Comparative study between two distinct methods for attenuation correction and the use of no-attenuation correction for the assessment of relative uptake of 99mTc-DMSA on pediatric patients

Introduction: Although relative uptake values aren’t the most important objective of a 99mTc-DMSA scan, they are important quantitative information. In most of the dynamic renal scintigraphies attenuation correction is essential if one wants to obtain a reliable result of the quantification process. Although in DMSA scans the absent of significant background and the lesser attenuation in pediatric patients, makes that this attenuation correction techniques are actually not applied. The geometric mean is the most common method, but that includes the acquisition of an anterior (extra) projection, which it is not acquired by a large number of NM departments. This method and the attenuation factors proposed by Tonnesen will be correlated with the absence of attenuation correction procedures. Material and Methods: Images from 20 individuals (aged 3 years +/- 2) were used and the two attenuation correction methods applied. The mean time of acquisition (time post DMSA administration) was 3.5 hours +/- 0.8h. Results: The absence of attenuation correction showed a good correlation with both attenuation methods (r=0.73 +/- 0.11) and the mean difference verified on the uptake values between the different methods were 4 +/- 3. The correlation was higher when the age was lower. The attenuation correction methods correlation was higher between them two than with the “no attenuation correction” method (r=0.82 +/- 0.8), and the mean differences of the uptake values were 2 +/- 2. Conclusion: The decision of not doing any kind of attenuation correction method can be justified by the minor differences verified on the relative kidney uptake values. Nevertheless, if it is recognized that there is a need for an accurate value of the relative kidney uptake, then an attenuation correction method should be used. Attenuation correction factors proposed by Tonnesen can be easily implemented and so become a practical and easy to implement alternative, namely when the anterior projection - needed for the geometric mean methodology – is not acquired.

Desenvolvimento de ferramentas e provetes para o ensaio Thick Adherend Shear Test (TAST).

As estruturas coladas são geralmente projetadas para que o adesivo seja essencialmente sujeito a esforços de corte, pois neste tipo de solicitação o adesivo apresenta melhores caraterísticas mecânicas. A avaliação do comportamento ao corte pode ser realizada com o adesivo no estado maciço ou como camada fina em juntas adesivas. Os métodos que permitem avaliar o comportamento ao corte, quer para o adesivo, quer para as juntas, são: o ensaio Iosipescu ou V-Notched beam shear method, o ensaio de borboleta ou Notched plate shear method (Arcan), o ensaio de torsão, o ensaio de tração numa junta de sobreposição simples e o ensaio Thick Adherend Shear Test (TAST). Os ensaios Arcan e Iosipescu, tal como o ensaio de torção, podem ser realizados em provetes de adesivo maciço ou em juntas. O ensaio de torção é pouco utilizado, porque a aplicação do esforço de corte exige dispositivos e equipamentos de ensaios complexos. Os ensaios Arcan e Iosipescu utilizam provetes com entalhes e podem introduzir alguma dificuldade na medição precisa das deformações. O ensaio de tração numa junta de sobreposição simples é um dos métodos mais usados para caraterizar uma junta adesiva, porque é um método simples, as juntas são de fácil fabrico e pode ser realizado em máquinas universais de ensaios mecânicos. Neste ensaio os aderentes estão sujeitos a uma solicitação de tração, enquanto a camada de adesivo está sujeita a esforços de corte combinados com esforços de arrancamento. Os esforços de arrancamento resultam da própria geometria da junta na qual existe um desalinhamento das forças de tração, mesmo quando são colocados calços (reguladores de espessura) nos locais de amarração. O ensaio TAST é dos mais populares para obtenção das propriedades ao corte, uma vez que tanto as ferramentas de ensaio como o fabrico dos provetes são relativamente simples. Este ensaio é realizado em junta sendo os substratos espessos e de aço que, devido à sua elevada rigidez, contribuem para um esforço de corte praticamente puro no adesivo. Neste trabalho realizou-se o projeto e a fabricação das ferramentas, gabarit e substratos necessários para a execução de provetes TAST e ensaios utilizando diferentes adesivos.

A genetic algorithm for the job shop scheduling with a new local search using Monte Carlo method

This paper presents a methodology for applying scheduling algorithms using Monte Carlo simulation. The methodology is based on a decision support system (DSS). The proposed methodology combines a genetic algorithm with a new local search using Monte Carlo Method. The methodology is applied to the job shop scheduling problem (JSSP). The JSSP is a difficult problem in combinatorial optimization for which extensive investigation has been devoted to the development of efficient algorithms. The methodology is tested on a set of standard instances taken from the literature and compared with others. The computation results validate the effectiveness of the proposed methodology. The DSS developed can be utilized in a common industrial or construction environment.

The use of the boundary element method in the analysis of single lap joints

The most common techniques for stress analysis/strength prediction of adhesive joints involve analytical or numerical methods such as the Finite Element Method (FEM). However, the Boundary Element Method (BEM) is an alternative numerical technique that has been successfully applied for the solution of a wide variety of engineering problems. This work evaluates the applicability of the boundary elem ent code BEASY as a design tool to analyze adhesive joints. The linearity of peak shear and peel stresses with the applied displacement is studied and compared between BEASY and the analytical model of Frostig et al., considering a bonded single-lap joint under tensile loading. The BEM results are also compared with FEM in terms of stress distributions. To evaluate the mesh convergence of BEASY, the influence of the mesh refinement on peak shear and peel stress distributions is assessed. Joint stress predictions are carried out numerically in BEASY and ABAQUS®, and analytically by the models of Volkersen, Goland, and Reissner and Frostig et al. The failure loads for each model are compared with experimental results. The preparation, processing, and mesh creation times are compared for all models. BEASY results presented a good agreement with the conventional methods.