The Front Cover illustrates the process of closing the gap between the gas phase and the condensed phase. Aggregation effects, the influence of solvent molecules (and counter ions), and differences ...in energy dissipation cause different product distributions in the two environments. The present work describes efforts towards an understanding of the underlying principles, and the concept of pseudo‐gas‐phase conditions constitutes a valuable framework also for the transfer of reactivity. More information can be found in the Research Article by B. Butschke and co‐workers.
The use of existing large pumping station equipment for upstream residual water reverse power generation is an unrealized yet valuable renewable energy project. At present, some large axial flow pump ...stations have begun to perform reverse power generation operations; however, related research has not yet started. In this paper, entropy generation theory is applied to a large-scale axial flow pump station system in reverse power generation operations, and the entropy generation method is used to investigate the accurate size and distribution of the mechanical energy dissipation of each component under different flow conditions. First, the energy characteristics and pressure fluctuations in the pump of the large axial flow pump station system are experimentally tested under reverse power generation conditions. The reliability of the entropy generation numerical calculation is verified both experimentally and theoretically. Then, the proportion of each component in the total entropy production is compared to illustrate how each component contributes to the total entropy production of the system and how this contribution changes as operating conditions vary. Then, the type of entropy production of each component is accurately determined under different flow conditions, revealing the changes in the proportions of the different types of entropy production of each component. Finally, components with large mechanical energy dissipations are selected, and the changes and causes of the energy dissipation distribution of the components are thoroughly analysed under different flow conditions. The research results can aid in better understanding the energy dissipation mechanism of large axial flow pump systems in reverse power generation operations.
This paper reported an experimental and numerical study of a novel brace-type hybrid damper composed of steel slit plates enhanced by the friction mechanism. A test programme including six ...proof-of-concept specimens was carried out. The test results showed that the specimens exhibited multiple yielding stages, and the hysteretic response curves of the specimens were dependent on geometric configurations of the steel slit plates and the clamping force of bolts. The expected energy dissipation sequence accompanied by excellent ductility of the novel hybrid damper specimens was confirmed. The ploughing effect phenomenon between the friction interfaces as evidenced by the wear of the steel plates and increasing friction force was confirmed, which contributed to enhanced friction energy dissipation of the dampers under cyclic loadings. Then, a numerical investigation was conducted to take insights into the resisting mechanism of the specimens. The adequacy of the finite element modelling techniques was justified by a good correlation between test responses and numerical simulations. The test and numerical studies demonstrated that the energy dissipation sequence as a result of the hybrid energy dissipation mechanism contributed to improving the energy dissipation capacity and ductility of the steel slit plates. To facilitate the practical design of the novel hybrid dampers, a theoretical prediction model enabling quantification of critical mechanical quantities of the novel hybrid damper was developed, and the sufficiency of the design model was justified by comparison among the test responses, numerical results, and design predictions.
•A novel brace-type hybrid damper composed of steel slit plates enhanced by the friction mechanism was proposed.•Six damper specimens were designed and physically tested.•Proposed hybrid damper can achieve excellent energy-dissipation capacity and ductility.•The resisting mechanism of the hybrid damper was comprehensively numerical studied.•A theoretical prediction model of the novel hybrid damper was developed.
Alleviating large stress is critical for high‐energy batteries with large volume change upon cycling, yet this still presents a challenge. Here, a gradient hydrogen‐bonding binder is reported for ...high‐capacity silicon‐based anodes that are highly desirable for the next‐generation lithium‐ion batteries. The well‐defined gradient hydrogen bonds, with a successive bond energy of −2.88– −10.04 kcal mol−1, can effectively release the large stress of silicon via the sequential bonding cleavage. This can avoid recurrently abrupt structure fracture of traditional binder due to lack of gradient energy dissipation. Certainly, this regulated binder endows stable high‐areal‐capacity silicon‐based electrodes >4 mAh cm−2. Beyond proof of concept, this work demonstrates a 2 Ah silicon‐based pouch cell with an impressive capacity retention of 80.2% after 700 cycles (0.028% decay/cycle) based on this gradient hydrogen‐bonding binder, making it more promising for practical application.
A gradient H‐bonding polymer binder for Si‐based anodes is reported, where the H‐bond energies are regulated in a wide range. The well‐defined gradient hydrogen bonds can effectively release stress and maintain the integrity of the electrode via sequential bonding cleavage. Additionally, a 2 Ah pouch cell with an impressive capacity retention makes this binder more promising for practical application.
