Xi'an Jiaotong University

About: Xi'an Jiaotong University is a education organization based out in Xi'an, China. It is known for research contribution in the topics: Heat transfer & Dielectric. The organization has 85440 authors who have published 99682 publications receiving 1579683 citations. The organization is also known as: '''Xi'an Jiaotong University''' & Xi'an Jiao Tong University.

A theory of flexoelectricity with surface effect for elastic dielectrics

Abstract: The flexoelectric effect is very strong for nanosized dielectrics. Moreover, on the nanoscale, surface effects and the electrostatic force cannot be ignored. In this paper, an electric enthalpy variational principle for nanosized dielectrics is proposed concerning with the flexoelectric effect, the surface effects and the electrostatic force. Here, the surface effects contain the effects of both surface stress and surface polarization. From this variational principle, the governing equations and the generalized electromechanical Young–Laplace equations are derived and can account for the effects of flexoelectricity, surface and the electrostatic force. Moreover, based on this variational principle, both the generalized bulk and surface electrostatic stresses can be obtained and are composed of two parts: the Maxwell stress corresponding to the polarization and strain and the remainder relating to the polarization gradient and the strain gradient. The theory developed in this paper provides the underlying framework for the analyses and computational solutions of electromechanical problems in nanodielectrics.

Seismic envelope inversion and modulation signal model

Abstract: We recognized that the envelope fluctuation and decay of seismic records carries ultra low-frequency (ULF, i.e., the frequency below the lowest frequency in the source spectrum) signals that can be used to estimate the long-wavelength velocity structure. We then developed envelope inversion for the recovery of low-wavenumber components of media (smooth background), so that the initial model dependence of waveform inversion can be reduced. We derived the misfit function and the corresponding gradient operator for envelope inversion. To understand the long-wavelength recovery by the envelope inversion, we developed a nonlinear seismic signal model, the modulation signal model, as the basis for retrieving the ULF data and studied the nonlinear scale separation by the envelope operator. To separate the envelope data from the wavefield data (envelope extraction), a demodulation operator (envelope operator) was applied to the waveform data. Numerical tests using synthetic data for the Marmousi model pro...

A Model-Based Method for Remaining Useful Life Prediction of Machinery

Abstract: Remaining useful life (RUL) prediction allows for predictive maintenance of machinery, thus reducing costly unscheduled maintenance. Therefore, RUL prediction of machinery appears to be a hot issue attracting more and more attention as well as being of great challenge. This paper proposes a model-based method for predicting RUL of machinery. The method includes two modules, i.e., indicator construction and RUL prediction. In the first module, a new health indicator named weighted minimum quantization error is constructed, which fuses mutual information from multiple features and properly correlates to the degradation processes of machinery. In the second module, model parameters are initialized using the maximum-likelihood estimation algorithm and RUL is predicted using a particle filtering-based algorithm. The proposed method is demonstrated using vibration signals from accelerated degradation tests of rolling element bearings. The prediction result identifies the effectiveness of the proposed method in predicting RUL of machinery.

A tetraphenylethylene core-based 3D structure small molecular acceptor enabling efficient non-fullerene organic solar cells.

Abstract: A tetraphenylethylene core-based small molecular acceptor with a unique 3D molecular structure is developed. Bulk-heterojunction blend films with a small feature size (≈20 nm) are obtained, which lead to non-fullerene organic solar cells (OSCs) with 5.5% power conversion efficiency. The work provides a new molecular design approach to efficient non-fullerene OSCs based on 3D-structured small-molecule acceptors.

Winter and Summer PM2.5 Chemical Compositions in Fourteen Chinese Cities

Abstract: PM2.5 in 14 of China's large cities achieves high concentrations in both winter and summer with averages >100 μg m−3 being common occurrences. A grand average of 115 μg m−3 was found for all cities, with a minimum of 27 μg m−3 measured at Qingdao during summer and a maximum of 356 μg m−3 at Xi'an during winter. Both primary and secondary PM2.5 are important contributors at all of the cities and during both winter and summer. While ammonium sulfate is a large contributor during both seasons, ammonium nitrate contributions are much larger during winter. Lead levels are still high in several cities, reaching an average of 1.68 μg m−3 in Xi'an. High correlations of lead with arsenic and sulfate concentrations indicate that much of it derives from coal combustion, rather than leaded fuels, which were phased out by calendar year 2000. Although limited fugitive dust markers were available, scaling of iron by its ratios in source profiles shows ∼20% of PM2.5 deriving from fugitive dust in most of the cities. Mult...