Mechanical performance of concrete made with aggregates from construction and demolition waste recycling plants

This research aims at analysing the mechanical performance of concrete with recycled aggregates (RA) from construction and demolition waste (CDW) from various locations in Portugal. First the characteristics of the various aggregates (natural and recycled) used in the production of concrete were thoroughly analysed. The composition of the RA was determined and several physical and chemical tests of the aggregates were performed. In order to evaluate the mechanical performance of concrete, compressive strength (in cubes and cylinders), splitting tensile strength, modulus of elasticity and abrasion resistance tests were performed. Concrete mixes with RA from CDW from several recycling plants were evaluated, in order to understand the influence that the RA's collection point, and consequently their composition, has on the characteristics of the mixes produced. The analysis of the mechanical performance allowed concluding that the use of RA worsens most of the properties tested, especially when fine RA are used. On the other hand, there was an increase in abrasion resistance when coarse RA were used. In global terms, the use of this type of aggregates, in limited contents, is viable from a mechanical viewpoint. (C) 2015 Elsevier Ltd. All rights reserved.

Mechanical and thermal characterization of a structural polyurethane adhesive modified with thermally expandable particles

Thermally expandable particles (TEPs) are used in a wide variety of applications by industry mainly for weight reduction and appearance improvement for thermoplastics, inks, and coatings. In adhesive bonding, TEPs have been used for recycling purposes. However, TEPs might be used to modify structural adhesives for other new purposes, such as: to increase the joint strength by creating an adhesive functionally modified along the overlap of the joint by gradual heating and/or to heal the adhesive in case of damage. In this study, the behaviour of a structural polyurethane adhesive modified with TEPs was investigated as a preliminary study for further investigations on the potential of TEPs in adhesive joints. Tensile bulk tests were performed to get the tensile properties of the unmodified and TEPs-modified adhesive, while Double Cantilever Beam (DCB) test was performed in order to evaluate the resistance to mode I crack propagation of unmodified and TEPs-modified adhesive. In addition, in order to investigate the behaviour of the particles while encapsulated in adhesives, a thermal analysis was done. Scanning electron microscopy (SEM) was used to examine the fracture surface morphology of the specimens. The fracture toughness of the TEPs-modified adhesive was found to increase by addition of TEPs, while the adhesive tensile strength at yield decreased. The temperature where the particles show the maximum expansion varied with TEPs concentration, decreasing with increasing the TEPs content.

A physical packing sequence algorithm for the container loading problem with static mechanical equilibrium conditions

The container loading problem (CLP) is a combinatorial optimization problem for the spatial arrangement of cargo inside containers so as to maximize the usage of space. The algorithms for this problem are of limited practical applicability if real-world constraints are not considered, one of the most important of which is deemed to be stability. This paper addresses static stability, as opposed to dynamic stability, looking at the stability of the cargo during container loading. This paper proposes two algorithms. The first is a static stability algorithm based on static mechanical equilibrium conditions that can be used as a stability evaluation function embedded in CLP algorithms (e.g. constructive heuristics, metaheuristics). The second proposed algorithm is a physical packing sequence algorithm that, given a container loading arrangement, generates the actual sequence by which each box is placed inside the container, considering static stability and loading operation efficiency constraints.

Assessing Reading Abilities of Mechanical Engineering College Students: A Prospecting Study*

Reading is a basic competence that students have to master to be successful. Despite this fact, recent studies show that there may be a significant decline in the reading abilities of college students, one of the most educated segments of any population. This work is a prospecting study regarding the assessment of reading abilities of college students, namely in the context of Engineering education. Based on an existing screening test for assessing reading difficulties of children and teenagers, this work presents the results obtained by administrating that test to students at a top engineering institution in Portugal. An outcome of this study is the determination of a time range suitable for a massive, time limited, use of the previously mentioned test to assess college students, thus enabling a basic tool that will permit, in future works, to screen reading abilities in wider college populations. This work also shows evidence that ca. 20% of college students present a poor reading performance, revealing a strong need for monitoring college students��� reading abilities along different generations.

