Dongyi Liu  Rumeng Han  Genqi Xu 《International journal of control》2020,93(5):1220-1230

For a distributed parameter system with an input delay in the boundary, a feedback control law is presented by means of the backstepping method. The square integrability of input signal is verified based on the target system. Then, the boundedness and invertibility of the corresponding backstepping transformation are proved under the regularity of system and the admissibility of feedback operator. Thus, the resulting closed-loop system is shown to be exponentially stable. Finally, as an application, a numerical simulation of a one-dimensional Schrödinger equation with a delay input is carried out, and the simulation results demonstrate the effectiveness of the suggested control law.  相似文献   

    

Min Young Doo  Curtis J. Bonk 《Journal of Computer Assisted Learning》2020,36(6):997-1010

Flipped learning recently gained attention as an effective instructional approach to enhance learning engagement, causing many universities to implement it. To enhance student engagement in large university classes, this study examined the effects of self-efficacy, self-regulation and social presence on learning engagement in a large university class using a flipped learning approach. A total of 390 undergraduates who were enrolled in a large general education class using flipped learning at a university in Korea participated in this study. The learners completed an online survey measuring the variables of this study. The research findings indicated that self-regulation affected social presence as well as learning engagement. Self-efficacy affected social presence and indirectly affected learning engagement through social presence. Finally, social presence affected learning engagement. Social presence also mediated the relationship between self-efficacy and learning engagement as well as between self-regulation and learning engagement. This study confirmed the significant effects of self-regulation and social presence on students' learning engagement in large university classes.  相似文献   

    

《International Journal of Hydrogen Energy》2020,45(52):28163-28174

Element replacement and mechanical milling are considered as the most effective ways to improve Mg-based alloys in their hydrogen storage performance. The as-milled La₇RE₃Mg₈₀Ni₁₀ (RE = Sm, Ce) alloys were prepared in this experiment by introducing both element replacement (replacing La by Ce or Sm partially) and mechanical milling technologies. The influence made by different replacing elements on the structure and hydrogen storage property of La₇RE₃Mg₈₀Ni₁₀ (RE = Sm, Ce) alloys was investigated in detail. X-ray diffraction, transmission electron microscope, automatic Sievert apparatus, thermogravimetry and differential scanning calorimetry were used to investigate the experimental alloys. The experiment reveals that a nanocrystalline and amorphous structure appears after mechanical milling. Moreover, comparing with the RE = Sm alloy, the RE = Ce alloy has a superior hydrogen desorption property, including larger hydrogen absorption capacity, faster hydriding/dehydriding rate, lower onset hydrogen desorption temperature, and lower dehydrogenation activation energy.  相似文献   

    

《International Journal of Hydrogen Energy》2020,45(24):13365-13375

A new proton conductor based on 1H-1,2,3-triazole doped nanocrystalline cellulose (2.66 CNC-Tri) has been synthesized for possible use as an electrolyte in proton exchange membrane (PEM) cells. The physicochemical properties of 2.66 CNC-Tri were determined and compared with those of imidazole-doped nanocrystalline (1.17 CNC-Im) and pure nanocrystalline cellulose (CNC). The composites were obtained in the form of a film and their synthesis proceeded under vacuum. The maximum conductivity of 2.66 CNC-Tri was measured to be 0.1 × 10⁻⁴ S/m at 175 °C and that of 1.17 CNC-Im to be 1.6 × 10⁻² S/m at 155 °C, in the anhydrous state. The composite 2.66 CNC-Tri, compared to 1.17 CNC-Im, has much better thermal properties manifested as stability of the matrix and durability of the heterocyclic molecule. The lifetimes of 2.66 CNC-Tri fulfills the requirements of the U.S. Department of Energy for the minimum lifetimes of a PEM based fuel cell for cars.  相似文献   

    

《International Journal of Hydrogen Energy》2020,45(48):25838-25850

The increase of renewable share in the energy generation mix makes necessary to increase the flexibility of the electricity market. Thus, fossil fuel thermal power plants have to adapt their electricity production to compensate these fluctuations. Operation at partial load means a significant loss of efficiency and important reduction of incomes from electricity sales in the fossil power plant. Among the energy storage technologies proposed to overcome these problems, Power to Gas (PtG) allows for the massive storage of surplus electricity in form of hydrogen or synthetic natural gas. In this work, the integration of a Power to Gas system (50 MWe) with fossil fuel thermal power plants (500 MWe) is proposed to reduce the minimum complaint load and avoid shutdowns. This concept allows a continuous operation of power plants during periods with low demand, avoiding the penalty cost of shutdown. The operation of the hybrid system has been modelled to calculate efficiencies, hydrogen and electricity production as a function of the load of the fossil fuel power plant. Results show that the utilisation of PtG diminishes the specific cost of producing electricity between a 20% and 50%, depending on the framework considered (hot, warm and cold start-up). The main contribution is the reduction of the shutdown penalties rather than the incomes from the sale of the hydrogen. At the light of the obtained results, the hybrid system may be implemented to increase the cost-effectiveness of existing fossil fuel power plants while adapting the energy mix to high shares of variable renewable electricity sources.  相似文献   

    

C. BOULOGNE  C. GILLET  L. HUGHES  R. LE BARS  A. CANETTE  C.R. HAWES  B. SATIAT-JEUNEMAITRE 《Journal of microscopy》2020,280(2):86-103

