Detecting flaws in concrete blocks using the impact-echo method

The objectives of this paper are to investigate the impact response of concrete blocks and to study the feasibility of using the impact-echo method for detection of flaws in concrete blocks. Numerical studies were carried out to acquire the transient responses of intact concrete blocks subjected to impact. In addition, the impact responses of concrete blocks containing flaws were explored. Numerical results were verified by experimental studies on concrete blocks with/without flaws. It is shown that the impact response of a concrete block is composed of frequencies corresponding to the modes of vibration of the block. Among these frequencies, there is a predominant frequency and its value depends on the geometry and dimensions of the block for a given P-wave speed in concrete. It is also shown that the presence of a flaw disrupts the modes of vibration. A shift of the predominant frequency to a lower value is a key indication of the presence of the flaw. In addition, multiple wave reflections between the impact surface and the surface of the flaw produce a large amplitude peak in the spectrum at the frequency corresponding to the depth of the flaw. (c) 2007 Elsevier Ltd. All rights reserved

Back-calculation of concrete pavement modulus using road-rater data

This paper deals with the back-calculation of elastic modulus of jointed concrete pavement. A series of road-rater tests are carried out on a jointed, Portland cement concrete (PCC) pavement of a partially completed freeway in Taiwan. The deflection data obtained with a road rater are used to back-calculate the modulus of elasticity of the PCC pavement and the coefficient of subgrade reaction. The back-calculation is done using BACK, a computer program developed based on the plate theory. The validity of the BACK program is verified with measured deflections, as well as predictions by ILLISLAB, an existing finite element code that has been proven reliable in predicting pavement responses. The results of this study show that the BACK program is quite reliable in predicting the elastic modulus of PCC pavement and the coefficient of subgrade reaction. However, the results are based on the analysis of PCC pavement over a granular subgrade and may not be directly applicable to those over asphalt-stabilized subbases

The unconventional doping in YBa2Cu3O7−x/La0.7Ca0.3MnO3 heterostructures by termination control

In strongly correlated oxides, heterostructures provide a powerful route to manipulate the charge, spin, orbital, and lattice degrees of freedom to create distinctive functionalities. In this work, we have achieved atomically precise interface control in YBa2Cu3O7−x/La0.7Ca0.3MnO3 (YBCO/LCMO) heterostructures and find a hidden effective doping. This mechanism is responsible for higher Tc in the sample with the MnO2-terminated interface than in that with the La0.7Ca0.3O-terminated interface. The MnO2-terminated sample also shows a larger magnetic moment of Mn together with a lower valence state. For more than a decade, the control of Tc in these heterostructures prior to this work has been solely via the variation of YBCO or LCMO thickness. This work hints at an alternative way of exploiting and exploring the interactions between superconductivity and magnetism in this system

Adaptive Tunning of All Parameters in a Multi- Swarm Particle Swarm Optimization Algorithm : An Application to the Probabilistic Traveling Salesman Problem

One of the main issues in the application of a Particle SwarmOptimization (PSO) algorithm and of every evolutionary opti-mization algorithm is the finding of the suitable parameters ofthe algorithm. In this paper, we use a parameter free version of aMulti-Swarm PSO algorithm where random values are assignedin the initialization of all parameters (including the number ofswarms) of the algorithm and, then, during the iterations theparameters are optimized together and simultaneously with theoptimization of the objective function of the problem. This ideais used for the solution of the Probabilistic Traveling SalesmanProblem (PTSP). The PTSP is a variation of the classic Trav-eling Salesman Problem (TSP) and one of the most significantstochastic routing problems. In the PTSP, only a subset of poten-tial customers needs to be visited on any given instance of theproblem. The number of customers to be visited each time is arandom variable. The proposed algorithm is tested on numer-ous benchmark problems from TSPLIB with very satisfactoryresults. It is compared with other algorithms from the literature,and, mainly with a Multi-Swarm Particle Swarm Optimizationwith parameters calculated with a classic trial - and - error pro-cedure and they are the same for all instances.Godkänd; 2014; 20141124 (athmig