Reply to: Comments on ���Particle Swarm Optimization with Fractional-Order Velocity���

We agree with Ling-Yun et al. [5] and Zhang and Duan comments [2] about the typing error in equation (9) of the manuscript [8]. The correct formula was initially proposed in [6, 7]. The formula adopted in our algorithms discussed in our papers [1, 3, 4, 8] is, in fact, the following: ...

Modelling of the kinetics of municipal solid waste composting in full-scale mechanical-biological treatment plants

A thesis submitted in fulfilment of the requirements for the Degree of Doctor of Philosophy in Sanitary Engineering in the Faculty of Sciences and Technology of the New University of Lisbon

Design of New Materials for Passive Vibration Control

The aim of this contribution is to extend the techniques of composite materials design to non-linear material behaviour and apply it for design of new materials for passive vibration control. As a first step a computational tool allowing determination of macroscopic optimized one-dimensional isolator behaviour was developed. Voigt, Maxwell, standard and more complex material models can be implemented. Objective function considers minimization of the initial reaction and/or displacement peak as well as minimization of the steady-state amplitude of reaction and/or displacement. The complex stiffness approach is used to formulate the governing equations in an efficient way. Material stiffness parameters are assumed as non-linear functions of the displacement. The numerical solution is performed in the complex space. The steady-state solution in the complex space is obtained by an iterative process based on the shooting method which imposes the conditions of periodicity with respect to the known value of the period. Extension of the shooting method to the complex space is presented and verified. Non-linear behaviour of material parameters is then optimized by generic probabilistic meta-algorithm, simulated annealing. Dependence of the global optimum on several combinations of leading parameters of the simulated annealing procedure, like neighbourhood definition and annealing schedule, is also studied and analyzed. Procedure is programmed in MATLAB environment.

Determina����o das propriedades mec��nicas �� tra����o de adesivos estruturais fr��geis e d��cteis

A crescente evolu����o na tecnologia das juntas coladas conferiu um potencial atractivo ��s liga����es adesivas, com aplica����es nas mais variadas ind��strias. Isto deve-se n��o s�� aos aspetos econ��micos, tais como a melhoria da cad��ncia de produ����o mas tamb��m �� resist��ncia mec��nica que estas proporcionam. A possibilidade de ligar facilmente materiais distintos, a distribui����o mais uniforme das tens��es, a melhor resist��ncia �� fadiga e a elevada capacidade de amortecimento de vibra����es est��o entre as principais vantagens da utiliza����o deste tipo de liga����o. Estas propriedades transformam as juntas coladas numas das preferidas no momento de sele����o de meios de uni��o. O trabalho desenvolvido nesta disserta����o enquadra-se no ��mbito das liga����es adesivas e tem como principais objetivos a produ����o de uma ferramenta para a produ����o de provetes de adesivo, assim como a determina����o das propriedades mec��nicas �� tra����o dos mesmos para testar o desempenho do molde fabricado. Para tal, utilizou-se um adesivo fr��gil (Araldite�� AV 138), um d��ctil (Araldite�� 2015) e um muito d��ctil (SikaForce�� 7888). Paralelamente �� selecionado o m��todo mais adequado na obten����o destes provetes, designadamente escolhendo entre a molda����o em molde aberto e a inje����o em molde fechado. Com vista �� obten����o dos provetes, foi projetado e constru��do um molde em a��o. Recorrendo �� m��quina de tra����o Shimadzu AG ��� X 100, realizaram-se os respetivos ensaios de tra����o, para a determina����o de todas as propriedades mec��nicas dos adesivos. Para efeitos de compara����o de resultados foram utilizados dois tipos de extens��metros, um mec��nico e um ��tico. Os resultados experimentais permitiram observar que a presen��a de vazios afetou especialmente a deforma����o de rotura e a tens��o de rotura. Detetaram-se pequenas discord��ncias, comparativamente com os estudos publicados, de algumas caracter��sticas mec��nicas obtidas dos diversos adesivos utilizados. Constatou-se tamb��m um ligeiro desfasamento entre os valores adquiridos com os dois tipos de extens��metros utilizados.

