Structural damage identification by adding virtual masses

This paper presents a method for damage identification by adding virtual masses to the structure in order to increase its sensitivity to local damages. The main concept is based on the Virtual Distortion Method (VDM), which is a fast structural reanalysis method that employs virtual distortions or pseudo loads to simulate structural modifications. In this paper, the structure with an added virtual mass is called the virtual structure. First, the acceleration frequency response of the virtual structure is constructed numerically by the VDM using local dynamic data measured only by a single excitation sensor and a single acceleration sensor. Second, the value of the additional mass is determined via sensitivity analysis of the constructed frequency responses of the virtual structure with respect to damage parameters; only the natural frequencies with high sensitivity are selected. This process is repeated for all the considered placements of the virtual mass. At last, the selected natural frequencies of all the virtual structures are used together for damage identification of the real structure. A finite element (FE) model of a plane frame is used to introduce and verify the proposed method. The damage can be identified precisely and effectively even under simulated 5 % Gaussian noise pollution.     

Identification of coexistent load and damage

Load reconstruction and damage identification are crucial problems in structural health monitoring. However, it seems there is not much investigation on identification of coexistent load and damage, although in practice they usually exist together. This paper presents a methodology to solve this problem based on the Virtual Distortion Method. A damaged structure is modeled by an equivalent intact structure subjected to the same loads and to virtual distortions which model the damages. The measured structural response is used to identify the loads, the distortions and to recover the stress-strain relationship of the damaged elements. This way both the damage type and extent are identified. The approach can be used off-line and online by repetitive applications in a moving time window. A numerical experiment of a truss with 5% measurement error validates that the two tested damage types (constant stiffness reduction and breathing crack) can be identified along with the loads.     

Assessment of the hydromorphological state of Carpathian rivers above and below reservoirs

The article presents the results of an assessment of the hydromorphological state of selected Carpathian rivers in sections above and below the reservoirs. An attempt has also been made to assess the impact of reservoirs on the hydromorphological conditions and quality of river habitats. The research was based on the River Habitat Survey (RHS) method. The synthetic indices Habitat Quality Assessment (HQA) and Habitat Modification Score (HMS) were calculated on the basis of the gathered data for each section studied; this allowed the hydromorphological qualities of the rivers to be assessed numerically. The reservoirs interrupt river continuum, and they alter different biotic and abiotic elements of natural environment. However, this study has shown that the operation of reservoirs does not always negatively impact the hydromorphological conditions of rivers that reflect their habitat quality. The influence of reservoirs on a river's hydromorphological state above and below a reservoir's location may be neutral, but it also can improve the habitat conditions of a river.     

Probabilistic model for the annual number of storm overflow discharges in a stormwater drainage system

The paper presents an attempt to develop a probabilistic model for predicting an annual number of storm overflow discharges. Forecasting the occurrence of an overflow discharge event involved the application of the logistic regression, which does not require the development of complex hydrodynamic catchment models. The performed calculations showed that the logistic regression model can be successfully used to evaluate the performance of the emergency overflow weir. The resultant logit model eliminates the necessity to develop hydrodynamic models, to conduct continuous measurements of the flow intensity in the stormwater drainage system and to collect detailed information on the characteristics of the subcatchments within the analyzed catchment. The hydrodynamic model was used to simulate the annual number of discharges. The analysis of the results demonstrated that they are in the range of stochastic values, which indicates an application-related character of the method.     

Electrically active defects in SiC Schottky barrier diodes

The electrical properties of deep-level defects in real packaged SiC Schottky barrier rectifiers were studied by deep level transient spectroscopy (DLTS). One deep-level trap with an activation energy in the 0.29–0.30 eV range was revealed to be present in all the tested samples. The electrical characteristics of the trap indicate it is probably attributed to dislocations or to metastable defects, which can be responsible for discrepancies observed in I-V characteristics (see Ref. [2]).     

