Structural oscillation modes identification by applying controlled loads and using microwave interferometry

Radar interferometry, capable of remote detection of displacements and deformations of a structure, has been successfully experimented in a number of case studies. Radar interferometry offers high-speed range imaging and range displacement measurement capability, but it lacks in the identification of the different kinds of modes usually excited in a dynamic test. In this paper an approach to the measurement capable of identifying bending and torsional oscillation modes is described. The basic idea rely on the application of suitable loads to the structure under test in order to cause controlled changes of its frequency response. The results of such a dynamic test, performed on a canopy, are reported.     

Model building and assessment of the impact of covariates for disease prevalence mapping in low-resource settings: to explain and to predict

This paper provides statistical guidance on the development and application of model-based geostatistical methods for disease prevalence mapping. We illustrate the different stages of the analysis, from exploratory analysis to spatial prediction of prevalence, through a case study on malaria mapping in Tanzania. Throughout the paper, we distinguish between predictive modelling, whose main focus is on maximizing the predictive accuracy of the model, and explanatory modelling, where greater emphasis is placed on understanding the relationships between the health outcome and risk factors. We demonstrate that these two paradigms can result in different modelling choices. We also propose a simple approach for detecting over-fitting based on inspection of the correlation matrix of the estimators of the regression coefficients. To enhance the interpretability of geostatistical models, we introduce the concept of domain effects in order to assist variable selection and model validation. The statistical ideas and principles illustrated here in the specific context of disease prevalence mapping are more widely applicable to any regression model for the analysis of epidemiological outcomes but are particularly relevant to geostatistical models, for which the separation between fixed and random effects can be ambiguous.     

Application of the European flaw assessment procedure SINTAP to thin wall structures subjected to biaxial and mixed mode loadings

A recently proposed slightly modified version of the European flaw assessment procedure SINTAP for thin wall structures has been applied to another 35 thin sheets made of two different aluminium alloys and two ferritic steels. The specimens were subjected to biaxial and mixed mode loadings. It is shown that the method allows predictions of the load versus crack extension characteristics with acceptable conservatism.     

Rehabilitation of reinforced concrete axially loaded elements with polymer-modified cementicious mortar

The aim of the paper is to investigate the compatibility and the efficiency of the rehabilitation intervention on reinforced concrete columns with polymer-modified cementicious mortar. This paper presents the results of experimental tests on axial behaviour of reinforced concrete columns, with square cross-section, repaired by polymer-modified cementicious mortar. Tests were repeated varying repair thickness, which included or did not include the steel reinforcement on one face of the square column. Despite this type of intervention is quite common in practice, the effect of repair thickness on the intervention efficiency, in relation to the existing steel reinforcement configuration, had not been previously studied in detail for axially loaded elements.Results were discussed and compared with those from control columns, which were tested in non-damaged, non-repaired conditions. The main findings of this work can be summarized as follows. The repair cannot restore the load-bearing capacity of non-damaged control columns, although they give acceptable results. Repairs that include the longitudinal reinforcement show good properties, with stable behaviour, sharing of loads, and plasticization of the material before failure, whereas thin repairs that do not include the reinforcement do not have adequate performance due to premature debonding. Non-linear numerical models also confirmed the different behaviour of the two types of repair.     

Probabilistic treatment of fracture using two failure models

A probabilistic methodology for brittle fracture based on two local failure models is presented. Probabilistic fracture parameters are obtained using a weakest link and a chain-of-bundles formulation. Both models define limiting distributions for the fracture stress described by a two-parameter Weibull distribution. Numerical procedures employing measured toughness data and finite element solutions are also described to calibrate the Weibull parameters. An application of the methodology then follows to predict geometry and stable crack growth effects on the distribution of macroscopic fracture toughness (J_c) for a high-strength steel. Measured fracture toughness values for a high-constraint geometry that exhibit no prior ductile tearing are effectively ‘transferred' to a different geometry having much lower constraint and in which tearing precedes cleavage. The inherent difficulty in predicting the scatter of experimental fracture toughness, as well as constraint and ductile tearing effects, within the scope of conventional procedures appears greatly reduced in the framework presented in this work.     

Efficient FPGA implementation of a STBC-OFDM combiner for an IEEE 802.16 software radio receiver

In this paper, an efficient FPGA implementation of a 4×4 Space-Time Block Coding (STBC) combiner for MIMO-OFDM software radio receivers is considered. The proposed combiner is based on a low-complexity algorithm which reduces the interference due to the Quasi-Orthogonality of the STBC decoding. In the literature, feedback techniques have been proposed to solve this problem. However, the algorithm introduced in this paper has been conceived in order to avoid the transmission feedback, by estimating the interference factors and removing them. The proposed algorithm exhibits a low computational complexity and complies with the requirements of HW feasibility, considering the execution time/area occupation trade-off.     

On multiuser perspectives in passive stereographic virtual environments

The use of stereographic systems is spreading out in modern society, from the revolution of cinematography to its adoption in high‐tech products such as portable gaming devices or photo cameras. However, the fruition of immersive stereographic systems by more than one person at a time is still a research issue. In more detail, the class of passive stereo systems presents technological limitations of displaying correct multiuser perspectives. In fact, the stereo image projected onto the screen is usually rendered according to a unique point of view (PoV). Nevertheless, in multiuser systems, the selection of an appropriate PoV can minimize both optical discomfort and perspective distortion. This paper aims to evaluate which among existing PoV calculation methods provides the best performances in terms of projection realism, optical comfort and overall system usability in multiuser passive stereo systems. The performances have been evaluated in three different “distance” scenarios to take into account also the effects of binocular disparity in the PoV calculation. To accomplish this objective, we administered a questionnaire to nine couple subjects, evaluating each of the investigated PoV calculation methods for each of the three distance scenarios. Copyright © 2013 John Wiley & Sons, Ltd.