Surface photochemistry: benzophenone as a probe for the study of silica and reversed-phase silica surfaces

This work reports the use of benzophenone, a very well characterized probe, to study new hosts: two reversed-phase silicas. Laser-induced room temperature luminescence of argon purged solid powdered samples of benzophenone adsorbed onto the two different reversed-phase silicas, RP-18 and RP-8, revealed the existence of a low energy emission band in contrast with the benzophenone adsorbed on 60 A pore silica, where only triplet benzophenone emits. This low energy emission band was identified as the fluorescence of the ketyl radical of benzophenone, which is formed as the result of a hydrogen atom abstraction reaction of the triplet excited benzophenone from the alkyl groups of the surface of the reversed silicas. Such emission does not exist for benzophenone adsorbed onto 60 A pore silica. Room temperature phosphorescence was obtained in argon purged samples for all the surfaces under use. The decay times of the benzophenone emission vary greatly with the alkylation of the silica surface when compared with "normal" silica surface. A lifetime distributions analysis has shown that the shortest lifetimes for the benzophenone emission exist in the former case. Triplet-triplet absorption of benzophenone was detected in all cases and is the predominant absorption in the case of 60 A pore silica, while benzophenone ketyl radical formation occurs in the case of the reversed silicas. Diffuse reflectance laser. ash photolysis and gas chromatography-mass spectrometry techniques provided complementary information, the former about transient species and the latter regarding the final products formed after laser irradiation, both at 266 nm or 355 nm. Product analysis and identification show that the degradation photoproducts are dependent on the excitation wavelength, the photochemistry being much more rich and complex in the 266 nm excitation case, where an alpha-cleavage reaction occurs. A detailed mechanistic analysis is proposed

Efficiency of different techniques in flexural strengthening of RC beams under monotonic and fatigue loading

In the context of flexural strengthening of concrete structures, fiber reinforced polymers (FRP) have been used mostly by two main techniques: Externally Bonded Reinforcement (EBR) and Near-Surface Mounted (NSM). Both strengthening techniques are applied on the cover concrete, which is normally the weakest region of the element to be strengthened. Consequently, the most common problem is the premature failure of the strengthening system that occurs more frequently in the EBR one. In an attempt of overcoming this weakness, another technique has been proposed, called MF-EBR – Mechanically Fastened and Externally Bonded Reinforcement, which uses multi-directional carbon fiber laminates, simultaneously glued and anchored to concrete. To compare the efficiency of NSM, EBR and MF-EBR techniques, four-point bending tests with RC beams were carried out under monotonic and cyclic loading. In this work the tests are described in detail and the obtained results are discussed. Additionally, to assess the performance of a FEM-based computer program for the prediction of the behaviour of RC beams strengthening according to these techniques, the beams submitted to monotonic loading were numerically simulated.FCT; Hilti Portugal - Productos e Serviços Lda.; S&P Clever Reinforcement Ibérica Lda.; SECIL; TSwaterjet, Lda

Experimental and numerical study of distinct techniques to strengthen beams failing in bending under monotonic loading

With the purpose of study three distinct techniques to strengthen beams failing in bending under monotonic loading, an experimental program was carried out. Three techniques are analyzed: Externally Bonded Reinforcement (EBR), Near-Surface Mounted (NSM) and Mechanically Fastened and Externally Bonded Reinforcement (MF-EBR). Unidirectional CFRP laminates were used for the case of the EBR and NSM techniques, whereas multi-directional CFRP laminates were used with the MF-EBR system. In this work the tests are described in detail, and the obtained results are presented and discussed. Numerical simulations of the tests are presented to evaluate the ability of current FEM tools in the simulation of these strengthening techniques

Efficiency of different FRP-based flexural strengthening techniques in beams submitted to fatigue loading

Flexural strengthening of reinforced concrete (RC) structures with fiber reinforced polymers (FRP) has been used mostly by two main techniques: Externally Bonded Reinforcement (EBR) and Near-Surface Mounted (NSM). In both strengthening techniques the FRP systems are applied on the cover concrete, which is normally the weakest region of the element to be strengthened. Consequently, the most common problem is the premature failure of the system, which occurs more frequently when using the EBR technique. In an attempt of overcoming this weakness, another flexural strengthening technique, named MF-EBR – Mechanically Fastened and Externally Bonded Reinforcement, is analyzed in the present paper. This technique uses multidirectional carbon fiber laminates that are simultaneously glued and anchored to concrete. To compare the efficiency of NSM, EBR and MF-EBR techniques, four-point bending tests with RC beams were carried out under monotonic and fatigue loading. In this work the tests are described and the obtained results are presented and discussed.Fundação para a Ciência e a Tecnologia (FCT) - PTDC/ECM/74337/200