基于附加虚拟支座的结构损伤识别方法

本文针对土木工程中实测模态相对较少,很难进行大型结构的损伤识别的困难,提出附加虚拟支座的损伤识别方法。该方法利用约束子结构方法在结构上附加虚拟支座来增加结构形式的方法,增加识别模态的数量,从而实现结构的准确损伤识别。约束子结构方法的基本思想是通过响应的卷积组合为零将传感器转化为虚拟支座。将附加虚拟支座后的结构定义为虚拟结构,每个虚拟支座对应一个虚拟结构,那么在结构上不同位置附加虚拟支座,则可以获得多个虚拟结构的模态;联合所有虚拟结构和对应的频率即可准确快速的识别出整体结构的损伤。最后通过三层空间框架模型验证方法的有效性。     

联合整体和局部动态信息的空间桁架模型修正试验

由于土木工程结构的复杂性、传感器测点的有限性以及局部损伤的不敏感性等问题,大型结构的模型修正存在一定困难。针对空间桁架结构,为克服上述问题,对其进行整体和局部的动力测试试验,然后联合实测的结构整体和局部动态信息进行模型修正：首先进行空间桁架整体的动力测试试验,获得反应整体特性的低阶模态;然后为了提高局部杆件的动态特性,在杆件上附加一定质量,获得附加质量后杆件的局部主频率,并在各类杆件中选取一定数目进行动态测试;最后联合所有实测结构整体的低阶模态和杆件的局部主频率,对空间桁架结构进行模型修正。修正后的模态参数与实测模态吻合良好,验证了方法的有效性。     

Olefin Metathesis on a TLC Plate as a Tool for a High‐Throughput Screening of Catalyst‐Substrate Sets

A methodology for screening either various catalysts for a given metathesis reaction, i.e., ring opening‐ring closing alkene metathesis (RO‐RCM) and cross‐metathesis (CM), or various substrates for a given pre‐catalyst on a thin layer chromatography (TLC) plate has been developed. As the substrates elute with the solvent, this TLC‐based system acts as a heterogeneous catalyst bed (“TLC reactor”). Selected promising catalyst candidates were screened on a TLC plate and their initial catalytic potential as observed in the TLC test was later fully confirmed in a classical heterogeneous reaction set‐up using standard commercially available silica (D11‐10). Reacting polyfunctional, natural product‐like substrates in our TLC reactor allows the simultaneous screening of various substrates and the convenient micro‐scale preparation and isolation of potentially biologically active products.     

Dynamics of Fusarium Mycotoxins and Lytic Enzymes during Pea Plants’ Infection

Fusarium species are common plant pathogens that cause several important diseases. They produce a wide range of secondary metabolites, among which mycotoxins and extracellular cell wall-degrading enzymes (CWDEs) contribute to weakening and invading the host plant successfully. Two species of Fusarium isolated from peas were monitored for their expression profile of three cell wall-degrading enzyme coding genes upon culturing with extracts from resistant (Sokolik) and susceptible (Santana) pea cultivars. The extracts from Santana induced a sudden increase in the gene expression, whereas Sokolik elicited a reduced expression. The coherent observation was that the biochemical profile of the host plant plays a major role in regulating the fungal gene expression. In order to uncover the fungal characteristics in planta, both pea cultivars were infected with two strains each of F. proliferatum and F. oxysporum on the 30th day of growth. The enzyme activity assays from both roots and rhizosphere indicated that more enzymes were used for degrading the cell wall of the resistant host compared to the susceptible host. The most commonly produced enzymes were cellulase, β-glucosidase, xylanase, pectinase and lipase, where the pathogen selectively degraded the components of both the primary and secondary cell walls. The levels of beauvericin accumulated in the infected roots of both cultivars were also monitored. There was a difference between the levels of beauvericin accumulated in both the cultivars, where the susceptible cultivar had more beauvericin than the resistant one, showing that the plants susceptible to the pathogen were also susceptible to the toxin accumulation.