Passivity based visual servoing of mobile robots with dynamics compensation

This paper presents an image-based dynamic visual servoing to make a mobile robot able to track a moving object on the workspace by using a calibrated on board vision system. The stability of the proposed system is proved based on its passivity properties. A robustness analysis and an L₂-gain performance analysis are also presented. Experimental results are shown to illustrate the system performance.     

Composite with Recyclable Loads for the Manufacture of Blocks to Build Popular Houses

The science space in a state school in Natal city was built using a composite consisting of gypsum, EPS （expanded polystyrene）, shredded tire, cement and water. Mechanical and thermal resistances were evaluated. Inside the blocks, three types of fillings （EPS plates, aluminum cans and 500 mL bottles of mineral water） were placed in order to obtain a walls with higher thermal resistance, but also to give it an ecologically correct order, considering that both the tire and the EPS occupy a large space in landfills and require years to be degraded when released into the environment. Compression tests were conducted according to the rules. The experiments demonstrated that the temperature difference between the internal and external surfaces on the walls reached levels above 12.0 ℃. It was also demonstrated that the proposed composite has adequate mechanical strength to be used for sealing walls. The proposed use of the composite can contribute to reduce the significant housing deficit of Brazil, producing popular houses at low cost and with little time to work.     

Verification of cardiac tissue electrophysiology simulators using an N-version benchmark

Ongoing developments in cardiac modelling have resulted, in particular, in the development of advanced and increasingly complex computational frameworks for simulating cardiac tissue electrophysiology. The goal of these simulations is often to represent the detailed physiology and pathologies of the heart using codes that exploit the computational potential of high-performance computing architectures. These developments have rapidly progressed the simulation capacity of cardiac virtual physiological human style models; however, they have also made it increasingly challenging to verify that a given code provides a faithful representation of the purported governing equations and corresponding solution techniques. This study provides the first cardiac tissue electrophysiology simulation benchmark to allow these codes to be verified. The benchmark was successfully evaluated on 11 simulation platforms to generate a consensus gold-standard converged solution. The benchmark definition in combination with the gold-standard solution can now be used to verify new simulation codes and numerical methods in the future.     

Urolithin as a converging scaffold linking ellagic acid and coumarin analogues: design of potent protein kinase CK2 inhibitors

Casein kinase 2 (CK2) is a ubiquitous, essential, and highly pleiotropic protein kinase; its abnormally high constitutive activity is suspected to underlie its pathogenic potential in neoplasia and other relevant diseases. Previously, using different in silico screening approaches, two potent and selective CK2 inhibitors were identified by our group: ellagic acid, a naturally occurring tannic acid derivative (K(i)=20 nM) and 3,8-dibromo-7-hydroxy-4-methylchromen-2-one (DBC, K(i)=60 nM). Comparing the crystallographic binding modes of both ellagic acid and DBC, an X-ray structure-driven merging approach was taken to design novel CK2 inhibitors with improved target affinity. A urolithin moiety is proposed as a possible bridging scaffold between the two known CK2 inhibitors, ellagic acid and DBC. Optimization of urolithin A as the bridging moiety led to the identification of 4-bromo-3,8-dihydroxy-benzo[c]chromen-6-one as a novel, potent and selective CK2 inhibitor, which shows a K(i) value of 7 nM against the protein kinase, representing a significant improvement in affinity for the target compared with the two parent fragments.     

Hydrogen production by photocatalytic membranes fabricated by supersonic cluster beam deposition on glass fiber filters

Photoactive membranes coated with TiO₂ and Pt/TiO₂ nanostructured thin films were produced by one-step deposition of gas phase nanoparticles on glass fiber filters. Pt/TiO₂ nanoparticles (0–1.5 wt.% Pt content) were produced by flame spray pyrolysis, starting from liquid solutions of the Ti and Pt precursors, and then expanded in a supersonic beam to be deposited on the filters. The nanostructured coatings were composed of crystalline nanoparticles (mainly anatase phase), without any need of post-deposition annealing. The so obtained photocatalytic membranes were tested in hydrogen production by photo-steam reforming of ethanol in an expressly set-up diffusive photoreactor. The reaction rate was found to increase with increasing the Pt content in the photoactive material, up to 1.5 wt.% Pt. The use of these membranes allowed a significant increase of the hydrogen production rate compared to that obtained with the same photoactive Pt/TiO₂ films deposited on a quartz substrate.     

Identification of elastic, dielectric, and piezoelectric constants in piezoceramic disks

Three-dimensional modeling of piezoelectric devices requires a precise knowledge of piezoelectric material parameters. The commonly used piezoelectric materials belong to the 6mm symmetry class, which have ten independent constants. In this work, a methodology to obtain precise material constants over a wide frequency band through finite element analysis of a piezoceramic disk is presented. Given an experimental electrical impedance curve and a first estimate for the piezoelectric material properties, the objective is to find the material properties that minimize the difference between the electrical impedance calculated by the finite element method and that obtained experimentally by an electrical impedance analyzer. The methodology consists of four basic steps: experimental measurement, identification of vibration modes and their sensitivity to material constants, a preliminary identification algorithm, and final refinement of the material constants using an optimization algorithm. The application of the methodology is exemplified using a hard lead zirconate titanate piezoceramic. The same methodology is applied to a soft piezoceramic. The errors in the identification of each parameter are statistically estimated in both cases, and are less than 0.6% for elastic constants, and less than 6.3% for dielectric and piezoelectric constants.     

