Near‐Field Lithography by Two‐Photon Induced Photocleavage of Organic Monolayers

We prove that the enhanced electromagnetic near‐field around metallic nanostructures can be used for localized two‐photon induced activation of surfaces, obtaining a defined chemical pattern with nanometric resolution. Gold nanoparticles (Au‐NP) are deposited on glass slides that were modified with a polysiloxane layer containing a nitroveratrylcarbonyl (NVoc) photoremovable group. Upon illumination with a femtosecond laser, the NVoc entity is removed. Due to the electromagnetic field enhancement of the nanoparticles, the threshold of this process is lowered in the nm‐scale vicinity of the metal structures. Upon cleavage, an amine functional group is released, which can be used to site‐selectively bind species with complementary chemical functionality on the surface. This method can be utilized for sub‐wavelength chemical structuring.     

Treatment of pollutants in wastewater: Adsorption of methylene blue onto olive-based activated carbon

This study used olive stone-based activated carbon for the removal of methylene blue from wastewater in order to evaluate the adsorption capacity of the carbon. The equilibrium and kinetics of adsorption were examined at 25°, 30°, 35° and 40 °C and several agitation speeds. Type III adsorption isotherms corresponding to physical adsorption in a multilayer system were used for the methylene blue system. The equilibrium data for methylene blue adsorption showed a good fit to the Freundlich equation. The kinetic data was analysed to determine kinetic constants and order of reaction. Kinetics was evaluated by means of an n-order model, showing that the reaction was a first-order reaction. The results indicated that olive stone-based activated carbon could be used as a low-cost alternative to commercial activated carbon for the removal of organic compounds from wastewater. However, due to its microporosity, the application of this type of activated carbon was found to be suitable for molecules smaller than methylene blue.     

DNA-mediated silver nanoclusters: synthesis, properties and applications

Fluorescent DNA-AgNCs have emerged as an alternative to standard emitters because of their unique properties: high fluorescent quantum yield, photostability, a broad pallet of colors (blue to near-IR), and the fact that their properties are easily modulated by the DNA sequence and environment. Applications as gene, ion, or small-molecule sensors have been reported.     

Bio-functionalization of ligand-free upconverting lanthanide doped nanoparticles for bio-imaging and cell targeting

We report on the functionalization of ligand-free NaGdF(4):Er(3+), Yb(3+) upconverting nanoparticles with heparin and basic fibroblast growth factor (bFGF). These upconverting nanoparticles are used to obtain high-contrast images of HeLa cells. These images reveal that the heparin-bFGF functionalized nanoparticles show specific binding to the cell membrane.     

Development of a dual-isotope procedure for the tagging and identification of manufactured products: application to explosives

A novel chemical tagging approach, based on a dual-isotope procedure, is presented. The method has been applied to explosives tagging. The method is based on the addition to the explosive of two enriched isotopes of the same element, which may be already present within it, at a given molar ratio. This dual-isotope approach will give a unique fingerprint to the tagged explosive. Further, the authentication of the tagged explosive or its residues will be obtained by comparison of the ratio of molar fractions experimentally measured by inductively coupled plasma mass spectrometry (ICP-MS) with the molar fraction ratio of the tagging mixture. The novelty of this tagging method relies on working with isotope abundances and molar fraction ratios instead of the classical isotope ratios, and this fact constitutes the strong point of the described approach since the molar ratio is not affected by physical, chemical, or biochemical processes, and it is also not disturbed by environmental contamination with the natural abundance element. Furthermore, the use of molar fraction ratios overcomes the nonhomogeneous distribution of the tagging element within the explosive. As the tagging element can be present at trace or ultratrace levels, a very small amount of enriched isotopes needs to be added, denoting a low cost solution. Also, the use of enriched stable isotopes of nontoxic elements will have negligible health effects or affect the environment.     

