Influence of the Autoregressive Model Order on Damage Detection

Abstract: An important step for using time‐series autoregressive (AR) models for structural health monitoring is the estimation of the appropriate model order. To obtain an optimal AR model order for such processes, this article presents and discusses four techniques based on Akaike information criterion, partial autocorrelation function, root mean squared error, and singular value decomposition. A unique contribution of this work is to provide a comparative study with three different AR models that is carried out to understand the influence of the model order on the damage detection process in the presence of simulated operational and environmental variability. A three‐story base‐excited frame structure was used as a test bed in a laboratory setting, and data sets were measured for several structural state conditions. Damage was introduced by a bumper mechanism that induces a repetitive impact‐type nonlinearity. The operational and environmental effects were simulated by adding mass and by changing the stiffness properties of the columns. It was found that these four techniques do not converge to a unique solution, rather all require somewhat qualitative interpretation to define the optimal model order. The comparative study carried out on these data sets shows that the AR model order range defined by the four techniques provides robust damage detection in the presence of simulated operational and environmental variability.     

Influence of nickel ions on human multipotent mesenchymal stromal cells (hMSCs)

Nickel‐Titanium‐Shape‐Memory‐Alloys (NiTi‐SMA) are of biomedical interest due to an unusual range of pure elastic deformability (superelasticity) and the shape memory effect which allows this material to return to a predictable previously memorized shape after external changes in temperature. HMSCs (human multipotent mesenchymal stromal cells) are currently the most promising cell type for regenerative medicine and tissue engineering, due to the ability to differentiate into several tissues such as bone, tendon, cartilage or muscle. For tissue engineering newly developed porous NiTi‐SMA materials are evaluated preloaded with hMSCs. For biocompatibility testing the high nickel content (50 %at) of NiTi‐SMA plays a critical role. To analyse the influence of Ni‐ions on hMSCs viability and activation, cells were cultured with or without NiCl₂ for 24h and 7days. Cells were either seeded in media containing NiCl₂ or the NiCl₂ was later added to already adherent cells. Cell metabolism, proliferation and viability were analysed by alamarBlue^TM assay or fluorescence microscopy. Cytokine (IL‐6, 8, 11) release from hMSCs was determined by ELISA . NiCl₂ concentrations below 25 μg/ ml were well tolerated by the cells. A significant decrease in cell proliferation occurred at threshold values of 200 μg/ ml (24 h) and 25 μg/ ml (7 d). There was a significant, dose dependent increase in the release of IL‐8 from hMSCs cultured in the presence of sub toxic NiCl₂ concentrations. The present study demonstrates for the first time that high but non‐toxic concentrations of Ni²⁺ are capable to activate hMSCs. Thus high Ni²⁺ concentrations apart from allergen‐ or particle‐induced inflammation, may lead to tissue inflammation in the vicinity of a NiTi‐SMA implant in vivo and subsequently to implant failure e.g. due to implant loosening.     

金属玻璃蠕变及回复行为研究综述

由于非晶合金独特的无序结构,其结构动力学特征涉及较大时间与尺寸跨度的粒子重排。作为深入研究金属玻璃体系弛豫行为与老化动力学的基础,对非晶合金结构动力学的表征和理解至关重要。大量研究表明,以镧基和铈基为代表的稀土基非晶合金的弛豫谱呈现明显次级弛豫过程,该体系亦成为探究非晶合金结构动力学与力学性能关联的理想载体。本文主要就金属玻璃的滞弹性变形作了详细评述。作为蠕变实验中变形的主要成分,这类变形在卸载后可完全回复,对其合理描述是深入理解非晶合金结构动力学的关键。此外,总结了蠕变和蠕变回复过程中滞弹性变形的主要特征,并介绍了几种可用于定量或定性分析的理论模型。     

Experimental and clinical experience with new pyeloureteral stents in pediatric urology

