fGAAM: A fast and resizable genetic algorithm with aggressive mutation for feature selection

Pattern Analysis and Applications - The paper introduces a modified version of a genetic algorithm with aggressive mutation (GAAM) called fGAAM (fast GAAM) that significantly decreases the time...     

Strain-rate sensitivity of strength in macro-to-micro-to-nano crystalline nickel

The mechanical behavior of nickel is evaluated over eight-orders of magnitude change in strain rate to see if the change in strain-rate sensitivity exponent is affected by the grain size decreasing from the micron to nanoscale range. Tensile testing is used to measure the strain-rate dependence of the tensile strength on the grain size in crystalline nickel foils. Micro-scratch testing is used to determine the strain-rate dependence of the scratch hardness variation with scratch velocity. It is found that the mechanical test results can be directly compared. The increase in the strain-rate sensitivity exponent that is found with increasing strain rate is slower for nanocrystalline than for microcrystalline nickel foils where strength values begin to converge at the highest strain rates.     

Simultaneous identification of moving masses and structural damage

A method for simultaneous identification of moving masses and damages of the supporting structure from measured responses is presented. The interaction forces between the masses and the structure are used as excitation. Masses and damage extents are used as the optimization variables; compared to the approaches based on identification of the interaction forces, it allows ill-conditioning to be avoided and decreases the number of required sensors. The virtual distortion method is used; the damaged structure is modeled by the intact structure subjected to response-coupled virtual distortions and moving forces. These are related to the optimization variables via a linear system, which allows the optimization variables of both kinds to be treated in a unified way. A moving dynamic influence matrix is introduced to reduce the numerical costs. The adjoint variable method is used for fast sensitivity analysis. A numerical experiment of a three-span beam with 10% rms measurement error and three types of model errors is presented.     

Experimental assessment of CFRP reinforced wooden beams by 4-point bending tests and photoelastic coating technique

The article presents selected results of experimental investigations into carbon fibre reinforced plastic (CFRP) strips for strengthening wooden beams. About 100 years old beams were tested under four-point bending load. Electrical-resistance strain gauges (ERSG) together with the photoelastic coating technique (PCT) were used to determine strain distributions (also in the inserted strips). A comparison of the strain values measured by, respectively, ERSG and PCT showed significant differences (amounting to 2.2–72.5%) due to the different character of the two kinds of measurement, connected with the significant effect of wood structure on local strain distributions. Generally, the strain measurement results suggest that the proposed methods of reinforcing wooden beams with CFRP strips are useful for restoration purposes. The effectiveness of the reinforcement significantly depends on the quality of the wood-CFRP strip bond, which means the preparation of the surfaces for bonding plays an important role.     

Hand exposure in nuclear medicine workers

As a result of the gamma radiation emitted by radioactive elements (e.g. 99mTc and 131I) used in nuclear medicine laboratories for diagnostic and therapeutic purposes, nuclear medicine workers are exposed to whole-body doses. These doses arc usually measured by using individual film dosemeters. Lead or lead glass shields used during the handling of radioisotopes minimise the whole-body doses received. Nevertheless, part of the job has to be performed manually, hence the hands are more exposed to radiation. This paper presents the results of measuring the equivalent dose to the hands of workers employed in five selected nuclear medicine laboratories where technetium and iodine radioisotopes are in common use. Sixty workers, including physicians, nurses, radiopharmacists and technicians, were included in the study. Doses were measured at 1 month intervals. The study indicated that, in some instances, the danger of radiation dose to the hand may be significant. Monthly doses exceeded 50 mSv, which may suggest that an annual dose may be higher than 500 mSv.     

Substructure isolation and damage identification using free responses

Structural health monitoring (SHM) has become a hot and intensively researched field in civil engineering. Thereinto, damage identification play an important role in maintaining structural integrity and safety. Many effective methods have been proposed for damage identification. However, accurate global identification of large real-world structures is not easy due to their complex and often unknown boundary conditions, nonlinear components, insensitivity of global response to localized damages, etc. Furthermore, global identification often requires lots of sensors and involves large number of unknowns. This is costly, rarely feasible in practice, and usually yields severely ill-conditioned identification problems. Substructuring approach is a possible solution: substructuring methods can focus on local small substructures; they need only a few sensors placed on the substructure and yield smaller and numerically much more feasible identification problems. This paper proposed an improved substructure method using local free response for substructure damage identification. The virtual supports are constructed by Substructure Isolation Method (SIM) using the linear combination of the substructural responses. The influence of the global errors is isolated by adding the virtual supports on the main degree of freedoms (DOFs) of the substructure. Through the correlation analysis, the substructural modes are selected and used for damage identification of the substructure. A plain model of cable stayed bridge is used for the verification of the proposed method.