Online automatic identification of the modal parameters of a long span arch bridge

The “Infante D. Henrique” bridge is a concrete arch bridge, with a span of 280 m that crosses the Douro River, linking the cities of Porto and Gaia located in the North of Portugal. This structure is being monitored by a recently installed dynamic monitoring system that comprises 12 acceleration channels. This paper describes the bridge structure, its dynamic parameters identified with a previously developed ambient vibration test, the installed monitoring equipment and the software that continuously processes the data received from the bridge through an Internet connection. Special emphasis is given to the algorithms that have been developed and implemented to perform the online automatic identification of the structure modal parameters from its measured responses during normal operation. The proposed methodology uses the covariance driven stochastic subspace identification method (SSI-COV), which is then complemented by a new algorithm developed for the automatic analysis of stabilization diagrams. This new tool, based on a hierarchical clustering algorithm, proved to be very efficient on the identification of the bridge first 12 modes. The results achieved during 2 months of observation, which involved the analysis of more than 2500 datasets, are presented in detail. It is demonstrated that with the combination of high-quality equipment and powerful identification algorithms, it is possible to estimate, in an automatic manner, accurate modal parameters for several modes. These can then be used as inputs for damage detection algorithms.     

Adsorption of Me(II), HEDP, and Me(II)-HEDP onto boehmite at nonstoichiometric Me(II)-HEDP concentrations

In aqueous environments, certain heavy metals are toxic even at very low concentrations. The main pathway of metal removal in the aquatic systems is via adsorption onto surfaces. These are desired processes that help decrease the dissolved fraction of metals in natural water. The presence of organic ligands as mono- and polyphosphonates may produce drastic changes in the mobility of the heavy metals. 1-Hydroxyethane-(1,1-diphosphonic acid) (HEDP) is a very strong chelating agent widely used in industrial applications. This study examines the effect of HEDP on the adsorption of Cu(II), Zn(II), and Cd(II) onto boehmite in nonstoichiometric conditions, with the HEDP concentration higher than the corresponding Me(II) cations. At high surface loading and low pH, HEDP removes Zn(II) and Cd(II) from solution to an appreciable extent. The data are modeled assuming an anionic-ternary complex formation. In the same conditions, Cu(II) adsorption is significantly suppressed at intermediate values of pH, and this behavior is linked to Cu-HEDP complex formation in solution. At low surface covering, the effects of HEDP on metal adsorption are either negligible or slight. This behavior suggests that both ligand and metal are mainly adsorbed in separate form. All experimental data indicate that no changes are observed in the pH edges for phosphonate adsorption. The surface constants to fit the experimental data were calculated by applying the 2-K model constant capacitance (CCM).     

2D natural convection flows in tilted cavities: Porous media and homogeneous fluids

Natural convection flows are studied numerically for porous media and homogeneous fluids inside a rectangular cavity with inclination. These thermal fluid flows are considered under the respective two-dimensional unsteady Boussinesq approximation in stream function and vorticity variables. The study depends on the Rayleigh number, angle of inclination, and the aspect ratio of the cavity. At the validation stage our results are in good agreement with those reported by other authors. Results suppose to be new are presented either for angles of inclination not reported before or for high Rayleigh numbers with large aspect ratios. In rectangular porous cavities with Rayleigh number 10² multiple cells appear for some angles. In homogeneous fluids, for Rayleigh numbers of the order of 10⁵–10⁶ in large enough vertical cavities at most secondary cells appear for some angles and the flow becomes more complex and looks like to be oscillatory.     

Association of indigo with zeolites for improved color stabilization

The durability of an organic color and its resistance against external chemical agents and exposure to light can be significantly enhanced by hybridizing the natural dye with a mineral. In search for stable natural pigments, the present work focuses on the association of indigo blue with several zeolitic matrices (LTA zeolite, mordenite, MFI zeolite). The manufacturing of the hybrid pigment is tested under varying oxidizing conditions, using Raman and ultraviolet-visible (UV-Vis) spectrometric techniques. Blending indigo with MFI is shown to yield the most stable composite in all of our artificial indigo pigments. In the absence of defects and substituted cations such as aluminum in the framework of the MFI zeolite matrix, we show that matching the pore size with the dimensions of the guest indigo molecule is the key factor. The evidence for the high color stability of indigo@MFI opens a new path for modeling the stability of indigo in various alumino-silicate substrates such as in the historical Maya Blue pigment.     

Catalytic properties of cobalt-promoted Pd/HAP catalyst for CO-cleanup of H2-rich stream

The promoting effect of Co addition on the behaviour of the Pd/HAP system in WGS reaction has been investigated. Hydroxyapatite-supported bimetallic PdCo samples have been prepared by two consecutive impregnation steps with solutions of Co and Pd precursors, respectively. The resulting catalysts have been thoroughly characterised by BET, XRD, H₂-TPR, XPS, OSCC and OSC techniques.The progressive addition of cobalt drives to an abundance of the Pd species exhibiting an intimate contact with Co and an eminent enhancement of the redox properties of the Pd/Co(x)/HAP catalysts. This results in an improvement of their performance in WGS reaction. The Pd species presenting an intimate contact with cobalt seems to be the responsible of the improvement of the CO conversion. However, this PdCo interaction leads to an increase in the methanation activity at the expense of WGS activity. When small amounts of O₂ is added to the WGS mixture, the activity is exclusively enhanced in the presence of Co species exhibiting easier reducibility.     

Cactus stem (Opuntia ficus‐indica Mill): anatomy,physiology and chemical composition with emphasis on its biofunctional properties

Cactus stem (Opuntia ficus‐indica Mill) is native to Mesoamerica and marketed in different forms such as fresh, frozen or pre‐cooked. Worldwide, this vegetable is recognized for its pharmaceutical actions, including its antioxidant, diuretic, anticarcinogenic, anti‐inflammatory, anti‐diabetic, and anti‐hypercholesterolemic properties, as well as their antiviral and antispermatogenic effects. However, not all of these properties have been associated with its chemical composition; therefore, this review aims to present and integrate information available on the physiology and anatomy of cactus stem and its chemical composition, focusing on some of the many factors that determine its biofunctionality. © 2017 Society of Chemical Industry