Hybrid adaptive control of a dragonfly model

Dragonflies show unique and superior flight performances than most of other insect species and birds. They are equipped with two pairs of independently controlled wings granting an unmatchable flying performance and robustness.In this paper, it is presented an adaptive scheme controlling a nonlinear model inspired in a dragonfly-like robot. It is proposed a hybrid adaptive (HA) law for adjusting the parameters analyzing the tracking error. At the current stage of the project it is considered essential the development of computational simulation models based in the dynamics to test whether strategies or algorithms of control, parts of the system (such as different wing configurations, tail) as well as the complete system. The performance analysis proves the superiority of the HA law over the direct adaptive (DA) method in terms of faster and improved tracking and parameter convergence.     

Synthesis and Properties of Novel Polyimides Bearing Sulfonated Benzimidazole Pendant Groups

A new diamine monomer containing benzimidazole‐5‐sulfonic acid has been synthesised. It has been reacted, alone or mixed with diaminodiphenyl ether, with naphthalenic dianhydride to attain polynaphthalimides in which the sulfonic acid functionality is borne by pendant benzimidazole groups. The presence of sulfonic and benzimidazole groups greatly affected the physical properties of the polyimides as the novel polymers were found to be soluble in polar organic solvents and exhibited a lower thermal resistance than their non‐sulfonated counterparts. The polymer films exhibited good mechanical properties with tensile strength in the range 100–120 MPa and with moduli in the range 2.2–3.1 GPa. Sulfonic and benzimidazole groups significantly enhanced the hydrophilicity of the copolyimides, which showed water uptake up to 39%.

     

An Edible Oil Enriched with Lycopene from Pink Guava (Psidium guajava L.) Using Different Mechanical Treatments

According to the regulations of the United States Food and Drug Administration (FDA), organic solvents should be limited in pharmaceutical and food products due to their inherent toxicity. For this reason, this short paper proposes different mechanical treatments to extract lycopene without organic solvents to produce an edible sunflower oil (SFO) enriched with lycopene from fresh pink guavas (Psidium guajava L.) (FPGs). The methodology involves the use of SFO and a combination of mechanical treatments: a waring blender (WB), WB+ high-shear mixing (HSM) and WB+ ultrafine friction grinding (UFFG). The solid:solvent (FPG:SFO) ratios used in all the techniques were 1:5, 1:10 and 1:20. The results from optical microscopy and UV–vis spectroscopy showed a correlation between the concentration of lycopene in SFO, vegetable tissue diameters and FPG:SFO ratio. The highest lycopene concentration, 18.215 ± 1.834 mg/g FPG, was achieved in WB + UFFG with an FPG:SFO ratio of 1:20. The yield of this treatment was 66% in comparison to the conventional extraction method. The maximal lycopene concentration achieved in this work was significantly higher than the values reported by other authors, using high-pressure homogenization for tomato peel and several solvents such as water, SFO, ethyl lactate and acetone.     

Solids, flow systems and atomic spectroscopy

An overview of major combinations and recent applicatoons of the solids/flow systems/atomic spectroscopy trinomial is presented. Several representative examples, classified according to the role played by the solids (sample or active component of a chemical reaction or separation) are described.     

Automatic screening method for the rapid and simple discrimination between synthetic and natural colorants in foods

A simple screening method was developed to discriminate between synthetic and natural colorants present in foods in order to reduce the use of expensive instruments such as a liquid chromatograph with diode array detection. A rapid flow system was proposed in which samples containing natural and synthetic colorants in an acetic acid medium were passed through a wool/cotton column, where only synthetic colorants were retained and were then eluted with dilute ammonia. Yellow, red and green-blue-brown additives can be monitored at 400, 530 and 610 nm, respectively, with a conventional spectrophotometer. Complete discrimination (no false positives) between natural and synthetic colorants can be obtained for molar concentrations of natural colorants (in the absence of synthetic ones) up to 2000 (yellow), 2000 (red) and 10 000 (brown) times that of the detection limit (DL) of synthetic additives. The reliability of the method was established at five concentrations (between 0.5 and 3 DL) of the synthetic colorants tartrazine (yellow), erythrosin B (red) and brilliant black BN (brown). For a cut-off concentration of 2 DL, the percentage of false negatives ranges from 8 to 12%. Finally, the method was applied to screening several fruit drinks and candies for the determination of synthetic colorants with a sampling frequency of 10 h⁻¹.     

