Air-Coupled Surface Wave Transmission Measurement Across A Partially Closed Surface-Breaking Crack In Concrete

Previous researchers have demonstrated that the transmission of surface waves is effective to estimate the depth of a surface-breaking crack in solids. However, most of the results were obtained using a well-defined crack (or notch) in laboratory. In fact, there is a critical gap to apply the theory to surface-breaking cracks in concrete structures subjected to external loadings where the cracks are generally ill-defined, and partially closed. In this study, the authors investigated transmission coefficients of surface waves across a partially closed surface-breaking crack in concrete subjected to monotonically increasing compressive loadings. First, a concrete beam (0.5 X 0.154 X 2.1 m(3)) having two surface-breaking cracks with various crack widths was prepared in laboratory. Second, transmission coefficients of impact-induced surface waves were measured across a surface-breaking crack in the concrete beam with increasing compressive loadings from 0 to 140kN (10% of the ultimate compressive strength of the concrete beam). External post-tensioning was used to apply the compression. For comparison purpose, sensitivity of surface wave velocity to compressive loading was also investigated. As a result, observations in this study reveal that transmission coefficient is a more sensitive acoustic parameter than phase velocity to evaluate a surface-breaking cracking in concrete subjected to compressive loadings.Civil, Architectural, and Environmental Engineerin

Nematicity as a route to a magnetic field-induced spin density wave order; application to the high temperature cuprates

The electronic nematic order characterized by broken rotational symmetry has been suggested to play an important role in the phase diagram of the high temperature cuprates. We study the interplay between the electronic nematic order and a spin density wave order in the presence of a magnetic field. We show that a cooperation of the nematicity and the magnetic field induces a finite coupling between the spin density wave and spin-triplet staggered flux orders. As a consequence of such a coupling, the magnon gap decreases as the magnetic field increases, and it eventually condenses beyond a critical magnetic field leading to a field-induced spin density wave order. Both commensurate and incommensurate orders are studied, and the experimental implications of our findings are discussed.Comment: 5 pages, 3 figure

A model on knowledge and endogenous growth

The authors present a model of endogenous growth in which the main engine of economic development is knowledge. Using a two-sector closed economy model that comprises of a conventional goods-producing sector and a research and development sector, their model incorporates two key aspects of knowledge: technology and human capital. Steady-state equilibrium conditions show that the growth rate of per capita income hinges on the growth rate of human capital. While the growth rate of human capital has been previously shown to affect the growth of the economy in transition between steady states or balanced growth paths, the authors are the first to link the growth rate of human capital to the steady-state growth rate of productivity and output per worker. Furthermore, this result does not exhibit scale effects or policy invariance, both of which have been longstanding concerns with the predictions of endogenous growth models developed in the 1990s.Economic Growth,Achieving Shared Growth,Economic Theory&Research,Governance Indicators,Health Monitoring&Evaluation