Tuning from blue to magenta the up-converted emissions of YF3:Tm3+/Yb3+ nanocrystals

Monodisperse YF3:Tm3+/Yb3+ nanocrystals have been synthesized to explore the visible up-converting properties under near infrared (975 nm) excitation. It has been found that the nanoparticles exhibit intense red up-converted emissions, in addition to the characteristic UV and blue Tm3+-bands. It is demonstrated that, by carefully selecting Tm3+ and Yb3+ contents, the relative intensity of the different emissions can be changed producing an overall emission colour that can be tuned from blue to magenta.     

Laser shock processing influence on constitutive behaviour of graded structures produced by laser welding of ferritic to austenitic stainless steel

The main objective of the present investigation was to assess the constitutive behaviour of the graded structures produced by laser shock processing (LSP) on laser welded joints made between thin sheets of ferritic and austenitic stainless steel. First, the evolution of surface strain patterns during uniaxial loading of the as welded and LSP treated joints was experimentally obtained by using a video-image correlation technique. Overall and local constitutive behaviour across the weld, heat affected zone and parent metals resulted by coupling the applied load level with the corresponding strain average of each zone. The differences found in mechanical resistance of the LSP treated zones when comparing with the as welded ones were due to the processing features, namely the generation of compressive stresses and the development of graded surface structures. Special attention was paid on changes occurred in the ferritic steel side of the joint, which acts as a mechanical cut-out fuse in structures working in energy related applications. Then, by extrapolating the fatigue fracture behaviour of macroscopic notches to the surface cavities and irregularities from which surface topography results it was found that LSP improves the ferritic steel side fatigue resistance. Additionally, the growth of eventual surface flaws is delayed by the compressive stress state induced by LSP, as indicated by in-depth X-ray measurements.     

Production of FAMEs from several microalgal lipidic extracts and direct transesterification of the Chlorella pyrenoidosa

In this study different methods were applied for lipids extraction from the dry biomass of Chlorella pyrenoidosa. The survey was carried under different conditions seeking comparative assessment of extraction methods. The method using chloroform:methanol (2:1 v/v) showed the highest lipid extraction followed by methanol, chloroform, ethanol, and hexane. Afterward, we also assessed the relative influence of the solvent extractor selectivity on the overall FAMEs (Fatty Acids Methyl Esters) yield. The application of the transesterification process on the several lipidic extracts was compared with direct transesterification process from dry biomass. In the extraction using chloroform:methanol system a larger amount of lipids was obtained but the conversion to FAMEs using transesterification process was the lowest from lipids. However, despite the amount of extracted lipids with methanol being smaller, its conversion to FAMEs was higher from lipids. In addition, the extraction with methanol followed by transesterification process also resulted in a higher FAMEs yield from biomass than direct transesterification process using methanol.     

Influence of machining conditions on tensile stress and ductility of a mechanically alloyed Fe–40Al intermetallic

The influence of a variety of machining conditions on the tensile behaviour of a mechanically alloyed FeAl intermetallic has been examined. Yield behaviour is hardly affected by machining conditions, and ductility is only weakly sensitive to machining speed or cutting depth. This behaviour seems to be related more with the extent of subsurface damage or work hardening than with the roughness of the machined samples.     

A SPIN-based approach for detecting vulnerabilities in C programs

An approach is presented for the detection of software vulnerabilities using the widely known SPIN model checker. Classes of vulnerabilities in C programs that can be detected using the presented approach are discussed. We present the results of experiments on detecting vulnerabilities in student-made software tools implementing array processing algorithms.     

The identification of irradiated crustaceans and evaluation of the dose by thermoluminescence: Intercomparison between two methods for extracting minerals

The thermoluminescence (TL) is one of the physical methods recommended by the European Committee for Standardization, for the identification of irradiated food from which silicate minerals can be extracted. The efficacy of the method strongly depends on the quantity and purity of the extracted minerals, and therefore on the extraction procedure. In this work we applied the TL for the identification of crustacean Nephrops norvegicus irradiated at 0.5?1.5?3.0 kGy, comparing two different procedures for extracting minerals: by means of a density gradient or with acid hydrolysis. The identification of the irradiation treatment was always achieved with both procedures, without any false positive. A dose reconstruction method was also set up and tested. A little preference should be given to the acid hydrolysis extraction procedure, that requires less quantity of food sample and reagents, as well as less time to be carried out, and gives a satisfactory reconstruction of dose.     

Use of electronic speckle pattern interferometry in the detection of fatigue failure in high strength steels

The fatigue behaviour of next generation high strength steels (σ_UTS = 950–1000 MPa) has been studied. Specifically, this study is focused on the initiation stage of fatigue microcracks. With this purpose, high cycle fatigue tests under uniaxial loading have been performed. During these tests, the deformation history of the specimen has been tracked by means of speckle interferometry. This technique allows monitoring the evolution of the displacement field and its derivatives on the specimen surface, so that it can be used as a tool for detecting microcracks in the first stages of crack initiation. The observation of the fracture surfaces provides complementary information about the localization of the initiation of failure thus, a correlation between the observations made by interferometry and the actual location of the fatigue nucleus and the evolution of the crack during its propagation can be established. Results appoint speckle interferometry as a promising technique for the detection of fatigue failures.     

Base/acid-catalyzed FAEE production from hydroxylated vegetable oils

In this study was developed a new methodology to produce fatty acid ethyl esters from castor oil. The base-catalyzed transesterification step was followed by on pot addition of sulfuric acid. That addition implicated the successful separation of FAEEs/glycerin phases due to soap breaking. The study was carried out through an experimental design where the variables studied in the first step were the molar ratio alcohol:oil and the catalyst amount in the transesterification process. As expected, the on pot addition of concentrated sulfuric acid yields FFAs that increase the acid value in the FAEEs phase. A second step esterification of these free fatty acids from FAEE raw mixture was investigated. The esterification of FFA was carried out in 60:1 and 80:1 M ratios (alcohol:free fatty acids) and concentrated sulfuric acid 5% and 10% w/w (based on free fatty acids). Consequently, these two steps yielded more fatty ethyl esters and assure that the following important requirements in the FAEEs production process from castor oil are satisfied: complete reaction, best separation of FAEEs/glycerin phases, removal of catalyst, limpid glycerin, and absence of free fatty acids.     

Uncertainty Estimation for Performance Evaluation of a Confocal Microscope as Metrology Equipment

Both in industry and research, the quality control of micrometric manufactured parts is based on the measurement of parameters whose traceability is sometimes difficult to guarantee. In some of these parts, the confocal microscopy shows great aptitudes to characterize a measurand qualitatively and quantitatively. The confocal microscopy allows the acquisition of 2D and 3D images that are easily manipulated. Nowadays, this equipment is manufactured by many different brands, each of them claiming a resolution probably not in accord to their real performance. The Laser Center (Technical University of Madrid) has a confocal microscope to verify the dimensions of the micro mechanizing in their own research projects. The present study pretends to confirm that the magnitudes obtained are true and reliable. To achieve this, a methodology for confocal microscope calibration is proposed, as well as an experimental phase for dimensionally valuing the equipment by 4 different standard positions, with its seven magnifications and the six objective lenses that the equipment currently has, in the x–y and z axis. From the results the uncertainty will be estimated along with an effect analysis of the different magnifications in each of the objective lenses.