A new mechanical structural damage feature index based on HHT

A new damage feature index is presented for the structural health monitoring based on Hilbert-Huang transform (HHT). The energy marginal spectrum of the dynamic signal is used to construct damage characteristic parameter, which can reflect the signal energy variation and benefit the structural damage detection. A sinusoidal wave with frequency change and a composite plate vibration experiment with pre-defined damage are designed to verify the effectiveness of characteristic parameter in damage detection. Results obtained from simulation and test show that the extracted non-model-based damage feature index is available and sensitive in damage detection of time-varying system.Peer Reviewe

What Causes the Volatility of the Balancing Item?

This paper analyzes the impacts of timing errors, capital flows and economic openness on the behavior of the balancing item. We choose Norway, Sweden, Philippines and South Africa as sample countries where the size of the balancing item is often excess the IMF's criterion of ‘smallness'. The empirical results show that the sources of the volatility of the balancing item are different among these four countries.Balancing item, Balance of payments

Dialkylaluminium 2-imidazolylphenolates: Synthesis, characterization and ring-opening polymerization behavior towards lactides

The stoichiometric reaction of the 2-imidazolylphenols (L1–L9) with the trialkylaluminium reagents AlR₃ (R = Me, Et and iBu), afforded the corresponding dialkylaluminium 2-imidazolylphenolate complexes [R₂Al(L1–L9)] (C1–C11), which were characterized by ¹H/¹³C NMR spectroscopy and by elemental analysis. The molecular structures of the representative complexes C1, C2, C4, C6 and C11 were determined by single-crystal X-Ray diffraction, and revealed a distorted tetrahedral geometry at aluminum. These dialkylaluminium 2-imidazolylphenolates (C1–C11) could efficiently catalyze the ring-opening polymerization of lactides to afford high molecular weight polylactide, both in the presence and absence of BnOH, and as such represent rare examples of the use of bi-dentate ligation at aluminum in such lactide polymerization systems. On the basis of the polymerization results for l-lactide, d-lactide and rac-lactide, the nature of the ligands and the aluminum bound alkyls were found to significantly affect the catalytic activity as well as the properties of the resultant polylactides

Stochastic modelling of hygrothermal performance of highly insulated wood framed walls

Recent years, the majority of building codes in North America require an energy efficient envelope to improve the building energy efficiency. There are different design strategies to achieve a higher insulation level of the wood framed building envelope, such as increasing the depth of stud cavity to accommodate thicker insulation or adding an exterior insulation while keeping the depth of stud cavity unchanged. However, the highly insulated walls may lead to a higher risk of moisture problems. The deep cavity walls will reduce the temperature of the wood sheathing, which may increase the potential for condensation and mold growth. The exterior insulated walls may result in a low drying capacity of the wood sheathing if the exterior insulation has a low vapour permeance. Although hygrothermal simulations have been widely used to investigate the moisture performance of wood framed walls, the uncertainty of the input parameters may lead to discrepancies between simulation results and real performance of the walls. This paper investigates the hygrothermal performance of highly insulated wood framed walls- deep cavity wall and exterior insulated wall using a stochastic simulation approach. The uncertainties of the input parameters including the material properties, air leakage and rain leakage rates are taken into account in stochastic modelling. The mold growth risks of the walls are evaluated based on the stochastic simulation results

The next-to-next-to-leading order soft function for top quark pair production

We present the first calculation of the next-to-next-to-leading order threshold soft function for top quark pair production at hadron colliders, with full velocity dependence of the massive top quarks. Our results are fully analytic, and can be entirely written in terms of generalized polylogarithms. The scale-dependence of our result coincides with the well-known two-loop anomalous dimension matrix including the three-parton correlations, which at the two-loop order only appear when more than one massive partons are involved in the scattering process. In the boosted limit, our result exhibits the expected factorization property of mass logarithms, which leads to a consistent extraction of the soft fragmentation function. The next-to-next-to-leading order soft function obtained in this paper is an important ingredient for threshold resummation at the next-to-next-to-next-to-leading logarithmic accuracy.Comment: 34 pages, 9 figures; v2: added references, matches the published versio