Enhanced Photorefractivity of Poly(N‐vinylcarbazole)‐Based Composites through Electric‐Field Treatments and Ionic Liquid Doping

It is shown that the photorefractive (PR) performance of polymer composites based on poly(N‐vinylcarbazole) can be improved when samples are subjected to an electric field for a certain time, i.e. conditioned, previous to the PR characterization. It is also found that for conditioned samples the addition of an organic ionic liquid to the PR composition allows to obtain PR effect without the need of using a sensitizer. The typical electric field treatment time at room temperature and at a field of 20 V µm^?1 is 20 min. This procedure leads to a decrease of dark conductivity and an increase of photoconductivity, and consequently an increase of conductivity contrast. This results in higher PR two‐beam‐coupling gain coefficients and shorter response times, particularly at low fields. Dependencies of the process dynamics on impurities, applied field strength, temperature and the presence of an organic ionic liquid are examined in detail. It is remarkable the significant increase of the PR gain coefficients, and more drastically of the net gain coefficients, observed at low fields (<55 V µm^?1), when an ionic organic liquid such as benzalkonium chloride is added to unsensitized conditioned PR composites. These findings open a new route to improve the PR performance, not only of PVK‐based composites, but also of other types of organic materials, the main advantage being that no sensitizer is needed.     

Hybrids of gold nanoparticles and oligo(p-phenyleneethynylene)s end-functionalized with alkynylruthenium groups: Outstanding two-photon absorption in the second biological window

Oligo(p-phenyleneethynylene)s (OPEs) end-capped with (alkynyl)bis(diphosphine)ruthenium and thiol/thiolate groups stabilize ca. 2 nm diameter gold nanoparticles (AuNPs). The morphology, elemental composition and stability of the resultant organometallic OPE/AuNP hybrid materials have been defined using a combination of molecular- and nano-material chacterization techniques. The hybrids display long-term stability in solution (more than a month), good solubility in organic solvents, reversible ruthenium-centered oxidation, and transparency beyond 800 nm, and possess very strong nonlinear absorption activity at the first biological window, and unprecedented two-photon absorption activity in the second biological window (σ₂ up to 38,000 GM at 1,050 nm).

     

Line-focusing holographic mirrors for solar ultraviolet energy concentration

We report on the design and the construction of a 1.3-m(2) UV selective solar concentrator intended for photocatalytic water detoxification processes. This concentrator was made by assembling 30 cm x 30 cm line-focusing holographic mirrors. Holograms with an 80% diffraction efficiency concentrate ~40% of the incident solar energy, which is effective for exciting an aqueous suspension of the TiO(2) photocatalyst, and transmit unnecessary longwave radiation. Major problems, such as the low sensitivity of the dichromated gelatin used for recording the holograms and wavelength dispersion, are discussed.     

Effects of Sintering on the Thermal and Optical Properties of Zinc Oxide Ceramic

Microstructure and composition are factors determining heat transfer in ZnO ceramic materials, which define the performance of the material after Joule heating, generated by electron transport. In this study, photothermal radiometry was applied to investigate the influence of the sintering temperature, ranging from \(800\,{^{\circ }}\hbox {C}\) to \(1300\,{^{\circ }}\hbox {C}\), by measuring the thermal diffusivity and thermal conductivity at room temperature, of commercial and sol–gel ZnO pellets. Our results show that the values of these thermal properties for both types of ZnO increase when the sintering temperature increases, displaying maximum energy dissipation at \(1200\,{^{\circ }}\hbox {C}\). Additionally, the role of the sintering temperature on the optical properties was also analyzed using diffuse reflectance spectroscopy, and from these data the optical band-gap was obtained.     

