Accounting Dpartment

In this paper, a single ZnO microwire-based photodetector for the monitoring of ultraviolet (UV) radiation is described. Single crystal ZnO microwires were synthesized using a chemical vapor deposition (CVD) on the Si or Al2O3 substrate. The UV photodetector was fabricated by using in-situ lift-out method in a focused ion beam system to manipulate individual zinc oxide microwire. The photodetector prototype consists of a single ZnO microwire (20 μm in length) and exhibits a response of ∼10 mA/W for UV light (365 nm) under 1 V bias. The transient response measurements revealed relatively fast response. The effect of oxygen adsorption and of different relative humidity conditions on the electronic transport through individual microwire is explored and discussed.

Using a master -slave configuration, a robust synchronization was achieved for two-color Erbium and Ytterbium mode-locked fiber lasers. Due to enhanced nonlinear interaction in the fiber, noise-free pulse-locking was achieved allowing for a cavity mismatch tolerance of 140 µ m. This is the highest tolerable cavity-length difference ever been obtained for synchronized mode-locked oscillators.

Using cross-phase modulation in an optical fiber, we synchronized the pulse train from a mode-locked ytterbium fiber laser operating at 1.05 µm to an external optical master signal. The optical master source based on a 1.54 µm distributed feedback (DFB) diode laser was driven by the clock signal and was used as a seed source. The amplified seed pulses are launched into the fiber cavity and synchronize the mode-locked pulses through cross-phase modulation. The master clock signal is electronically generated, benefiting from inherent stability and repeatability. Due to its simplicity, this technique provides an attractive alternative to the traditional scheme that uses an independent mode-locked laser as source of seed signal. Since the approach is flexible and generally applicable, we expect this stabilization method to have a good potential for use in metrology and optical communications.

This paper describes the latest research work developed at the Hydrographic Institute of the Portuguese Navy for the implementation of high-resolution numerical models able to achieve a better estimation and prediction of the wave climate in the nearshore of Portugal. As a reference was chosen a phase averaging spectral model (SWAN), which was designated by the most wave prediction programs as the community model. The experiments were performed in two different sites, one is the Pinheiro da Cruz beach, south of Lisbon in the coastal environment of Portugal continental and the other in the southern side of the Porto Santo island, archipelago of Madeira. Using the Matlab environment an original interactive computational tool with functions both for pre and post processing was developed. Besides a better visualisation and analysis, both for the input and the output, the main advantage introduced by this procedure is a significant decreasing of the computational time of the model. In this way, any location can be considered in the phase of post-processing without being imposed 'a priori' as an output request. A special attention was paid to the surf-zone processes and the associated phenomena and infragravity motions, because of the increasing interest of the Portuguese Navy in extrapolating the results delivered by the high-resolution models as an environmental support in military landing operations. In this connection the developed interface is able to provide most of the relevant parameters in the surf-zone as the location and the main characteristics of the breaking line, the type of wave breaking and the number of the wave fronts in the surf.

In this study, nanocolumnar zinc oxide thin films were catalyst-free electrodeposited directly on n-Si and p-Si substrates, what makes an important junction for optoelectronic devices. We demonstrate that ZnO thin films can be grown on Si at low cathodic potential by electrochemical synthesis. The scanning electron microscopy SEM showed that the ZnO thin films consist of nanocolumns with radius of about 150 nm on n-Si and 200 nm on p-Si substrates, possess uniform size distribution and fully covers surfaces. X-ray diffraction (XRD) measurements show that the films are crystalline material and are preferably grown along (0 0 2) direction. The impact of thermal annealing in the temperature range of 150-800°C on ZnO film properties has been carried out. Low-temperature photoluminescence (PL) spectra of the as-prepared ZnO/Si samples show the extremely high intensity of the near bandgap luminescence along with the absence of visible emission. The optical quality of ZnO thin films was improved after postdeposition thermal treatment at 150°C and 400°C in our experiments, however, the luminescence intensity was found to decrease at higher annealing temperatures (800°C). The obtained results indicate that electrodeposition is an efficient low-temperature technique for the growth of high-quality and crystallographically oriented ZnO thin films on n-Si and p-Si substrates for device applications.

Glass fiber reinforced polymers (GFRP) have become a preferable material for reinforcing or strengthening reinforced concrete structures due to their corrosion resistance, high strength to weight ratio, and relatively low cost compared with carbon fiber reinforced polymers (CFRP). However, the limited fatigue life of GFRP hinders their use in infrastructure applications. For instance, the low fatigue life of GFRP caused design codes to impose stringent stress limits on GFRP that rendered their use non-economic under significant cyclic loads in bridges. In this paper, we demonstrate that the fatigue life of GFRP can be significantly improved by an order of magnitude by incorporating Multi-Wall Carbon Nanotubes (MWCNTs) during GFRP fabrication. GFRP coupons were fabricated and tested under static tension and cyclic tension with mean fatigue stress equal to 40% of the GFRP tensile strength. Microstructural investigations using scanning electron microscopy (SEM) and Fourier Transform Infrared (FTIR) spectroscopy were used for further investigation of the effect of MWCNTs on the GFRP composite. The experimental results show the 0.5 wt% and the 1.0 wt% MWCNTs were able to improve the fatigue life of GFRP by 1143% and 986%, respectively, compared with neat GFRP.