Desenvolvimento de programa em linguagem Matlab�� para c��lculo pelo m��todo de elementos finitos

Para o projeto de qualquer estrutura existente (edif��cios, pontes, ve��culos, m��quinas, etc.) �� necess��rio conhecer as condi����es de carga, geometria e comportamento de todas as suas partes, assim como respeitar as normativas em vigor nos pa��ses nos quais a estrutura ser�� aplicada. A primeira parte de qualquer projeto nesta ��rea passa pela fase da an��lise estrutural, onde s��o calculadas todas as intera����es e efeitos de cargas sobre as estruturas f��sicas e os seus componentes de maneira a verificar a aptid��o da estrutura para o seu uso. Inicialmente parte-se de uma estrutura de geometria simplificada, pondo de parte os elementos f��sicos irrelevantes (elementos de fixa����o, revestimentos, etc.) de maneira a simplificar o c��lculo de estruturas complexas e, em fun����o dos resultados obtidos da an��lise estrutural, melhorar a estrutura se necess��rio. A an��lise por elementos finitos �� a ferramenta principal durante esta primeira fase do projeto. E atualmente, devido ��s exig��ncias do mercado, �� imprescind��vel o suporte computorizado de maneira a agilizar esta fase do projeto. Existe para esta finalidade uma vasta gama de programas que permitem realizar tarefas que passam pelo desenho de estruturas, an��lise est��tica de cargas, an��lise din��mica e vibra����es, visualiza����o do comportamento f��sico (deforma����es) em tempo real, que permitem a otimiza����o da estrutura em an��lise. Por��m, estes programas demostram uma certa complexidade durante a introdu����o dos par��metros, levando muitas vezes a resultados errados. Assim sendo, �� essencial para o projetista ter uma ferramenta fi��vel e simples de usar que possa ser usada para fins de projeto de estruturas e otimiza����o. Sobre esta base nasce este projeto tese onde se elaborou um programa com interface gr��fica no ambiente Matlab�� para a an��lise de estruturas por elementos finitos, com elementos do tipo Barra e Viga, quer em 2D ou 3D. Este programa permite definir a estrutura por meio de coordenadas, introdu����o de forma r��pida e clara, propriedades mec��nicas dos elementos, condi����es fronteira e cargas a aplicar. Como resultados devolve ao utilizador as rea����es, deforma����es e distribui����o de tens��es nos elementos quer em forma tabular quer em representa����o gr��fica sobre a estrutura em an��lise. Existe ainda a possibilidade de importa����o de dados e exporta����o dos resultados em ficheiros XLS e XLSX, de maneira a facilitar a gest��o de informa����o. Foram realizados diferentes testes e an��lises de estruturas de forma a validar os resultados do programa e a sua integridade. Os resultados foram todos satisfat��rios e convergem para os resultados de outros programas, publicados em livros, e para c��lculo a m��o feitos pelo autor.

A New ROV Design: Issues on Low Drag and Mechanical Symmetry

This paper reports the design of a new remotely operated underwater vehicle (ROV), which has been developed at the Underwater Systems and Technology Laboratory (USTL) - University of Porto. This design is contextualized on the KOS project (Kits for underwater operations). The main issues addressed here concern directional drag minimization, symmetry, optimized thruster positioning, stability and layout of ROV components. This design is aimed at optimizing ROV performance for a set of different operational scenarios. This is achieved through modular configurations which are optimized for each different scenario.