A gas chromatographic flow method for preconcentration and determination of vitamins D2 and D3 in pharmaceutical preparations

Summary A continuous-flow method that combines on-line preconcentration and isolation with gas chromatography for the direct determination of vitamins D₂ and D₃ in oily solutions is reported. A silica gel column permits preconcentration and isolation of analytes from the vitamin D matrix, although some triglyceride (ca. 25%) is also retained. To overcome problems associated with the low volatility of triglycerides, their retained fraction is further transesterified with potassium methylate to fatty acid methyl esters after elution. The proposed method was applied to the determination of vitamin D in pharmaceutical preparations.     

Atomic and electronic structure of unreduced and reduced CeO2 surfaces: a first-principles study

The atomic and electronic structure of (111), (110), and (100) surfaces of ceria (CeO2) were studied using density-functional theory within the generalized gradient approximation. Both stoichiometric surfaces and surfaces with oxygen vacancies (unreduced and reduced surfaces, respectively) have been examined. It is found that the (111) surface is the most stable among the considered surfaces, followed by (110) and (100) surfaces, in agreement with experimental observations and previous theoretical results. Different features of relaxation are found for the three surfaces. While the (111) surface undergoes very small relaxation, considerably larger relaxations are found for the (110) and (100) surfaces. The formation of an oxygen vacancy is closely related to the surface structure and occurs more easily for the (110) surface than for (111). The preferred vacancy location is in the surface layer for CeO2(110) and in the subsurface layer (the second O-atomic layer) for CeO2(111). For both surfaces, the O vacancy forms more readily than in the bulk. An interesting oscillatory behavior is found for the vacancy formation energy in the upper three layers of CeO2(111). Analysis of the reduced surfaces suggests that the additional charge resulting from the formation of the oxygen vacancies is localized in the first three layers of the surface. Furthermore, they are not only trapped in the 4f states of cerium.     

Nanodomains in a hydrophilic-hydrophobic IPN based on poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate)

The morphology of a series of hydrogels based on the interpenetration of poly(2-hydroxyethyl acrylate) and poly(ethyl acrylate) has been studied through transmission electron microscopy, TEM, atomic force microscopy, AFM, and dynamic-mechanical spectroscopy, DMA. For the TEM analysis phosphotungstic acid, PTA, was used as alternative selective staining agent to those commonly used. The good agreement between TEM and AFM images allowed us to confirm that the PTA technique is a very powerful tool for TEM analysis of these hydrogel systems. All the results show that the IPNs presented phase-separation with two kinds of microdomains: those preferentially with a hydrophilic nature and those with preferentially a hydrophobic one, of sizes that range from 30 nm to 100 nm. Each one of these domains is composed by smaller nanodomains of alternating hydrophobic and hydrophilic component ranging between 6 and 10 nm sizes, those preferentially with a hydrophilic nature having a larger proportion of hydrophilic nanodomains. The AFM images of the IPN with the highest PHEA mass fraction, x_PHEA = 0.75, suggest that the hydrophilic phase is co-continuous in the material. A disperse hydrophilic phase is found when the PHEA mass fraction is reduced up to x_PHEA = 0.38. This phase-separation is explained in terms of some characteristic parameters of the networks such as the mesh size and the number of units between cross-links. The morphology found makes the systems very attractive for cell adhesion substrates and for matrices of scaffolds in soft tissue engineering.