Enhanced graphitic domains of unreduced graphene oxide and the interplay of hydration behaviour and catalytic activity

Previous studies indicate that the properties of graphene oxide (GO) can be significantly improved by enhancing its graphitic domain size through thermal diffusion and clustering of functional groups. Remarkably, this transition takes place below the decomposition temperature of the functional groups and thus allows fine tuning of graphitic domains without compromising with the functionality of GO. By studying the transformation of GO under mild thermal treatment, we directly observe this size enhancement of graphitic domains from originally ≤40 nm² to >200 nm² through an extensive transmission electron microscopy (TEM) study. Additionally, we confirm the integrity of the functional groups during this process by a comprehensive chemical analysis. A closer look into the process confirms the theoretical predicted relevance for the room temperature stability of GO and the development of the composition of functional groups is explained with reaction pathways from theoretical calculations. We further investigate the influence of enlarged graphitic domains on the hydration behaviour of GO and the catalytic performance of single atom catalysts supported by GO. Additionally, we show that the sheet resistance of GO is reduced by several orders of magnitude during the mild thermal annealing process.     

Efficient tri-wavelength actively Q-switched Yb:GAGG laser

An efficient acousto-optic Q-switched Yb-doped Gd₃Al_xGa_5−xO₁₂ (GAGG) (x = 0.5) laser is demonstrated. Under the absorbed pump power of 7.4 W, the maximum average output power of 1.4 W is obtained at the pulse repletion rate of 1 kHz , with the slope efficiency as high as 32%. The pulse width of 40 ns is achieved with the pulse energy and peak power of 1.4 mJ and 35 kW, respectively. What’ more, the output spectrum shows itself tri-wavelength in either CW or Q-switching mode. To our knowledge, this is the first time for realizing simultaneous tri-wavelength Yb:GAGG laser actively Q-switched operation.     

Material design and development: From classical thermodynamics to CALPHAD and ICME approaches

This paper presents an overview and examples of material design and development using (1) classical thermodynamics; (2) CALPHAD (calculation of phase diagrams) modeling; and (3) Integrated Computational Materials Engineering (ICME) approaches. Although the examples are given in lightweight aluminum and magnesium alloys for structural applications, the fundamental methodology and modeling principles are applicable to all materials and engineering applications. The examples in this paper have demonstrated the effectiveness and limitations of classical thermodynamics in solving specific problems (such as nucleation during solidification and solid-state precipitation in aluminum alloys). Computational thermodynamics and CALPHAD modeling, when combined with critical experimental validation, have been used to guide the selection and design of new magnesium alloys for elevated-temperature applications. The future of material design and development will be based on a holistic ICME approach. However, key challenges exist in many aspects of ICME framework, such as the lack of diffusion/mobility databases for many materials systems, limitation of current microstructural modeling capability and integration tools for simulation codes of different length scales.     

Mechanical properties of graphene films enhanced by homo-telechelic functionalized polymer fillers via π–π stacking interactions

Most researches on graphene/polymer composites are focusing on improving the mechanical and electrical properties of polymers at low graphene content instead of paying attention to constructing graphene’s macroscopic structures. In current study the homo-telechelic functionalized polyethylene glycols (FPEGs) were tailored with π-orbital-rich groups (namely phenyl, pyrene and di-pyrene) via esterification reactions, which enhanced the interaction between polyethylene glycol (PEG) molecules and chemical reduced graphene oxide (RGO) sheets. The π–π stacking interactions between graphene sheets and π-orbital-rich groups endowed the composite films with enhanced tensile strength and tunable electrical conductivity. The formation of graphene network structure mediated by the FPEGs fillers via π–π stacking non-covalent interactions should account for the experimental results. The experimental investigations were also complemented with theoretical calculation using a density functional theory. Atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD), nuclear magnetic resonance (NMR), thermal gravimetric analysis (TGA), UV–vis and fluorescence spectroscopy were used to monitor the step-wise preparation of graphene composite films.     