Eficiência de diferentes técnicas de reforço à flexão de vigas de betão armado

A utilização de polímeros reforçados com fibras (FRP) no contexto do reforço de estruturas de Engenharia Civil tem crescido nas últimas décadas. Propriedades como baixo peso, elevado rácio rigidez/peso, imunidade e à corrosão e grande variedade de tamanhos e formatos disponíveis são algumas das razões que justificam a crescente utilização deste tipo de materiais. A sua aplicação tem sido realizada a essencialmente através de duas técnicas de reforço: colagem externa (Externally Bonded Reinforcement – EBR) e inserção no betão de recobrimento (Near-Surface Mounted – NSM). A eficiência dessas técnicas depende, principalmente do desempenho da ligação. Dado que este e tipo de reforço é aplicado ao nível do betão de recobrimento, que e é normalmente a região com as pioores propriedades mecânicas do elemento a ser reforçado, é frequente a ocorrência de e rotura precoce do reforço pelo seu destacamento. Na tentativa de solucionar esse problema, outras técnicas têm sido propostas. A técnica que a aqui se apresenta utiliza laminados multi-direccionais de fibra de carbono simultaneamente colados e ancorados ao betão, tendo sido designada por técnica MF-EBR – Mechanically Fastened and Externally Bonded Reinforcement. Com vista à comparação da eficiência da técnica proposta com as técnicas s EBR e NSM procedeu-se à realização de um programa de ensaios experimentais com vigas de betão armado. Assim, no presente trabalho os ensaios realizados são descritos e os resultados mais significativos são apresentados e analisados

Pyrene-p-tert-butylcalixarenes inclusion complexes formation: a surface photochemistry study

Diffuse reflectance and luminescence techniques were used to study the photophysics and photochemistry of pyrene within p-tert-butylcalix[n]arenes with n = 4, 6, and 8, and to study their ability to form inclusion complexes in heterogeneous media. Evidences for inclusion complex formation were found for the three hosts under study. Ground state diffuse reflectance results have shown the formation of ground state dimers of pyrene inside the cavity of calix[ 6] arene and calix[ 8] arene, with this feature much more evident for calix[ 6] arene. For calix[ 4] arene, only a monomer fits inside the cavity and the presence of pyrene microcrystals outside the cavity was detected. A luminescence lifetime distribution analysis was performed, revealing the presence of prompt emissions from the pyrene microcrystals outside the cavity in the case of calix[ 4] arene and from the constrained dimers inside the cavities of calix[ 6] arene and calix[ 8] arene. Transient absorption results have shown the presence of pyrene radical cation and also of trapped electrons for the three hosts under study. The formation of the phenoxyl radical of the calixarene following the laser pulsed excitation of pyrene at 355 nm is increased for calix[ 6] arene and calix[ 8] arene. This feature is particularly relevant for calix[ 6] arene, suggesting a very favourable situation for the hydrogen atom abstraction to occur. The analysis of the degradation products revealed the presence of hydroxypyrene as a major photodegradation product for the three hosts. Dihydro-hydroxypyrene was also formed in the case of calix[ 6] arene and calix[ 8] arene. The formation of the calixarene's phenoxyl radical and subsequent hydrogen abstraction is consistent with the formation of dihydro-dihydroxypyrene

The AIVA fly-by-wireless UAV platform

The AIVA project concerns to an UAV aimed to perform aerial surveillance, forest fire detection and also to monitor high voltage cables for stress or failures. The global project involves the design and development of the required aerial platform, as well as the electronics, communications hardware and software, flight control, artificial vision and systems integration, in order to provide an autonomous takeoff, flight mission and landing manoeuvres. Relevant goals, regarding the design and development of the AIVA platform, initiated in September 2004, have already been achieved, and they will be described over next topics. [...

A bluetooth-based wireless distributed data acquisition and control system

This paper presents an application independent embedded platform for a wireless distributed data acquisition and control system, and describes its application in the scenario of controlling the information processing and communications between sensors and actuators onboard of an autonomous flying robot, in a “fly-by-wireless” approach. The system, which was designed and implemented, comprises a set of nodes composed by microcontrollers, wireless communication modules based on Bluetooth technology, and sensing/actuation devices. This paper also presents several experimental results which denote encouraging performance characteristics for the developed system, not only in the context of the proposed application, but for other wireless applications as well

Distributed sensing and actuation over bluetooth for unmanned air vehicles

A short range wireless network platform, based on Bluetooth technology and on a Round Robin scheduling is presented. The objective is to build an application independent platform, to support a distributed sensing and actuation control system, which will be used in an Unmanned Aerial Vehicle (UAV). This platform provides the advantages of wireless communications while assuring low weight, small energy consumption and reliable communications

A fly-by-wireless UAV platform based on a flexible and distributed system architecture

This paper reports and describes the diverse stages concerning the development of an unmanned aerial vehicle (UAV) named “Aeronave Inteligente com Visão Artificial”, better known by its acronym as AIVA. The design and development of the first aerial platform, the onboard ommunications, the instrumentation system, the bidirectional communications platform to/from ground station, the flight control system, the navigation strategies, as well as the vision systems to help navigation and to carry out the planned surveillance missions, are addressed in this paper. One of the main innovative issues of this platform is the distributed onboard wireless network, based on Bluetooth technology and on a multiprocessor architecture system. These features increase the platform flexibility. The goals already accomplished so far reveal interesting developments to be used successfully in commercial UAV platforms