Optimization of the enzymatic esterification of diglycerol and lauric acid

In recent years, a number of industrial applications for lipases in biotransformation of fatty acids and lipids have been developed. One of the main reasons for this growing interest is the reduced overall catalyst cost owing to the development of commercially available immobilized enzymes, using polymeric carriers that facilitate recovery and reuse of the catalyst. Additional benefits for industrial applications include the specificity of the enzyme and the mild processing conditions. Diglycerol resulting from the dimerization of glycerol may replace molecules such as propylene glycol as the hydrophilic moiety of surfactants. Also, diglycerol fatty acid esters are useful as biodegradable nonionic surfactants for food, cosmetics, and pharmaceuticals. In this study, the enzymatic esterification of diglycerol and lauric acid has been optimized in a solvent-free system. The reaction was carried out in a stirred batch reactor with a vacuum pump in order to shift the equilibrium toward the products. The commercial lipase Novozym-435 was chosen as the most suitable catalyst, and the initial acid/alcohol ratio was always 1∶1. The reaction of lauric acid and diglycerol leveled off at equilibrium conversion after approximately 1 h of reaction. Previous work indicated that only temperature and catalyst concentration had significant effects on the conversion, and a full two-factorial design has proved effective in the study of the influence of these two variables on the process. The temperature range studied was 63–77°C, and the range of the catalyst concentration was 0.2–5.8 wt%. Both catalyst concentration and temperature were found to be significant factors in the esterification process, and their influences are positive. The effect of the interaction between temperature and catalyst concentration was small. A first-order approach could not fit the data adequately, and a model that included quadratic effects was required. A second-order model was developed to predict the yield of ester as a function of the variables. Analysis of residuals showed that the model predicted accurately the acid conversion over the experimental range considered. This model is useful to determine the optimal operating conditions for the industrial process. Presented in part at the 91st Annual Meeting of the AOCS in San Diego, April 2000.     

Intracellular silver accumulation in Chlamydomonas reinhardtii upon exposure to carbonate coated silver nanoparticles and silver nitrate

The intracellular silver accumulation ({Ag}(in)) upon exposure to carbonate coated silver nanoparticles (AgNP, 0.5-10 μM, average diameter 29 nm) and silver nitrate (20-500 nM) was examined in the wild type and in the cell wall free mutant of the green alga Chlamydomonas reinhardtii at pH 7.5. The {Ag}(in) was measured over time up to 1 h after a wash procedure to remove silver ions (Ag(+)) and AgNP from the algal cell surface. The {Ag}(in) increased with increasing exposure time and with increasing AgNP and AgNO(3) concentrations in the exposure media, reaching steady-state concentrations between 10(-5) and 10(-3) mol L(cell)(-1). According to estimated kinetic parameters, high Ag(+) bioconcentration factors were calculated (>10(3) L L(cell)(-1)). Higher accumulation rate constants were assessed in the cell wall free mutant, indicating a protective role of the cell wall in limiting Ag(+) uptake. The bioavailability of AgNP was calculated to be low in both strains relative to Ag(+), suggesting that AgNP internalization across the cell membrane was limited.     

Internal quality and antioxidants content of cold-stored red sweet peppers as affected by polyethylene bag packaging and hot water treatment

Physical (weight, firmness) and compositional (sugars, organic acids, ascorbic acid, phenolic compounds and carotenoids) changes of red sweet peppers (Capsicum annuum L.) were monitored during 21 days of cold storage (at 7.5 °C); fruits were stored without packaging, packaged in low density polyethylene bags, or after hot water dipping (53 °C for 4 min) and packaging. Packaging prevented water loss, and preserved the firmness of the fresh product. Sugars (fructose and glucose) content was practically constant throughout the whole storage time, for all treatments. A moderate accumulation of citric acid was observed during storage, but no marked effects of packaging and hot water dipping on citric and malic acid content. Ascorbic acid content slightly increased in unpackaged and packaged fruits, but not in treated+packaged peppers. Hydroxycinnamics total content seemed not to be affected by cold storage, packaging or hot water treatment, whereas glycosylated flavonoids showed somewhat lowered levels during storage, particularly in the case of unpackaged and packaged+treated fruits. Regarding carotenoids content, the effect of the considered storage conditions seemed to be much smaller than that due to ripening stage. Provitamin A content showed an increasing trend in unpackaged and packaged fruits; packaged+treated peppers were characterised by a lower retention of provitamin A and a higher level of capsanthin and cucurbitaxanthin A with respect to not treated fruits. On the whole, packaging and hot water treatment did not produce noticeable adverse effects on the majority of the examined compositional quality parameters.