Computation of bounded feed-forward control for underactuated multibody systems using nonlinear optimization

Underactuation occurs, when only some generalized coordinates have a control input. For end-effector trajectory tracking a combined feed-forward and feedback control is often a suitable approach. Feed-forward control design based on an inverse model for underactuated multibody systems is presented. The starting point is the transformation of the multibody system into a nonlinear input-output normal-form. The inverse model follows from this and consists of chains of differentiators, driven internal dynamics and an algebraic part. Especially when using the end-effector as system output the internal dynamics is often unbounded. In order to obtain a viable feed-forward control, a bounded solution must be determined. For this task the internal dynamics is solved as a nonlinear optimization problem. Thereby, the coordinates of the internal dynamics define the objective function which is minimized. The equation of the internal dynamics must be fulfilled at each point of a discrete time grid. In addition continuity of the solution is achieved by adding as equality constraint an integration formula, e.g. trapezoidal rule. The optimization problem is then solved by a SQP-method. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical interpretation of switching in experiments with single molecules

Identifying the factors that trigger current-switching behavior of single molecules establishes the means by which it may be possible to tailor these molecules to perform as electronic devices. We provide a theoretical interpretation of switching observed in recent experiments with single molecules using quantum chemistry tools. We conclude that the switching observed in the experiment is mostly due to conformational changes and that some charge changes cannot be observed in STM experiments.     

Variability in phenolic composition of Hypericum androsaemum

The methanolic extracts of fifteen Hypericum androsaemum samples, growing spontaneously or cultivated in Portugal, were analysed by HPLC/DAD, allowing the identification of 9 phenolic compounds and the detection of 6 phloroglucinols. Total amounts of phenolics found ranged from 11 to 39 g/kg, and the influence of some factors which may be responsible for this variation is discussed. The individual compounds were also quantified. Four different phenolic profiles were found concerning both qualitative and quantitative composition, indicating the possible existence of chemical polymorphism.     

Limits for the central production of Theta+ and Xi(--)pentaquarks in 920-GeV pA collisions

We have searched for Theta+(1540) and Xi(--)(1862) pentaquark candidates in proton-induced reactions on C, Ti, and W targets at midrapidity and square root of s = 41.6 GeV. In 2 x 10(8) inelastic events we find no evidence for narrow (sigma approximately 5 MeV) signals in the Theta+ --> pK0(S) and Xi(--) --> Xi- pi- channels; our 95% C.L. upper limits (UL) for the inclusive production cross section times branching fraction B dsigma/dy/(y approximately 0) are (4-16) mub/N for a Theta+ mass between 1521 and 1555 MeV, and 2.5 mub/N for the Xi(--). The UL of the yield ratio of Theta+/Lambda(1520) < (3-12)% is significantly lower than model predictions. Our UL of B Xi(--)/Xi(1530)0 < 4% is at variance with the results that have provided the first evidence for the Xi(--).     

Continuum thermo-mechanical model for homogeneous liquid–gas flows with internal surface tension effects

This work presents a rational thermodynamic model which consistently incorporates internal surface tension effects in homogeneous and isothermal two-component two-phase flows, without appealing to additional kinematical variables to describe its microstructure. The liquid and gaseous phases are regarded as a pseudo-fluid whose constitutive behavior is obtained from two thermodynamic potentials—the Helmholtz free energy and a pseudo-potential of dissipation. The structure of the flow is assumed to be described solely by the void fraction, which is treated as an internal variable. The constraint associated with it is regarded as a material property, being an effective part of the constitutive equations. Surface tension is taken by the model into account by adding a suitable extra term, with dependence on the void fraction, in the Helmholtz free energy. The capability of the proposed model in properly describing pertinent physical phenomenon is demonstrated by comparing the analytical predictions of sound speeds in the medium with available experimental data.     

Chiral Capillary Electrokinetic Chromatography: Principle and Applications,Detection and Identification,Design of Experiment,and Exploration of Chiral Recognition Using Molecular Modeling

This work reviews the literature of chiral capillary electrokinetic chromatography from January 2016 to March 2021. This is done to explore the state-of-the-art approach and recent developments carried out in this field. The separation principle of the technique is described and supported with simple graphical illustrations, showing migration under normal and reversed polarity modes of the separation voltage. The most relevant applications of the technique for enantioseparation of drugs and other enantiomeric molecules in different fields using chiral selectors in single, dual, or multiple systems are highlighted. Measures to improve the detection sensitivity of chiral capillary electrokinetic chromatography with UV detector are discussed, and the alternative aspects are explored, besides special emphases to hyphenation compatibility to mass spectrometry. Partial filling and counter migration techniques are described. Indirect identification of the separated enantiomers and the determination of enantiomeric migration order are mentioned. The application of Quality by Design principles to facilitate method development, optimization, and validation is presented. The elucidation and explanation of chiral recognition in molecular bases are discussed with special focus on the role of molecular modeling.     

Novel polyurethanes from xylan and TDI: Preparation and characterization

Xylan is a hemicellulose, which is found abundantly in nature. In this work, a novel polyurethane was developed involving xylan and tolylene-2,4-diisocyanate (TDI). Polymer synthesis was achieved through conventional heat or microwave-assisted reaction in dimethyl sulfoxide. Because xylan has multiple OH groups on each polymer chain, the TDI/xylan molar ratio had to be adjusted to produce a soluble polymeric product. The reaction products were characterized by ¹³C NMR, FTIR, thermogravimetric analysis, and differential scanning calorimetry. The xylan polyurethane was shown to exhibit improved thermal stability over xylan.     

The use of ultrasound in the extraction of Ilex paraguariensis leaves: a comparison with maceration

The objective of this work is to discuss the main parameters that influence the sonication extraction of Ilex paraguariensis leaves. For this purpose, the extraction time, solvent polarity, solvent volume, sample mass and particle size were evaluated. Results showed that the main variable affecting the extraction process was the solvent polarity. Though in a less extent, temperature and extraction time also demonstrated to be important parameters, while the other variables did not present a significant influence on the extraction yield. The extracts at the optimized condition were compared with those obtained by maceration, in terms of mass yield and chemical composition. The major compounds identified in the extracts were caffeine and palmitic acid. Some saturated hydrocarbons such as fatty acids, fatty acid methyl esters, phytosterols, and theobromine were also identified in the fractions.     

Effect of the corona treatment and of the 1,4-cyclohexanedimethanol on the surface characteristics of the poly(ethylene terephthalate) film

Several techniques have been applied for the characterization of three PET films surfaces: homopolymer PET film, corona treated PET film and a poly(ethylene terephthalate-co-1,4-cyclohexanedimethanol) film. The objective of this work is to investigate and to apply precise and mutually complementary techniques which give detailled information about theses surfaces, as there are few papers with global and conclusive results. The film surfaces were investigated to support the development of new products and envisage new apllications to the existent films. Scanning electron micrographs, attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) and multiple internal reflection Fourier transform infrared spectroscopy (FTIR-MIR) spectra show that the chemical composition, topography and surface roughness of the films are different. The corona-treated PET film shows high surface tension value due to the major contribution on the polar groups and oxidation level acquired. The copolyester film is much less crystalline than the other films analyzed, as demonstrated by refractive index measurements and X-ray photoelectron spectroscopy (XPS). The amorphous structures obtained and the high tension level of the corona-treated films provide a better understanding of the adhesion phenomena. In view of results obtained, one can assume that corona treated films owing to its higher surface tension and films with CHDM owing to its surface amorphization should provide manufacturing industries better processing conditions than films without surface treatment and also higher levels of adhesion to paints and coatings.