A numerical investigation on the damage identification of timber utility poles based on wavelet packet energy

Timber utility poles are traditionally used for electricity and telecommunication distribution. Due to the old age of many distribution networks, the health condition of these timber poles needs to be assessed. Non-destructive testing (NDT) methods based on stress wave propagation have successfully been used in practice for the condition assessment of timber poles. However, for the successful application of these methods for damage identification, some limitations exist. To overcome these limitations, this paper proposes the use of wavelet packet energy (WPE) for the stress wave data analysis and damage identification. WPE is a sensitive indicator for structural damage and has been used for damage detection in various types of structures. This paper presents a comprehensive investigation on the novel use of WPE for the damage identification in timber utility poles using finite element (FE) models. The research study comprises of the following investigations: i) a comparative study between 2D and 3D models, ii) a sensitivity study of mesh density for 2D models, and iii) a study of the novel WPE-based technique for damage detection in timber poles. The results of the new method clearly show the effectiveness of the proposed damage identification technique based on WPE

Provision of reinforcement in concrete solids using the generalized genetic algorithm

A generalized genetic algorithm has been developed to find the global optimal reinforcement contents for a concrete solid structure subjected to a general three-dimensional (3D) stress field. Feasible solutions were examined based on the genetic algorithm, and the heterogeneous strategy used ensures that all of the local optimal regions are searched and the most optimal reinforcement content found. The effectiveness of the proposed approach has been validated by comparing the steel contents evaluated using the present method with those obtained from other available methods. A more economic design is achieved by the proposed algorithm. The method developed provides the designer with a valuable tool for the determination of reinforcements in complicated solid concrete structures. © 2011 American Society of Civil Engineers.postprin

A Semi-analytical Model for Remote Sensing Retrieval of Suspended Sediment Concentration in the Gulf of Bohai, China

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A pore-expanded supramolecular organic framework and its enrichment of photosensitizers and catalysts for visible-light-induced hydrogen production

A pore-expanded three-dimensional supramolecular organic framework SOF-bpb, with a previously unattained aperture size of 3.6 nm, has been constructed in water from the co-Assembly of cucurbit[8]uril (CB[8]) and a tetraphenylmethane-cored 1,4-bis(pyridin-4-yl)-benzene-Appended building block M1. The periodicity of SOF-bpb in water and in the solid state has been confirmed using synchrotron X-ray scattering and diffraction experiments. SOF-bpb can adsorb anionic and neutral Ru complex photosensitizers and anionic Wells-Dawson-Type and Keggin-Type polyoxometalates (POMs). The adsorption leads to an important enrichment effect, which remarkably increases the catalytic efficiency of the Ru complex-POM systems for visible light-induced reduction of protons to produce H . The expanded aperture of SOF-bpb also facilitates light absorption of the adsorbed Ru complex photosensitizers and electron transfer between excited complexes and the POM catalysts, leading to enhanced photocatalytic activities as compared with the prototypical SOF that has an aperture size of 2.1 nm. 2+ 2+ 2+

Recent progress of mesoporous silica materials

Since the synthesis of novel mesoporous silica materials in 1992, the materials have become a great demand in many research fields. The authors reviewed the synthesis of mesoporous silica materials and their classification, their formation mechanism, as well as the aspects of controlling porosity and recent progresses of their applications. The mesoporous silica materials may be found great utility in catalysis and nano-technology etc

Verticalization of bacterial biofilms

Biofilms are communities of bacteria adhered to surfaces. Recently, biofilms of rod-shaped bacteria were observed at single-cell resolution and shown to develop from a disordered, two-dimensional layer of founder cells into a three-dimensional structure with a vertically-aligned core. Here, we elucidate the physical mechanism underpinning this transition using a combination of agent-based and continuum modeling. We find that verticalization proceeds through a series of localized mechanical instabilities on the cellular scale. For short cells, these instabilities are primarily triggered by cell division, whereas long cells are more likely to be peeled off the surface by nearby vertical cells, creating an "inverse domino effect". The interplay between cell growth and cell verticalization gives rise to an exotic mechanical state in which the effective surface pressure becomes constant throughout the growing core of the biofilm surface layer. This dynamical isobaricity determines the expansion speed of a biofilm cluster and thereby governs how cells access the third dimension. In particular, theory predicts that a longer average cell length yields more rapidly expanding, flatter biofilms. We experimentally show that such changes in biofilm development occur by exploiting chemicals that modulate cell length.Comment: Main text 10 pages, 4 figures; Supplementary Information 35 pages, 15 figure

Effect of Ti-doping on the framework Structure of Mesoporous silica

The Ti-doped mesoporous silica MCM-41 materials were synthesized under basic condition at room temperature. The characteristics of samples were investigated by using XRD, HREM, IR, and N-2 adsorption techniques. The results show that Ti ions can get into the Si frame work and lead to the vibration of Si-O-Ti bond, with the increase of Ti ion addition, the mesoporous silica framework structure can be disordered and finally deteriorated

Synthesis of ordered mesoporous aluminosilicate under a low surfactant/silica molar ratio condition

Ordered mesoporous aluminosilicate materials with atomic Si/Al ratios of 16 similar to 64 were synthesized at a very low molar ratio of surfactant/silica (0.12) by using aluminium chloride hexahydrate and TEOS as the sources of aluminium and silicon. The resulting materials were characterized by XRD, TEM, FTIR and nitrogen sorption. As the NaOH/Si molar ratio increases from 0.2 to 0.6, the products obtained change from hexagonal MCM-41 to cubic MCM-48. The quality of the product rapidly deteriorates as the aluminium content of the solid increases beyond a certain limit. XRD shows that the substitution of the silicon by the large aluminium atoms leads to the expansion of the unit cell

Study on the synthesis and mechanism of mesoporous silica with hexastyle structure

The mesoporous silica MCM-41 materials with hexastyle structure were synthesized under strongly acidic condition. The characteristics of samples were investigated by using XRD, N-2 adsorption, HREM, and SEM techniques. The results show that MCM-41 powder with hexastyle structure, which is wormlike in micrometer-scale, consists of thousands of mesoporous channels in nano-scale. The morphogenesis of hexastyle mesoporous silica is due to the accretion of surfactant micella combined with silica oligmers in the low concentration of TEOS