Incidence of respiratory viruses in preterm infants submitted to mechanical ventilation

The objectives of this study were to determine the incidence of infection by respiratory viruses in preterm infants submitted to mechanical ventilation, and to evaluate the clinical, laboratory and radiological patterns of viral infections among hospitalized infants in the neonatal intensive care unit (NICU) with any kind of acute respiratory failure. Seventy-eight preterm infants were studied from November 2000 to September 2002. The newborns were classified into two groups: with viral infection (Group I) and without viral infection (Group II). Respiratory viruses were diagnosed in 23 preterm infants (29.5%); the most frequent was respiratory syncytial virus (RSV) (14.1%), followed by influenza A virus (10.2%). Rhinorrhea, wheezing, vomiting and diarrhea, pneumonia, atelectasis, and interstitial infiltrate were significantly more frequent in newborns with nosocomial viral infection. There was a correlation between nosocomial viral infection and low values of C-reactive protein. Two patients with mixed infection from Group I died during the hospital stay. In conclusion, RSV was the most frequent virus in these patients. It was observed that, although the majority of viral lower respiratory tract infections had a favorable course, some patients presented a serious and prolonged clinical manifestation, especially when there was concomitant bacterial or fungal infection.

An evaluation of manual and mechanical methods to identify Candida spp. from human and animal sources

To compare two yeast identification methods, i. e, the manual and the VITEK mechanical methods, 62 clinical samples from hemocultures and animal sources were analyzed. After identification as Candida yeasts by the VITEK method, the strains were recharacterized using manual assimilation methods and sugar fermentation tests. Our findings reveal 58% concurrent identification between the two methods for animal strains, and 51% for human hemoculture strains.

Probabilistic models for mechanical properties of prestressing strands

This study focus on the probabilistic modelling of mechanical properties of prestressing strands based on data collected from tensile tests carried out in Laborat��rio Nacional de Engenharia Civil (LNEC), Portugal, for certification purposes, and covers a period of about 9 years of production. The strands studied were produced by six manufacturers from four countries, namely Portugal, Spain, Italy and Thailand. Variability of the most important mechanicalproperties is examined and the results are compared with the recommendations of the ProbabilisticModel Code, as well as the Eurocodes and earlier studies. The obtained results show a very low variability which, of course, benefits structural safety. Based on those results, probabilistic modelsfor the most important mechanical properties of prestressing strands are proposed.

Febrifugine derivative antimalarial activity: quantum mechanical predictors

Plasmodium falciparum resistant strain development has encouraged the search for new antimalarial drugs. Febrifugine is a natural substance with high activity against P. falciparum presenting strong emetic property and liver toxicity, which prevent it from being used as a clinical drug. The search for analogues that could have a better clinical performance is a current topic. We aim to investigate the theoretical electronic structure by means of febrifugine derivative family semi-empirical molecular orbital calculations, seeking the electronic indexes that could help the design of new efficient derivatives. The theoretical results show there is a clustering in well-defined ranges of several electronic indexes of the most selective molecules. The model proposed for achieving high selectivity was tested with success.

The effect of adhesive thickness on the mechanical behavior of a structural polyurethane adhesive

One parameter that influences the adhesively bonded joints performance is the adhesive layer thickness. Hence, its effect has to be investigated experimentally and should be taken into consideration in the design of adhesive joints. Most of the results from literature are for typical structural epoxy adhesives which are generally formulated to perform in thin sections. However, polyurethane adhesives are designed to perform in thicker sections and might have a different behavior as a function of adhesive thickness. In this study, the effect of adhesive thickness on the mechanical behavior of a structural polyurethane adhesive was investigated. The mode I fracture toughness of the adhesive was measured using double-cantilever beam (DCB) tests with various thicknesses of the adhesive layer ranging from 0.2 to 2 mm. In addition, single lap joints (SLJs) were fabricated and tested to assess the influence of adhesive thickness on the lap-shear strength of the adhesive. An increasing fracture toughness with increasing adhesive thickness was found. The lap-shear strength decreases as the adhesive layer gets thicker, but in contrast to joints with brittle adhesives the decrease trend was less pronounced.