Studies on the structure and gas sensing properties of nickel–cobalt ferrite thin films prepared by spin coating

The influence of Co²⁺ ions content on structure and sensing properties of Ni_1−xCo_xFe₂O₄ (x = 0.25, 0.5, 0.75) thin films deposited on glass substrates by spin coating is presented. Structural characterization evidenced thin films with cubic spinel structures and morphologies dependent on cobalt content. Repartition of cations in spinel tetrahedral and octahedral sites was determined and was found that the presence of Co²⁺ ions in octahedral sites favor the formation of Fe²⁺ species. The sensitivity to some reducing vapor gases (acetone, liquefied petroleum gas LPG, ethyl alcohol and methyl alcohol) was investigated and was found that thin films with x = 0.75 exhibit high sensitivity to ethyl alcohol and thin films with x = 0.25 have high sensitivity to acetone. This sensitivity largely depends on the temperature and test gas concentration and was related to the Fe²⁺ species formed in octahedral sites.     

Multi-height phase recovery combined with Fast Iterative Shrinkage-Thresholding Algorithm to handle phase microspheres from complex diffracted field in inline holography

ABSTRACT

We describe in this work an approach that individually combines constant initialization, free-space backpropagation, transport of intensity equation (TIE) and multi-height phase recovery with Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) to predict reconstruction of the phase microspheres from diffracted field measurements. We incorporate appropriate initialization and regularization to reconstruct unknown phase microspheres (transparent objects).     

Electrical Detection of Spin Precession in Freely Suspended Graphene Spin Valves on Cross‐Linked Poly(methyl methacrylate)

Spin injection and detection is achieved in freely suspended graphene using cobalt electrodes and a nonlocal spin‐valve geometry. The devices are fabricated with a single electron‐beam‐resist poly(methyl methacrylate) process that minimizes both the fabrication steps and the number of (aggressive) chemicals used, greatly reducing contamination and increasing the yield of high‐quality, mechanically stable devices. As‐grown devices can present mobilities exceeding 10⁴ cm² V^?1 s^?1 at room temperature and, because the contacts deposited on graphene are only exposed to acetone and isopropanol, the method is compatible with almost any contacting material. Spin accumulation and spin precession are studied in these nonlocal spin valves. Fitting of Hanle spin precession data in bilayer and multilayer graphene yields a spin relaxation time of ～125‐250 ps and a spin diffusion length of 1.7‐1.9 μm at room temperature.     

Superparamagnetic Unusual Behavior of Micrometric Magnetite Monodisperse Monocrystals Synthesized by Fe-EDTA Thermal Decomposition

We developed a new procedure for synthesizing micrometric magnetite by hydrothermal decomposition of the Fe-EDTA complex in the presence of urea, starting from Fe(III)-ferric ammonium sulfate and Na₄EDTA as main precursors. Microcrystals with superparamagnetic behavior with 25–45 μm in size were obtained (5 emu/g at 3.8 kOe magnetic field).     

A multi-objective adaptive immune algorithm for multi-application NoC mapping

Current SoC design trends are characterized by the integration of larger amount of IPs targeting a wide range of application fields. Such multi-application systems are constrained by a set of requirements. In such scenario network-on-chips (NoC) are becoming more important as the on-chip communication structure. Designing an optimal NoC for satisfying the requirements of each individual application requires the specification of a large set of configuration parameters leading to a wide solution space. It has been shown that IP mapping is one of the most critical parameters in NoC design, strongly influencing the SoC performance. IP mapping has been solved for single application systems using single and multi-objective optimization algorithms. In this paper we propose the use of a multi-objective adaptive immune algorithm (M²AIA), an evolutionary approach to solve the multi-application NoC mapping problem. Latency and power consumption were adopted as the target multi-objective functions. To compare the efficiency of our approach, our results are compared with those of the genetic and branch and bound multi-objective mapping algorithms. We tested 11 well-known benchmarks, including random and real applications, and combines up to 8 applications at the same SoC. The experimental results showed that the M²AIA decreases in average the power consumption and the latency 27.3 and 42.1 % compared to the branch and bound approach and 29.3 and 36.1 % over the genetic approach.     

Measuring perceptual contrast in digital images

In this paper we present a novel method to measure perceptual contrast in digital images. We start from a previous measure of contrast developed by Rizzi et al. [26], which presents a multilevel analysis. In the first part of the work the study is aimed mainly at investigating the contribution of the chromatic channels and whether a more complex neighborhood calculation can improve this previous measure of contrast. Following this, we analyze in detail the contribution of each level developing a weighted multilevel framework. Finally, we perform an investigation of Regions-of-Interest in combination with our measure of contrast. In order to evaluate the performance of our approach, we have carried out a psychophysical experiment in a controlled environment and performed extensive statistical tests. Results show an improvement in correlation between measured contrast and observers perceived contrast when the variance of the three color channels separately is used as weighting parameters for local contrast maps. Using Regions-of-Interest as weighting maps does not improve the ability of contrast measures to predict perceived contrast in digital images. This suggests that Regions-of-Interest cannot be used to improve contrast measures, as contrast is an intrinsic factor and it is judged by the global impression of the image. This indicates that further work on contrast measures should account for the global impression of the image while preserving the local information.     

Spatial pooling for measuring color printing quality attributes

Many objective image quality assessment algorithms firstly apply quality metrics in local regions that results in a quality map, and then pool the quality values in the quality map into a single quality score. The simplest pooling method is the average of quality values, which assumes that all the quality values are independent and equally important. However, visual perception is so complex that the assumption underlying average pooling might be too strict. There is an agreement that some regions in the images might be more perceptually significant, which leads to more advanced spatial pooling methods. In this work we evaluate existing spatial pooling methods for five important quality attributes, which are proposed to reduce the complexity of image quality assessment. The results show that: (1) more advanced spatial pooling methods are generally better than simple average; (2) spatial pooling depends on both image quality metrics and the attributes of the image.     

Information content of the near field: three-dimensional samples

We present an analysis of the accuracy and information content of three-dimensional reconstructions of the dielectric susceptibility of a sample from noisy, near-field holographic measurements, such as those made in scanning probe microscopy. Holographic measurements are related to the dielectric susceptibility via a linear operator within the accuracy of the first Born approximation. The maximum-likelihood reconstruction of the dielectric susceptibility is expressed as a linear combination of basis functions determined by singular value decomposition of the weighted measurement operator. Maximum a posteriori estimates based on prior information are also discussed. Semianalytical expressions are given for the likely error due to measurement noise in the basis function coefficients, resulting in effective resolution limits in all three dimensions. These results are illustrated by numerical examples.     

Photoinduced electron transfer reactions: from the elucidation of old problems in bulk solutions towards the exploration of interfaces

The activities of our research group in the field of photoinduced electron transfer reactions are discussed and illustrated by several examples.