model used for the estimation. This allows the engineers to avoid surprises and to identify the parameters that could dominate machine performance in each case. This paper reviews the existing models for performance prediction of TBMs and some of the ongoing research on developing better models for improved accuracy of performance estimate and increasing TBM utilization.     

Simulation of rate dependent fracture in concrete using an irregular lattice model

An irregular lattice model is used to simulate concrete fracture behavior under dynamic loadings. The numerical approach is based on rigid-body-spring networks, in which a visco-plastic damage model is applied to describe the rate dependency. A direct tensile test is simulated at various strain rates, and the dynamic strength increase is obtained in terms of dynamic increase factor (DIF). The DIFs are compared with a previous experimental and empirical study to calibrate the visco-plastic parameters. Next, a three-point-bending test is conducted numerically under impact and slow loadings, where the mixed-mode fracture is set up with a notch offset from the midspan. The rate-sensitive failure features are shown at the two different loading rates, and the rate effect on the failure mechanism is related with the peak load in the loading history. This study provides qualitative and quantitative understandings of the rate dependent failure behaviors in concrete.     

密闭腔体法准确测量建材氡析出率比较研究

密闭腔体法(closed chamber method)是目前建材氡析出率测量中使用较为广泛的一种方法。使用密闭腔体法测量建材氡析出率,在建材的前处理上,大体上将长方体建材分为完全裸露、包裹留下一面和留下两面三种方法进行测量。本文从建材氡析出率测量的基本理论模型出发,细致比较分析了不同包裹方法测量得到的氡析出率的真实涵义,并结合理论分析和实验验证,提出了合理的修正方法,认为包裹留一面和留两面适合作为建材氡析出率的测量方法。     

认知无线电频谱切换技术研究

认知无线电技术是为提高频谱利用率,解决目前无线频谱资源紧缺问题而提出的,准确快速的频谱切换技术是其实现的关键。论文针对认知无线电技术的频谱切换问题,总结频谱切换的关键技术及研究模型,讨论频谱切换技术面临的挑战,以及频谱切换技术的研究方向。     

浅谈陆相断陷湖盆沉积速率的求取方法——以沾化凹陷沙四段—孔店组为例

沉积速率是指在一定地质历史时期内,表征地层在沉积历史时期的快慢程度[1],其求取方法多种多样,本文对其值的求取采取用地层原始厚度除以该地层沉积期的绝对年龄。沉积速率作为沉积速率剥蚀量计算方法的参数,对恢复区内埋藏史、热史以及生烃史具有重要意义。本文通过深井的地层数据以沾化凹陷渤深5、罗14、桩深1井为例进行了沉积速率的求取并取得了比较精确的成果。     

速率偏频激光陀螺寻北仪标度因数的在线估计

为满足高精度寻北的工程需求,针对激光陀螺内部腔体温度变化和锁区不稳定性等因素会使速率偏频激光陀螺标度因数发生缓慢变化的问题,提出了在线估计标定因数的方法,并研究了速率偏频激光陀螺寻北仪及其标度因数测量误差.首先,通过标度因数实验研究其变化规律;然后,仿真分析了激光陀螺标度因数测量误差对寻北精度的影响;最后,根据陀螺测量...     

Stability of Polymer Electrolyte Membranes In Fuel Cells: Initial Attempts To Bridge Physical And Chemical Degradation Modes

In recent years, research on coupled degradation of Nafion^® membrane in polymer electrolyte fuel cell has generated huge interest among the scientific community. The coupled phenomenon behind the premature failure of fuel cell membranes in terms of its degradation is not well established. As the researches on this are in its adolescence, we try to provide some significant answers to the degradation phenomenon in terms of mechanically stimulated chemical degradation of the membrane. While the basic concept heavily relies on accurately modeling the membrane for its mechanical response to obtain molecular chain stretch, the results are utilized by the modified chemical rate equation for unzipping degradation mechanism. This article addresses significant degradation issues such as localized membrane thinning and pinhole formation, and inhomogeneous damage patterns in membrane electrode assembly in terms of mechanically induced accelerated chemical degradation of the membrane.