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Resonance of multi-degree-of-freedom system or structure is a basic and important concept in structural vibration theory, but it lacks a complete and rigorous definition. In order to establish an accurate concept of structural resonance, based on the concept of single-degree-of-freedom system resonance and modal orthogonality, this paper discusses the necessary conditions of system resonance by analyzing the displacement response of multi-degree-of-freedom vibration system, that is, while ensuring that the vibration frequency of the system (a certain natural frequency) is equal to the excitation frequency, its displacement response should also present the corresponding modal shape. An example of simply supported beam is used to illustrate its rationality. At the same time, the theoretical method of pure modal resonance of multi-degree-of-freedom system is given by rational allocation of excitation force. The pure modal resonance of multi-degree-of-freedom system or structure can be realized, which can be used to accurately identify the modal parameters of the structure. It is of great theoretical significance and engineering application value to discriminate the concept of multi-degree-of-freedom system or structure resonance.

An Fe2P nanoparticle (Fe2P NP)-decorated carbon nanofiber (represented as Fe2P@CNF) composite was in situ prepared by electrospinning and subsequent high-temperature treatment. Benefitting from the synergy effect between Fe2P NPs and CNFs, as well as improved interface polarization and impedance matching, the Fe2P@CNF composite exhibits excellent microwave absorption performance relative to pure CNFs, in which the Fe2P@CNF composite with a fill loading of only 10 wt% possesses a minimum reflection loss (RL) of −49.2 dB at 3.0 mm and a maximum effective absorption bandwidth of 6.0 GHz at 2.2 mm. Therefore, this work provides a promising approach for the design and synthesis of an Fe2P@CNF composite with high-performance microwave absorption. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) N-doped carbon nanofibers decorated with ultrafine (∼4.5 nm) SnFe2O4 nanoparticles (denoted as SFO/N-CNFs) are successfully synthesized by a combination of electrospinning and solvothermal process, and their microwave absorption (MA) properties are reported for the first time. With only 5 wt% filler loading in a silicone rubber matrix, the optimum reflection loss (RL) could reach −46.5 dB and the qualified frequency bandwidth (RL < −10 dB) can be capable of 4.8 GHz at 1.6 mm, exhibiting better comprehensive absorption performance relative to other analogous absorbers. The lightweight and highly efficient MA of SFO/N-CNFs is largely ascribed to the improved impedance matching and satisfactory attenuation ability caused by the synergistic effect between the ultrasmall-sized SFO nanoparticles (NPs) and 1D N-CNF matrix. This work not only offers a novel and promising high-performance microwave absorber, but also offers a general approach to designing and fabricating ultrasmall transition metal oxide nanoparticle decorated carbon-based composite nanostructures for multifunctional applications. [ABSTRACT FROM AUTHOR]

The binary composite, ZnSnO3 microcubes (ZSO MC) homogeneously parceled in an N-doped carbon nanofiber membrane (ZSO@CNFM), was synthesized via a mild hydrothermal, electrospinning and carbonization process as a flexible lithium-ion battery (LIB) anode material. The unique carbon-coating layer architecture of ZSO@CNFM not only plays a crucial role in alleviating the volume change of ZSO MC during lithium ion insertion/extraction processes, but also constructs a three-dimensional (3D) transport network with the help of interconnected carbon nanofibers (CNFs) to ensure the structural integrity of the material and promote the electrochemical reaction kinetics. Due to its good flexibility characteristics, the as-prepared ZSO@CNFM can be directly adopted as an anode material for LIBs without the use of copper foil, conductive carbon black and any binder. Electrochemical surveying results manifest that the optimal ZSO@CNFM electrode displays excellent cycling stability (582.6 mA h g−1 after 100 lithiation/delithiation cycles at 100 mA g−1), high coulombic efficiency (CE, 99.6% at 100th cycles), and superior rate performance (349.5 mA h g−1 at 2 A g−1). The good electrochemical properties can be ascribed to the synergistic effect of the high theoretical specific capacity of ZSO MC, favourable stability of the carbon substrate, the open structure of ZSO@CNFM and the 3D continuous highly conductive framework for rapid electron/ion transfer. [ABSTRACT FROM AUTHOR]