Pre-service teachers’ skills and perceptions about the use of virtual learning environments to improve teaching and learning

This paper explores data retrieved from Educational Immersive Virtual Worlds to describe pre-service teachers’ skills and perceptions about the simulation tasks. This project had 10 participants who were immersed for 3 years in the Technology and Pedagogical Models in Immersive Worlds island, a multi-user virtual environment in Second Life and Open Simulator. In this project, we evaluated how three-dimensional virtual environments can facilitate the achievement of teaching and learning processes. Based on quantitative and qualitative methodologies, two data collection instruments were applied. Through observation grids and personal log books, professional performance of the 18 pedagogical challenges implemented was collected. The statistical analysis shows that the students improved their technology skills and educational aspects about good practices in classes, regardless of the type of platform used. The analysis through Constant Comparing Method reported a positive assessment of the use of virtual environments, especially about the use of teaching strategies. Main conclusions regarding the pedagogical context reflect the importance of peer assessment on teaching performance, as well as the complexity of role-plays as intellectual challenges to enhance pre-service teachers’ skills. The main difficulties identified during the development of the activities were technical in nature, reporting hardware and connectivity issues.     

Iodine content of cattle milk from mountain and coast from Perú

With the objective to establish the cause-effect relationship between a geological area and the iodine content in cattle milk, and to estimate the contribution of milk consumption to the dietary iodine intake, the iodine content in cattle milk from the sierra and the coastal regions of Perú was determined. Milk samples were collected of cows from the three main productive zones of Perú, 62 in Cajamarca, 42 in Arequipa, both in the sierra, and 27 in Lima at the coast. The measurement of iodine was made by the method of Zak, based on the Sandell- Kolthoff reaction. The median values obtained were 24 microg/L in Cajamarca, 34 microg/L in Arequipa, and 170 microg/L in Lima. The median value in the sierra, 26 microg/L, was significantly lower than the one found in the coast. Moreover, while in the former 81% of individual values were below 50 microg/L, in the latter, on the contrary, 77% were above 80 microg/L. These results confirm that the iodine content in cattle milk is related to ecological factors. At the same time, they demonstrate that the iodine content in milk from the sierra is six times lower than in milk from the coast, and also that its consumption does not contribute significantly to satisfy the human physiological requirements of iodine in that zone.     

A plastic miniature x-ray emission spectrometer based on the cylindrical von Hamos geometry

We present a short working distance miniature x-ray emission spectrometer (miniXES) based on the cylindrical von Hamos geometry. We describe the general design principles for the spectrometer and detail a specific implementation that covers Kβ and valence level emission from Fe. Large spatial and angular access to the sample region provides compatibility with environmental chambers, microprobe, and pump/probe measurements. The primary spectrometer structure and optic is plastic, printed using a 3-dimensional rapid-prototype machine. The spectrometer is inexpensive to construct and is portable; it can be quickly set up at any focused beamline with a tunable narrow bandwidth monochromator. The sample clearance is over 27 mm, providing compatibility with a variety of environment chambers. An overview is also given of the calibration and data processing procedures, which are implemented by a multiplatform user-friendly software package. Finally, representative measurements are presented. Background levels are below the level of the Kβ(2, 5) valence emission, the weakest diagram line in the system, and photometric analysis of count rates finds that the instrument is performing at the theoretical limit.     

Modelling of the growth-no growth interface of Issatchenkia occidentalis, an olive spoiling yeast, as a function of the culture media, NaCl, citric and sorbic acid concentrations: study of its inactivation in the no growth region

A global logistic model incorporating a dummy variable for the growth medium (laboratory media or table olives brine) was used for the estimation of the growth-no growth interface of Issatchenkia occidentalis as a function of NaCl, citric and sorbic acid concentrations. The model permitted the deduction of the region where the combination of citric and sorbic acids in laboratory media (above 0.3% and 0.03% wt/vol, respectively) and brine (above 0.1% and 0.03% wt/vol), at 5% NaCl, inhibited the growth of the yeast. Subsequently, the model was validated in laboratory media within the no growth region by a response surface D-optimal design. Inactivation concentrations of sorbic acid produced a progressive loss of viability in I. occidentalis that followed a first order kinetic or downward concave inactivation curves, depending on environmental variables. These curves were properly described by a (primary) model deduced from the Weibull distribution, whose parameters, first decimal reduction time (D(beta)) and shape (beta), were expressed as a function of sorbic acid concentrations (secondary model). At 5% NaCl and within the experimental region checked, an increase of 0.010% and 0.008% sorbic acid reduced D(beta) in 10 h and decrease beta by 10%. Finally, the model was also validated in real "seasoned" table olives packing reporting a complete inactivation of the yeasts' population.