Surface functionalization of vertical graphene significantly enhances the energy storage capability for symmetric supercapacitors

Vertical graphene (VG) sheets, which consist of few-layer graphene vertically aligned on the substrate with three dimensionally interconnected porous network, make them become one of the most promising energy storage electrodes, especially for SCs. Nevertheless, the intrinsic hydrophobic nature of pristine VG sheets severely limited its application in aqueous SCs. Here, electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to improve charge storage performance. Our work demonstrated that the introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudo capacitance to increase the specific capacitance. The resulting capacitance of electrochemically oxidized VG for 7 min (denoted as EOVG-7) exhibited three orders of magnitude higher (1605 mF/cm²) compared to pristine VG sheets. Through assembled two EOVG-7 electrodes, a symmetric supercapacitor demonstrated high specific capacitance of 307.5 mF/cm², high energy density of 138.3 μWh/cm2 as well as excellent cyclic stability (84% capacitance retention after 10000 cycles). This strategy provides a promising way for designing and engineering carbon-based aqueous supercapacitors with high performance

Yangtze floods recorded on Mt. Mufu and Swallow Cliff in Nanjing, China

The Yangtze drainage basin is the most densely populated and prosperous area of China; however, it is frequently threatened by floods. The Holocene flood lines of the Yangtze River have been preserved on Mt. Mufu and Swallow Cliff in north-eastern Nanjing, and they are characterised by the presence of particular colour tones and the horizontal arrangement of erosional pits and holes. Four major paleo-flood lines at altitudes of 8.51, 9.43, 10.47, and 12.84 m were identified via a field survey along the river bank. Historical literature and instrumental flood records extend the paleo-flood stage to the contemporary era and indicate that the highest flood line of 12.84 m represents a maximum limit for future floods. Besides, the flood line at 10.47 m can be regarded as a foreseeable extreme flood risk level with a recurrence interval of 100–200 years, especially considering the current circumstances of rising sea levels and decreasing flood storage capacities caused by human activities

Ground Displacement Variation Around Power Line Corridors on the Loess Plateau Estimated by Persistent Scatterer Interferometry

As the world’s largest producer and consumer of electricity, China has deployed a project to transport energy resources from West China to East China through extra-high-voltage transmission lines to reduce carbon emissions. In the Loess Plateau, the safety of transmission lines has been frequently threatened by natural hazards such as landslides and ground subsidence. However, it is prohibitively expensive to build a monitoring network covering all transmission lines to provide timely early warnings, particularly for sparsely inhabited areas. Based on the large-scale coverage of Sentinel-1 SLC images in IW TOPS mode, we utilized persistent scatterer interferometry to measure the ground target movements along transmission lines with millimeter accuracy. Three regions of interest were selected to reflect the different environmental conditions from the south to north of the Yan’an Region. The displacement variations were compared and evaluated at three spatial scales (region, route, local) from October 2018 to November 2019. On the regional scale, the deformation variation decreased from the south (−36 – 29 mm/yr) to the north (−19 – 20 mm/yr), which was significantly different as determined by the analysis of variance (ANOVA) and can be attributed to the impacts of water-induced subsidence and human activities. On the local scale, the results showed that the deformation rate was less than 10 mm/yr, which suggested a stable status for the experimental line sections. The displacement time series of transmission towers preliminarily revealed seasonal displacement variations, wherein winter and spring were relatively quiet periods. The application of advanced InSAR technologies has excellent prospects in smart grid implementation

Contribution à l'étude de l'impact des nanotechnologies sur les architectures (apprentissage d'inspiration neuronale de fonctions logiques pour circuits programmables)

Au regard de l intérêt porté envers les nanotechnologies, l objectif de ce travail de thèse est d étudier l architecture bioinspirée des nanocomposants pour la réalisation d un bloc de mémoire associative en guise du bloc de calcul logique universel. La première partie du manuscrit s intéresse aux problématiques des méthodes de fabrication contemporaine, puis l étude des propriétés des nanocomposants comme l alternative éventuelle. En seconde partie le développement de l'architecture des réseaux de neurones est décrit en détails dans le contexte des circuits reconfigurable. Pour la dernière partie, la robustesse est évaluée par simulation fonctionnelle. Il est alors question d étudier la redondance des réseaux, qui est inhérente à ce type d architecture. Les simulations montrent la possibilité de construire ce genre de circuit robuste grâce à l apprentissage neuronal.The objective is to study bioinspired architecture of nanocomposants for associative memory unit as a universal logic and arithmetic processing element. The first part of the manuscript deal with the analysis of issues of deployed process and study of nanocomponents. In the second part, the development of neural network based architecture is described in the context of reconfigurable circuits. For the last part, the defect tolerance of the architecture is assessed by functional simulations in redundant networks. The simulations showed the entire feasibility of such circuit through neural learning process.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Assessment on the energy flow and carbon emissions of integrated steelmaking plants

