Power spectral density analysis for nonlinear systems based on Volterra series

A consequence of nonlinearities is a multi-harmonic response via a monoharmonic excitation.A similar phenomenon also exists in random vibration.The power spectral density(PSD)analysis of random vibration for nonlinear systems is studied in this paper.The analytical formulation of output PSD subject to the zero-mean Gaussian random load is deduced by using the Volterra series expansion and the conception of generalized frequency response function(GFRF).For a class of nonlinear systems,the growing exponential method is used to determine the first 3 rd-order GFRFs.The proposed approach is used to achieve the nonlinear system’s output PSD under a narrow-band stationary random input.The relationship between the peak of PSD and the parameters of the nonlinear system is discussed.By using the proposed method,the nonlinear characteristics of multi-band output via single-band input can be well predicted.The results reveal that changing nonlinear system parameters gives a one-of-a-kind change of the system’s output PSD.This paper provides a method for the research of random vibration prediction and control in real-world nonlinear systems.

Selectivity of biopolymer membranes using HepG2 cells

Bioartificial liver(BAL)system has emerged as an alternative treatment to bridge acute liver failure to either liver transplantation or liver regeneration.One of the main reasons that the efficacy of the current BAL systems was not convincing in clinical trials is attributed to the lack of friendly interface between the membrane and the hepatocytes in liver bioreactor,the core unit of BAL system.Here,we systematically compared the biological responses of hepatosarcoma HepG2 cells seeded on eight,commercially available biocompatible membranes made of acetyl cellulose–nitrocellulose mixed cellulose(CA–NC),acetyl cellulose(CA),nylon(JN),polypropylene(PP),nitrocellulose(NC),polyvinylidene fluoride(PVDF),polycarbonate(PC)and polytetrafluoroethylene(PTFE).Physicochemical analysis and mechanical tests indicated that CA,JN and PP membranes yield high adhesivity and reasonable compressive and/or tensile features with friendly surface topography for cell seeding.Cells prefer to adhere on CA,JN,PP or PTFE membranes with high proliferation rate in spheriod-like shape.Actin,albumin and cytokeratin 18 expressions are favorable for cells on CA or PP membrane,whereas protein filtration is consistent among all the eight membranes.These results further the understandings of cell growth,morphology and spreading,as well as protein filtration on distinct membranes in designing a liver bioreactor.

A comparative analysis of reticular crack on ceramic plate driven by thermal shock

Reticular crack is generally found on the surface of ceramic material that has been subjected to a thermal-shock condition. In the present study, a quantitative effect of thermal shock and quench temperature has been studied and investigated. Experimental tests were carried out to characterize the reticular crack that has been found in the Ge Kiln, which is a famous art of the ancient Chinese culture. After comparative analysis between thermal-shock cracks and the glaze crack patterns of the Ge Kiln porcelain,it is found that this study is expected to provide a powerful tool for recurrence of the long-lost firing and cooling process of the Ge Kiln porcelain.

Multi-parameter joint optimization for double-strip high-speed pantographs to improve pantograph-catenary interaction quality

The significant increase in speed of high-speed train will cause the dynamic contact force of the pantograph-catenary system to fluctuate more severely,which poses a challenge to the study of the pantograph-catenary relationship and the design of highspeed pantographs.Good pantograph-catenary coupling quality is the essential condition to ensure safe and efficient operation of high-speed train,stable and reliable current collection,and reduction in the wear of contact wires and pantograph contact strips.Among them,the dynamic parameters of high-speed pantographs are crucial to pantograph-catenary coupling quality.With the reduction of the standard deviation of the pantograph-catenary contact force as the optimization goal,multi-parameter joint optimization designs for the high-speed pantograph with two contact strips at multiple running speeds are proposed.Moreover,combining the sensitivity analysis at the optimal solutions,with the parameters and characteristics of in-service DSA380 highspeed pantograph,the optimization proposal of DSA380 was given.