The effect of baking time,fillet radius,and hardness on the lifecycles of pole fastening screws in an electric motor with hydrogen embrittlement

In order to protect bolts from corrosion, electroplating such as zinc plating is widely used. However, hydrogen can easily penetrate or diffuse into the vacancies and dislocations between the lattices of bolt steel during electroplating. As the diffused hydrogen defects inside the lattice are in gaseous form, small cracks can easily be produced due to high pressure from the hydrogen gas. In this research, in order to determine the root cause of the fracture in pole fastening screws resulting from hydrogen embrittlement in typical electric motors, additional factors that accelerate hydrogen embrittlement fracture were selectively applied, including a small fillet in the head–shank transition and excessive hardness, and parametric study was performed experimentally.     

Grain size influence on the flexibility and luminous intensity of inorganic CaTiO3:Pr3+ crystal nanofibers

Traditional inorganic materials exhibit rigidity owing to the lack of polymer chains in polymer materials or atom slipping in metals. However, nanometerization has been recently proposed for the conversion of inorganic oxide materials into flexible materials. Herein, the flexible inorganic luminescent material, CaTiO₃:0.2%Pr³⁺, was synthesized through electrospinning, and the macroscopic flexibility of pure inorganic CaTiO₃:0.2%Pr³⁺ was achieved. The flexible membrane was characterized via X-ray diffraction, thermogravimetry, scanning electron microscopy (SEM), and photoluminescence analyses. The grain size was analyzed at various calcination temperatures via SEM, and the results suggested that the increase in the calcination temperature resulted in the growth of crystal grains. Studies have reported that the growth of crystal grains is beneficial for improving the luminescence performance; however, to obtain better flexibility, smaller crystal grains are required. This study provides an important reference for the design of flexible inorganic materials.     

Classification and regression models of audio and vibration signals for machine state monitoring in precision machining systems

We present a data-driven method for monitoring machine status in manufacturing processes. Audio and vibration data from precision machining are used for inference in two operating scenarios: (a) variable machine health states (anomaly detection); and (b) settings of machine operation (state estimation). Audio and vibration signals are first processed through Fast Fourier Transform and Principal Component Analysis to extract transformed and informative features. These features are then used in the training of classification and regression models for machine state monitoring. Specifically, three classifiers (K-nearest neighbors, convolutional neural networks and support vector machines) and two regressors (support vector regression and neural network regression) were explored, in terms of their accuracy in machine state prediction. It is shown that the audio and vibration signals are sufficiently rich in information about the machine that 100% state classification accuracy could be accomplished. Data fusion was also explored, showing overall superior accuracy of data-driven regression models.     

太赫兹波计算鬼成像:原理和展望

本文立足于太赫兹波成像领域近年来备受关注的研究热点—太赫兹波计算鬼成像,首先回顾了鬼成像从量子到经典再到计算的历史过程,然后阐述了计算鬼成像的数学原理,随后综述了计算鬼成像在太赫兹波段的发展历程,及其在超衍射分辨成像、石墨烯光电导成像、太赫兹光谱成像等方面的应用,并在最后展望了太赫兹波计算鬼成像的发展前景:计算鬼成像作为一种成像手段,可以绕开在太赫兹频段缺乏经济高效的焦面阵列式探测器的难题,但目前的成像帧率还难以满足快速成像的应用需求,相信在未来随着器件性能的提升和成像算法的优化,其成像帧率可以得到大幅提升。     

Can child-pedestrians’ hazard perception skills be enhanced?

ObjectiveTraffic collisions yield a substantial rate of morbidity and injury among child-pedestrians. We explored the formation of an innovative hazard perception training intervention – Child-pedestrians Anticipate and Act Hazard Perception Training (CA²HPT). Training was based upon enhancing participants’ ability to anticipate potential hazards by exposing them to an array of traffic scenes viewed from different angles.MethodTwenty-four 7–9-year-olds have participated. Trainees underwent a 40-min intervention of observing typical residential traffic scenarios in a simulated dome projection environment while engaging in a hazard detection task. Trainees were encouraged to note differences between the scenarios presented to them from separate angles (a pedestrian's point-of-view and a higher perspective angle). Next, trainees and control group members were required to perform crossing decision tasks.ResultsTrainees were found to be more aware of potential hazards related to restricted field of view relative to control.ConclusionsChild pedestrians are responsive to training and actively detecting materialized hazards may enrich child-pedestrians’ ability to cross roads.     

Image Encryption Application of Chaotic Sequences Incorporating Quantum Keys

Machine Intelligence Research - This paper proposes an image encryption algorithm LQBPNN (logistic quantum and back propagation neural network) based on chaotic sequences incorporating quantum...