China’s iron and steel industry has developed rapidly over the past two decades. The annual crude steel production is nearly half of the global production, and approximately 90% of the steel is produced via BF–BOF route that is energy-intensive. Based on the practice of integrated steelmaking plants, a material flow analysis model that includes three layers, i.e., material, ferrum, and energy, was constructed on process levels to analyze the energy consumption and carbon emissions according to the principle of mass conservation and the First Law of Thermodynamics. The result shows that the primary energy intensity and carbon emissions are 20.3 GJ/t and 0.46 tC/t crude steel, respectively, including coke and ancillary material’s preparation. These values are above the world’s average level of the BF–BOF route and could be regarded as a high-performance benchmark of steelmaking efficiency. However, the total energy consumption and carbon emission from steelmaking industry were approximately 13095 PJ and 300 MtC, respectively, on the best practice estimation in 2011, and are still large numbers for achieving the goal of reducing global warming. The potential carbon reduction will be limited if no significant changes are undertaken in the steel industry

On a Symmetric Image Encryption Algorithm Based on the Peculiarity of Plaintext DNA Coding

Many plaintext-related or non-plaintext-related image encryption algorithms based on chaotic systems have been found inefficient and insecure under chosen plaintext attacks. In this paper, a novel plaintext-related mechanism based on the peculiarity of plaintext DNA coding (PPDC) is presented and used to developed a symmetric image encryption algorithm. In our scheme, a hyper-chaotic Lorenz system is used to produce four chaotic sequences. Firstly, by using one chaotic sequence to control the DNA rules, the original image is encoded to obtain the image DNA coding and PPDC, and another chaotic sequence is encoded into a DNA sequence, which is used in the DNA XOR operation. Then, the processing of the remaining two chaotic sequences by using the PPDC is performed to obtain two key streams, which are used in the permutation stage. After performing the traditional permutation operation and DNA XOR operation, the cipher image is obtained. Because of the use of the PPDC, the key streams used in the permutation stage are related to the secret keys and plaintext image, which gives the encryption system higher plaintext sensitivity and security. The simulation experimental results and security analysis demonstrate that the proposed encryption system possesses high efficiency and security and can resist various typical attacks like exhaustive attack, statistical attack, and differential attack effectively

Dynamic Characteristics of Unsteady Aerodynamic Pressure on an Enclosed Housing for Sound Emission Alleviation Caused by a Passing High-Speed Train

Train speed is increasing due to the development of high-speed railway technology. However, high-speed trains generate more noise and discomfort for residents, enclosed housing for sound emission alleviation is needed to further reduce noise. Because these enclosed housings for sound emission alleviation restrain the air flow, strong and complicated aerodynamic pressures are generated inside the housing for sound emission alleviation when a train passes through at a high speed. This train-induced aerodynamic pressure, particularly its dynamic characteristics, is a key parameter in structural design. In the present study, the train-induced unsteady aerodynamic pressure in an enclosed housing for sound emission alleviation is simulated using the dynamic mesh method, and the dynamic characteristics of the aerodynamic pressure are investigated. The simulation results show that when the train is running in the enclosed housing for sound emission alleviation, the unsteady aerodynamic pressure is complicated and aperiodic, and after the train leaves the housing for sound emission alleviation, the aerodynamic pressure reverts to periodic decay curves. Two new terms, the duration of the extreme aerodynamic pressure and the pressure change rate, are proposed to evaluate the dynamic characteristics when the train passes through the barrier. The dominant frequency and decay rate are adopted to express the dynamic characteristics after the train exits. When the train runs in the enclosed housing for sound emission alleviation, the longest durations of the positive and negative extreme aerodynamic pressures are in the middle section, and the maximum change rate of aerodynamic pressure occurs at the entrance area. After the train exits the housing for sound emission alleviation, the pressure amplitude at the central region is always higher than those close to the entrance/exit. The dominant frequency of the aerodynamic pressure is identified and explained using wave propagation theory, the decay rate of the aerodynamic pressure at all sections is close