In light of the many problems with the use of conventional external stents in supravesical reconstructive urinary tract surgery in children; e.g. the risk of infection, urodynamic malfunction, and lack of flexibility insertion methods, the return to internal pyeloureteral stenting is a much discussed topic in pediatric urology. In order to improve the generally unsatisfactory situation, we developed, together with the Rüsch Co., a new type of directable and deconnectable ureteral stent. This polyurethane catheter features a membrane valve made of soft Wiruthan at the bladder end, which closes automatically with increasing bladder pressure. Thus, urinary backflow from the urinary bladder into the renal pelvis is prevented. Experimental data from antireflux stenting justify the clinical use of such a stent in children, as the urodynamic in vivo criteria and requirements were fulfilled completely. We now have clinical experience with the application of 340 pyeloureteral DD stents in 241 children from 1993 through 1996; 259 stents were inserted intraoperatively, and 81 stents were applied by endoscope. It was impressive that secondarily, renal function that had been considerably reduced could be regained and stabilized by long-term stenting, even in some older children with chronic supravesical ureteral obstruction. Although small technical details have to be clarified, such as simplification of stent retrieval and an antireflux valve that can be applied using an anterograde approach, the DD valve stent used in this patient population after reconstruction of a malformed supravesical urinary tract can be recommended without any reservations.     

Diffusion in gels

The diffusion of solutes in gels is comprehensively reviewed. Because it has been a source of confusion, precise definitions of the gel diffusion coefficient are presented and discussed. Theories as to the effect of the gel substance on the course of diffusion are critically evaluated. These include the obstruction effect, hydrodynamic drag and other frictional couplings, alteration of solvent properties and (for homogeneous gels) the free volume theory. A large proportion of the data on diffusion in gels to be found in the literature is displayed, with the exception of those systems where binding of the solute is a major factor. The success of the theories in accounting for these results is examined. It is concluded that for heterogeneous gels the obstruction effect is prevalent, for organic solvent-polymer systems the free volume theory has had some success while diffusion of both macromolecules and micromolecular solutes in homogeneous gels is not well understood and deserves more experimental effort.     

Anwendung des Paschen-Gesetzes für die Optimierung des Wickelkopf-Abstandsdesigns von gro?en rotierenden elektrischen Maschinen

Today there is a great demand for optimization of the overall performance of high voltage rotating machines. In the endwinding minimized distances between adjacent insulated bars or coils and reduced insulation thickness at constant voltage stress increase the requirements on the insulating system. Therefore the endwinding design has to be optimized with regarding to corona discharges and axial size reduction. This paper describes our research about physics of gas discharges under various environmental conditions. In particular we investigated plane-plane arrangements of insulated electrodes with and without spacers. Thereby, special attention is paid to corona inception and extinction voltage as well as the occurred level of partial discharges (on the basis of phase resolved PD patterns). Comparing the obtained results with the classical Paschen’s Law will allow an optimized endwinding design in future.     

现代架空线输电系统中的高压电缆段

Electrical power transmission is dominated by overhead line systems at present.This is mainly based on more than hundred years of experience of utilities in running overhead lines.Furthermore,overhead lines have proven their operational reliability and functional assurance.In the past,cables were used in distribution networks in urban areas for the most part with the exception of direct current submarine cables.New developments of high voltage XLPE cables make it possible to use this technology for EHV level applications in transmission networks.Within this paper,mixed network configurations,consisting of overhead lines and high voltage cables,are investigated.An exemplary EHV transmission line with a total length of about 100 km,which is quite typical for Central Europe,has been studied.Several different line combinations are discussed with varied rates between overhead line sections and cable sections length in practice.The length of the cable sections are ranging from several kilometers up to lengths of 100 km.In this paper the work focuses on the transient behavior of combined 400 kV overhead and cable lines during switching processes and lightning impacts.A number of calculations were carried out to get an overview of the transient stress in numerous network nodes along the transmission system.Numerical programs like ATP/EMTP have been used for these simulations.Peak values and wave shapes of the transient voltage stress have been evaluated,based on different systems and within possible combinations.In respect of the insulation coordination and transient stress at network nodes,the voltage-time trends are also analyzed.The combination of high voltage overhead and cable transmission systems,especially such with lengths of more than about 50 km,are making tightened and extended demands to the network design,to the operational management and of course to the network protection also.As an output of this investigations,the results might influence the strategy in running this new type of combined transmission systems.