A comparative study of guided wave propagation in timber poles with isotropic and transversely isotropic material models

Guided wave (GW) has been used for many years in non-destructive testing (NDT). There are various ways to generate the guided wave, including impact or impulse either manually or using devices. Although the method of impact or impulse is considered to be simple and practical in guided wave generation, it produces waves with broadband frequencies, which often make analysis much more difficult. The frequency bandwidth produced by manual impacts is usually at the low end, and is therefore justified when dealing with one dimensional wave propagation assumption in low strain integrity testing of cylindrical structures. Under such assumption if the velocity is known accurately, NDTs can produce reasonably good results for the condition assessment of the structure. However, for guided wave propagation in timber pole-like structures, it is rather complicated as timber is an orthotropic material and wave propagation in an orthotropic medium exhibits different characteristics from that in isotropic medium. It is possible to obtain solutions for guided wave propagation in orthotropic media for cylindrical structures, even though the orthotropic material greatly complicates GW propagation. In this paper, timber has been considered as a transversely isotropic (i.e. simplified orthotropic) material and a comparative study of GW propagation in a timber pole is conducted considering isotropic and transversely isotropic modelling. Phase velocity, group velocity and attenuation are the main parameters for this comparative study. Moreover, tractionfree situation and embedded geotechnical condition are also taken into consideration to evaluate the effect of boundary. Displacement profile, wave propagation pattern and power flow at particular frequency are utilized to determine different displacement components of longitudinal and flexural waves along and across the timber pole. Effect of temperature and moisture content (in terms of modulus of elasticity) in timber pole is also compared to show the variation in phase velocity.

Retinal sensitivity loss in third-generation n-3 PUFA-deficient rats

A previous study conducted in guinea pigs suggested that ingestion of diets high in EPA and DHA may result in suboptimal retinal function. The aim of the present study was to evaluate retinal function in pigmented (Long-Evans) rats, raised to a third generation on diets that were either deficient in n-3 PUFA or adequate (with the addition of DHA). Electroretinographic assessment employed full-field white flash stimulation. Photoreceptor responses were evaluated in terms of peak amplitudes and implicit times (a-wave, b-wave), intensity-response functions (Naka-Rushton), and the parameters of a model of transduction (P3). Retinal phospholipid FA composition was measured by capillary GLC. DHA levels were reduced by 55% in n-3-deficient animals compared with the n-3-adequate group, whereas the levels of docosapentaenoic acid n-6 were 44 times higher in n-3-deficient animals. The level of arachidonic acid was marginally higher (12.8%) in n-6-adequate animals. The n-3-deficient animals exhibited significantly reduced retinal sensitivity (σ and S values were both affected by 0.29 log units) and increased b-wave implicit times compared with those fed the n-3-adequate diet. These data suggest that n-3 PUFA are required for development of retinal sensitivity, more so than other indices of retinal function assessed by current methods, such as maximal response amplitude. However, the benefit for retinal function of adding preformed DHA to diets already replete in n-3 PUFA remains unclear.

Combined continuous wave and pulsed plasma modes : For more stable interfaces with higher functionality on metal and semiconductor surfaces

A novel approach to producing improved bio-interfaces by combining continuous wave (CW) and pulsed plasma polymerization (PP) modes is reported. This approach has enabled the generation of stable interfaces with a higher density of primary amine functionality on metal, ceramic and semiconductor surfaces. Heptylamine (HA) was used as the amine-precursor. In this new design, a thin CW PPHA layer is introduced to provide strong cross-linking and attachment to the metal or semiconductor surfaces and to provide a good foundation for better bonding a pulsed PPHA layer with high retention of functional groups. The combined mode provides the pulsed mode advantage of a 3-fold higher density of primary amines, while retaining much of the markedly higher stability in aqueous solutions of the continuous mode.

A methodology for simulating hydrogen sulphide generation in sewer network using EPA SWMM

Predicting hydrogen sulphide concentration in sewer network through modelling tools will be beneficial for many stakeholders to design appropriate mitigation strategies. However, the hydrogen sulphide modelling in a sewer network is crucially dependent on the hydraulic modelling of the sewer. The establishment of precise hydrogen sulphide and hydraulic modelling however requires detailed and accurate information about the sewer network structure and the model parameters. This paper outlines a novel approach for the development of hydraulic and hydrogen sulphide modelling to predict the concentration of hydrogen sulphide in sewer network. The approach combines the calculation of wastewater generation and implementation of flow routing on the EPA SWMM 5.0 platform to allow hydrodynamic simulations. Dynamic wave routing is used for hydraulic simulations. It is considered to be the best approach to route existing/old sewer flow. The build-up of hydrogen sulphide model includes the empirical models of hydrogen sulphide generation and emission. Trial of the model was conducted to simulate a sewer network in Seoul, South Korea with some hypothetical data. Further analysis on the use of chemical dosing on the sewer pipe was also performed by the model. Promising results have been obtained through the model, however calibration and validation of the model is required. The presented methodology provides a possibility of the free platform SWMM to be used as a prediction tool of hydrogen sulphide generation. © 2014 © 2014 Balaban Desalination Publications. All rights reserved.