Efficiency of nearly periodic structures for mitigation of ground vibration

Periodic structures are known to produce passbands and stopbands for propagation of vibration energy within the frequency domain. Sources vibrating harmonically at a frequency within a passband can lead to propagation of energy through propagating modes over long distances. However, sources vibrating at a frequency within a stopband excite only nearfields in the form of attenuating and evanescent modes, and the energy decays with distance. The decay phenomena are due to destructive interference of waves reflected and scattered by interfaces or obstacles placed periodically within or between the repeated cells of the structure. For a truly periodic structure, the vibration level within a stopband goes toward zero after infinitely many repetitions of the cell. For example, employing a two-dimensional model, Andersen [1] found that stopbands for ground vibration in the low-frequency range can be introduced by periodic inclusions or changes to the ground surface geometry. However, for vibration mitigation in the context of real civil-engineering problems related to ground-borne noise from railways, for example, the excitation is not strictly harmonic and a steady state of the response is usually not achieved. Further, only a limited number of repetitions of wave impedance blocks or barriers can be made in practice, and in three dimensions, the inclusions have finite extent in the direction orthogonal to the array. Similarly to the work by Andersen et al. [2], this paper addresses the question whether repeated structures of nearly periodic nature can be used to mitigate vibrations caused by non-stationary sources. For this purpose, wave impedance blocks with finite numbers of repetitions are compared to their truly periodic counterparts. Firstly, a two-dimensional study is conducted with focus on studying the nature of wave modes in a periodic array of wave impeding blocks. Secondly, three-dimensional analysis is performed in the frequency domain, focusing on the insertion loss provided by increasing numbers of repetitions of blocks with different height and embedment. Finally, the insertion loss provided by nearly periodic structures is examined, and the mitigation efficiency of wave-impeding-block arrays is quantified in the case of transient loads

Environmental vibration reduction utilizing an array of mass scatterers

© 2017 The Authors. Published by Elsevier Ltd. Ground vibration generated by rail and road traffic is a major source of environmental noise and vibration pollution in the low-frequency range. A promising and cost effective mitigation method can be the use of heavy masses placed as an array on the ground surface near the road or track (e.g. concrete or stone blocks, specially designed brick walls, etc.). This work concerns the effectiveness of such blocking masses. A semi-analytical lumped-parameter method is utilized, assuming that the blocks are point masses situated on an elastic half-space. The work is enhanced by examples highlighting advantages and disadvantages of single-mass scatterers and multiple-mass scatterers

Identification of Pathogenicity-Related Genes in the Vascular Wilt Fungus Verticillium dahliae by Agrobacterium tumefaciens-Mediated T-DNA Insertional Mutagenesis

Verticillium dahliae is the causal agent of vascular wilt in many economically important crops worldwide. Identification of genes that control pathogenicity or virulence may suggest targets for alternative control methods for this fungus. In this study, Agrobacteriumtumefaciens-mediated transformation (ATMT) was applied for insertional mutagenesis of V. dahliae conidia. Southern blot analysis indicated that T-DNAs were inserted randomly into the V. dahliae genome and that 69% of the transformants were the result of single copy T-DNA insertion. DNA sequences flanking T-DNA insertion were isolated through inverse PCR (iPCR), and these sequences were aligned to the genome sequence to identify the genomic position of insertion. V. dahliae mutants of particular interest selected based on culture phenotypes included those that had lost the ability to form microsclerotia and subsequently used for virulence assay. Based on the virulence assay of 181 transformants, we identified several mutant strains of V. dahliae that did not cause symptoms on lettuce plants. Among these mutants, T-DNA was inserted in genes encoding an endoglucanase 1 (VdEg-1), a hydroxyl-methyl glutaryl-CoA synthase (VdHMGS), a major facilitator superfamily 1 (VdMFS1), and a glycosylphosphatidylinositol (GPI) mannosyltransferase 3 (VdGPIM3). These results suggest that ATMT can effectively be used to identify genes associated with pathogenicity and other functions in V. dahliae

Effect of modelling the air in rooms on the prediction of vibration transmission in cross-laminated timber buildings

Timber buildings are intrinsically lightweight and hence can be susceptible to low-frequency vibrations and structure-borne noise. So, within the development of technical solutions for mitigating unwanted vibrations and noise, accurate and computationally efficient numerical models are considered to be of great value. Such models should take into account all physical phenomena that are relevant for achieving adequate accuracy in predictions, while not being overly detailed so that the computational efficiency is impaired. In this paper, the necessity of modelling the enclosed air in room volumes of buildings made of cross-laminated timber, with respect to the prediction of vibration transmission, is investigated. Coupled structural-acoustic finite element analysis is employed for an example building structure. It is found that modelling the air in the receiver room, i.e. in the room where the vibration response is evaluated, has a marked effect on the vibration transmission between panels

Materials identification using a small-scale pixellated x-ray diffraction system

A transmission x-ray diffraction system has been developed using a pixellated, energy-resolving detector (HEXITEC) and a small-scale, mains operated x-ray source (Amptek Mini-X). HEXITEC enables diffraction to be measured without the requirement of incident spectrum filtration, or collimation of the scatter from the sample, preserving a large proportion of the useful signal compared with other diffraction techniques. Due to this efficiency, sufficient molecular information for material identification can be obtained within 5 s despite the relatively low x-ray source power. Diffraction data are presented from caffeine, hexamine, paracetamol, plastic explosives and narcotics. The capability to determine molecular information from aspirin tablets inside their packaging is demonstrated. Material selectivity and the potential for a sample classification model is shown with principal component analysis, through which each different material can be clearly resolved