•State-of-the-art review on friction type passive energy dissipation devices.•Development and application of passive dry friction damper is presented chronologically.•Limitations, challenges, and ...uncertainties associated with friction dampers are discussed.•Future research directions are highlighted.
This paper presents a state-of-the-art review on friction type passive energy dissipation devices. Friction dampers are highly preferred as an energy dissipation device, particularly for the seismic fortification of the engineering structures due to their simplicity, reliability, and maximum energy dissipation as a result of the generation of rectangular hysteretic loops. Additionally, their performance is not significantly influenced by the loading amplitude, frequency, and the number of cycles. Hence, with a better understanding of friction mechanism and behavior, numerous novel passive dry friction dampers have been invented and applied in the field of civil engineering since 1980. However, decades of studies over these dampers are highly scattered throughout the academic community. Hence, the availability of many valuable pieces of research is out of reach for further studies. Therefore, a holistic chronological detail of advancement (development and application) in the field of passive friction dampers has been presented systematically in this study. The major purpose of this paper is to present an integrated and holistic overview of passive friction damper for the ease of further studies and generate future research directions for researchers who will be working in this field.
Material dissipation of graphene resonators Ben-Shimon, Yahav; Pradhan, Anway; Ya'akobovitz, Assaf
Carbon (New York),
September 2023, 2023-09-00, Letnik:
213
Journal Article
Recenzirano
Graphene resonators hold a promising potential to be integrated into nanoscale sensors and electronic devices. Therefore, understanding the physics underlying their dissipation mechanisms is ...essential. Here we investigate the dissipation of graphene through a study of graphene foam (GF) resonators. We show that intrinsic material dissipation, related to interlayer friction, is a primary source of energy dissipation in graphene. We fabricated GFs with varying wall thicknesses and characterized their frequency responses under ambient and vacuum conditions. Additionally, we investigated their atomic structure by using Raman analysis, high-resolution scanning electron microscopy, and transmission electron microscopy. While air losses are considered the primary dissipation source of micro- and nano-electromechanical systems (M/NEMS) operating under ambient conditions, we show that friction between graphene layers is a comparable source for energy dissipation and, thus, it limits the dynamic amplification of multilayer graphene resonators even when they are operated under high-vacuum conditions. We show that the friction between the layers is enhanced when multiple layers exist and that dissipation is further amplified by microscopic defects, such as cracks and grain boundaries, or by the existence of amorphous carbon. Thus, we uncover the fundamental physical behavior of graphene.
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•We study energy dissipation in graphene resonators.•We excited resonators under ambient and vacuum conditions, SEM and TEM analyses.•Layer friction was found to be the main source for energy dissipation.•Grain boundaries, micro-cracks, and amorphous carbon enhance the dissipation.
Fluid viscous dampers (FVDs) are well-established supplemental energy dissipation devices that have been widely used for earthquake protection of structures. Optimal design, placement and sizing of ...FVDs have been extensively investigated in the last four decades. In this review paper, an overview of the most popular methodologies from the abundant literature in the field is presented. Key aspects and main characteristics of the different strategies to identify the optimal damping coefficients and the optimal placement of FVDs are scrutinized in a comparative manner. The optimal design problem is often solved through a numerical approach to a constrained optimization problem, by minimizing some performance criteria that are representative measures of the system response. With reference to two simple benchmark six-story shear-type structures subject to both a stochastic earthquake excitation and 44 natural ground motions extracted from the FEMA P695 record set, comparison of the seismic performance is carried out considering FVDs designed according to different methods — an overall number of 138 different design scenarios are incorporated in this comparative study. These methods are based either on a desired (target) damping ratio constraint or on a fixed total cost, here roughly related to the sum of the damping coefficients of the added FVDs. Some energy-based perspectives are also given in this review paper in order to interpret the seismic performance in terms of the amount of energy dissipated by the FVDs, out of the total input energy from the earthquake excitation.
•A review of methodologies for the optimal design of FVDs is presented.•Key aspect and main characteristics of different strategies are outlined.•New energy-based perspectives for the optimal design of FVDs are proposed.•Extensive comparative study among different methodologies proposed in the literature.
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