Up-to-date imaging approaches were used to address the spatiotemporal organisation of the endomembrane system in secretory cells of Dionaea muscipula. Different ‘slice and view’ methodologies were performed on resin-embedded samples to finally achieve a 3D reconstruction of the cell architecture, using ultrastructural tomography, array tomography, serial block face-scanning electron microscopy (SBF-SEM), correlation, and volume rendering at the light microscopy level. Observations of cryo-fixed samples by high-pressure freezing revealed changes of the endomembrane system that occur after trap activation and prey digestion. They provide evidence for an original strategy that adapts the secretory machinery to a specific and unique case of stimulated exocytosis in plant cells. A first secretion peak is part of a rapid response to deliver digestive fluids to the cell surface, which delivers the needed stock of digestive materials ‘on site’. The second peak of activity could then be associated with the reconstruction of the Golgi apparatus (GA), endoplasmic reticulum (ER) and vacuolar machinery, in order to prepare for a subsequent round of prey capture. Tubular continuum between ER and Golgi stacks observed on ZIO-impregnated tissues may correspond to an efficient transfer mechanism for lipids and/or proteins, especially for use in rapidly resetting the molecular GA machinery. The occurrence of one vacuolar continuum may permit continuous adjustment of cell homeostasy. The subcellular features of the secretory cells of Dionaea muscipula outline key innovations in the organisation of plant cell compartmentalisation that are used to cope with specific cell needs such as the full use of the GA as a protein factory, and the ability to create protein reservoirs in the periplasmic space. Shape-derived forces of the pleiomorphic vacuole may act as signals to accompany the sorting and entering flows of the cell.  相似文献   

    

Prof. Dr. techn. Andreas Taras  Armin Kager Dipl.-Ing.  Dipl.-Ing. Dr. techn. Dieter Theiner  Dipl.-Ing. Dr. Valentina Cavedon 《Stahlbau》2020,89(5):424-438

Assessment of existing steel penstocks in hydropower plants – strategies in the context of the installations in South Tyrol Steel penstocks carry water over large distances and often steep changes of altitude from the water catchment to the turbines in the powerhouse. As structural elements and – simultaneously – fluid transport lines, they represent steel structural elements that are loaded in a very high and complex manner. For the operators of hydropower plants, the assessment of the structural condition and the associated risks of steel penstocks thus represents one of the crucial steps needed to obtain, renew and maintain an operating concession from public authorities. Assessments of this type were carried out systematically over the course of the last few years for the many hydropower plants in the Italian Autonomous Province of Bolzano – South Tyrol, due to their particular significance for the energy supply of the region and the advanced service life of many plants. The assessment of the structural health and safety of existing, ageing steel penstocks thereby requires expertise drawn from various disciplines and reports from literature, due to the fact that no encompassing, dedicated standard or code of practice for this task is currently available that fully reflects the current state of the art in the reliability and strength of steel structures for this type of components. In fact, steel penstocks in hydropower plants share some features with civil steelwork structures and others with pressure vessels and components. Non-destructive testing techniques as well as advanced, non-linear numerical calculations thus play a significant part. This article gives a summary of the methods and techniques recently applied for the assessment of steel penstocks in South Tyrol.  相似文献   

    

Prof. Dr.-Ing. Daniel Pak  Prof. Dr. Günter Seidl 《Stahlbau》2020,89(3):240-249

A short history of frame bridges in Germany – from steel frame bridges to integral abutment bridges Steel frame bridges have been used in Germany since the beginning of the last century. While the first steel frames were still riveted, at the beginning of the 1940s spans of up to 50 m could already be achieved with welded, full-walled double-jointed frame bridges. Due to their slenderness, they were used, among other things, when increased live loads required a replacement. While the support conditions of the originally erected two hinged frames were still clearly defined, the construction of bridges with integral abutments required the development of new approaches to take account of soil-structure interaction. Today, frame bridges have become an economical alternative due to their large feasible span width, which makes the central pier superfluous for motorway overpasses, and their low life cycle costs. The short history of frame bridges presented here does not claim to be complete, but is intended to illustrate the development over the last 100 years using selected examples.  相似文献   

    

Prof. Dr.-Ing. Karsten Geißler  Gregor Gebert Dipl.-Ing. 《Stahlbau》2020,89(2):148-163

Design, construction and calculation specifications of current large composite bridges At the next few years numerous large bridges in the network of federal highways will have to be replaced. At structural design the composite deck bridges are often preferred because of advantages by prefabrication and quick installation. At the present contribution current developments of these composite bridges are discussed with special regard to structural design including the cross-sectional design as well as construction details. Finally some current DEGES projects are presented  相似文献   

    

Juan Fernando Hidalgo-Cordero  Esteban Revilla  Justo García-Navarro 《Journal of Natural Fibers》2020,17(7):954-965

ABSTRACT

Totora (Schoenoplectus californicus (C.A. Mey.) Soják) is a sedge that grows in lakes and marshes in America and some of the Pacific Islands. The hypothesis tested was that the rind and pith of totora stems have different chemical characteristics. A higher ash content on the pith (7.81% vs. 6.36%) may indicate strategies of the plant to reinforce the aerenchyma tissue and clarify the storage mechanism of compounds by bio mineralization. Almost double acid-insoluble lignin content in the rind (16.42% vs. 8.90%) may indicate the potential optimization of industrial procedures such as paper production by using specific tissues of the plant.  相似文献