Transmission properties in waveguides: an optical streamline analysis

We present a novel approach to study transmission through waveguides in terms of optical streamlines. This theoretical framework combines the computational performance of beam propagation methods with the possibility to monitor the passage of light through the guiding medium by means of these sampler paths. In this way, not only can the optical flow along the waveguide be followed in detail, but also a fair estimate of the transmitted light (intensity) can be accounted for by counting streamline arrivals with starting points statistically distributed according to the input pulse. Furthermore, this approach allows elucidation of the mechanism leading to energy losses, namely, a vortical dynamics, which can be advantageously exploited in optimal waveguide design.     

Dynamic coding of temporal luminance variation

The range of variation in environmental stimuli is much larger than the visual system can represent. It is therefore sensible for the system to adjust its responses to the momentary input statistics of the environment, such as when our pupils contract to limit the light entering the eye. Previous evidence indicates that the visual system increasingly centers responses on the mean of the visual input and scales responses to its variation during adaptation. To what degree does adaptation to a stimulus varying in luminance over time result in such adjustment of responses? The first two experiments were designed to test whether sensitivity to changes in the amplitude and the mean of a 9.6° central patch varying sinusoidally in luminance at 0.6 Hz would increase or decrease with adaptation. This was also tested for a dynamic peripheral stimulus (random patches rotating on the screen) to test to what extent the effects uncovered in the first two experiments reflect retinotopic mechanisms. Sensitivity to changes in mean and amplitude of the temporal luminance variation increased sharply the longer the adaptation to the variation, both for the large patch and the peripheral patches. Adaptation to luminance variation leads to increased sensitivity to temporal luminance variation for both central and peripheral presentation, the latter result ruling retinotopic mechanisms out as sole explanations for the adaptation effects.     

Inductive method for assessing the amount and orientation of steel fibers in concrete

Steel fibers are ferromagnetic and they have the property of altering the magnetic field around them. This paper discusses a method and gives a practical example to measure, non-destructively, the amount and orientation of fibers from cubic concrete specimens (150?mm). This is possible because the fibers affect inductance of a sensor (an inductive coil) that is wrapped around the specimen.     

Wireless sensor node localization

For most wireless sensor network (WSN) applications, the positions of the sensor nodes need to be known. Global positioning systems have not fitted into WSNs very well owing to their price, power consumption, accuracy and limitations in their operating environment. Hence, the last decade has brought about a large number of proposed methods for WSN node localization. They show tremendous variation in the physical phenomena they use, the signal properties they measure, the resources they consume, as well as in their accuracy, range, advantages and limitations. This paper provides a high-level, comprehensive overview of this very active research area.     

Analysis of laser scanning and strategies for dimensional and geometrical control

Noncontact scanning systems are becoming more present in the industry every day. These systems allow a significant reduction in manufacturing costs, mainly due to the important decrement in the inspection time. They enable obtaining a great amount of data that provides very good levels of quality in results. In spite of the well-known advantages that these systems offer, there are also some difficulties, such as the undefined and nonstandardized accuracy when compared with traditional inspection systems based on touch-trigger probes. That is one of the reasons for the practical absence of scanning systems in metrological applications: they have not been adequately tested in terms of accuracy for geometric and dimensional tolerance control. In fact, these systems are mainly used in reverse engineering or multimedia applications. The goal pursued in this research is to analyze the applicability of scanning systems for measuring and control of tolerances. Two different scanning systems were analyzed: a laser triangulation sensor and a touch-trigger probe, both mounted on a coordinate measuring machine. Several test parts were designed, which include different canonical features: planes, spheres, cylinders, holes (outer and inner), and conical surfaces. A common alignment method was defined in order to compare the geometry generated for both scanning systems. Different scanning orientation strategies were defined for laser scanning. Besides this, features were reconstructed with several computer-aided design systems, and the correlation between the contact and noncontact geometries was analyzed to study the convergence of results among them. Finally, an analysis was carried out to compare them in terms of geometrical and dimensional tolerances, considering the contact measurements as datum. As a result, some advises are given with respect to the best strategies for scanning, estimating the deviations.