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Pure hexagonal β -NaYF4 micron crystals were synthesized by the hydrothermal method with the up-conversion luminescence properties studied by doping Yb 3 + /Ho 3 + . The up-conversion fluorescence spectra and fluorescence lifetime of β -NaYF4 micron crystals were determined by FLS-980 transient fluorescence spectrometer. By changing the doping concentration of Yb 3 + /Ho 3 + , the optimal doping concentration was confirmed to be 20%Yb 3 + /2%Ho 3 + . The fluorescence spectrum was obtained by changing pump power, the relationship between power and intensity was analyzed, and the β -NaYF4 micron crystal green and red emission up-conversion process was obtained into a two-photon process. The 5F 4 → 5 I8 and 5S 2 → 5 I8 of the sample were thermally coupled to obtain a large absolute sensitivity (Sa) of low temperature. The maximum absolute sensitivity within the range of 64–194 K is 0.0097 K − 1 at 144 K, while maximum absolute sensitivity at 333 K is 0.00335 K − 1 in the range of 293–493 K. The experimental results show that the sensing characteristics of β -NaYF4:Yb 3 + /Ho 3 + at low temperature are better than those at high temperature, and it has the potential to be used in the field of temperature sensing. [ABSTRACT FROM AUTHOR]

The isolation technologies are adopted to protect the long-span space structures from serious damage under the action of earthquakes. When the isolation system is applied to the space structures, both horizontal and vertical vibration control effects on the structures should be concerned. In this paper, a two-dimensional earthquake isolation and mitigation device (TEIMD) composed of a high-damping viscoelastic (VE) core pad and VE dampers is proposed. Based on the dynamic shear experiment results of the VE damper, the energy dissipation capability of VE material is preferable. Then, the nonlinear equivalent stiffness and equivalent damping ratio of the TEIMD in horizontal and vertical directions are evaluated by using the numerical simulation method. The TEIMDs are arranged on the column top of a double-layer grid structure to assess the isolation effectiveness of the novel device. The dynamic analysis results of the double-layer grid structure with and without TEIMD reveal that this novel device can significantly reduce the acceleration response of the upper grid by relying on the strong energy dissipation performances in the horizontal and vertical directions. This research also verifies the feasibility of applying the TEIMD to the double-layer grid structure, which can effectively dissipate the vertical vibration energy of the structure. [ABSTRACT FROM AUTHOR]

A conventional plate-type viscoelastic damper (VED) can easily crack at the interfaces of steel plates and viscoelastic components. In the present work, grooved VEDs, which are a new type of interfacial enhanced VEDs with interfacial grooves, are designed to improve the damping capacity and anti-cracking ability of conventional dampers. The dynamic property experiments of the normal and grooved VEDs are carried out and the interfacial cracking failure of the VEDs are simulated and analyzed by using bilayer cohesive constitutive model with ABAQUS. The grooved VED exhibits excellent dynamic performance and energy dissipation capacity at different temperatures, frequencies, and displacement amplitudes. Experiments and finite element analysis prove that the energy dissipation performance and interfacial bonding strength of the grooved VED are effectively improved. A modified fractional standard linear solid model, in which the Payne effect and temperature–frequency equivalent principle are combined and implemented, is proposed. This model can portray the influence of the excitation displacement, surrounding temperature and external excitation frequency on damper properties at the same time. The fillers and molecular chains affections at micro- and meso-scale are also taken into account. The model’s numerical calculations and experimental results comparisons present that the modified fractional standard linear solid model has sufficient accuracy and performs well in depicting the dynamic properties of the interfacial grooved VED. The errors between the theoretical and experimental values of G1 and G2 for the grooved VED are mostly within 20% at representative conditions. The interfacial groove structures can well enhance the interfacial bonding and improve the service life of conventional dampers. The modified fractional standard linear solid model is simple and has clear physical meanings for each macro/micro parameters, making it convenient for application in engineering practice. The present research is of great significance in improving the work stability of VEDs and promoting the application of viscoelastic damping technology. [ABSTRACT FROM AUTHOR]