Rheological properties of pectin-enriched products isolated from butternut (Cucurbita moschata Duch ex Poiret)

Rheological behavior of five different pectin-enriched products obtained from a cell wall enriched powder of butternut (Cucurbita moschata Duch ex Poiret) was evaluated through flow and oscillatory assays. The product SE was obtained through treatment with citrate buffer; C1 and C2 were obtained using cellulase and different enzyme-substrate ratios while H1 and H2 resulted from hemicellulase treatment at different levels. SE- and H1-pectin-enriched fractions showed the best performance as thickeners as indicated by their highest Newtonian viscosities and time constants on shear-thinning along the flow. These fractions showed a structure with the highest density of interactions between the hydrated macromolecules when solutions were evaluated at rest. Fractions obtained with a higher activity of hemicellulase (H2) or with the lowest activity of cellulase assayed (C1) showed the same degree of structure when evaluated at rest, while C2-fraction presented the lowest density of macromolecular interactions in water, behaving as a diluted hydrocolloid solution as confirmed by its fitting to the Cox-Merz rule. Molecular weight distribution of polysaccharide fractions along with chemical composition helped to explain the rheological behavior of these isolated fractions which contained between 39 and 78 g of galacturonic acid per 100 g of product. With the exception of C2 fraction, pectin-enriched products isolated from butternut showed an interesting range of thickening properties and can be used as thickeners in the food industry.     

Influence of carbonate intercalation in the surface-charging behavior of Zn–Cr layered double hydroxides

The influence of interlayer composition in the surface charge and reactivity of layered double hydroxides (LDHs) has been explored. With this purpose, a chloride-intercalated Zn–Cr-LDH has been synthesized by the constant pH coprecipitation method and afterwards exchanged with carbonate to obtain solids with different Cl^?/CO₃^2? ratios. The solids structure has been characterized by elemental chemical analysis, powder X-ray diffraction and infrared spectroscopy, while its surface-charging behavior and reactivity have been studied by acid–base potentiometric titrations and electrophoretic mobility determinations. The chloride-intercalated sample shows an increasing hydroxyl adsorption with increasing pH and decreasing support electrolyte concentration and the particles present positive electrophoretic mobility in the measured pH range. As carbonate content increases in the samples, the total OH^? uptake diminishes and the samples show an isoelectric point at pH around 10. When the gallery is totally occupied by carbonate anions, the OH uptake vs. pH curves registered at different electrolyte concentrations merge at around pH 10. A LDH–water interface model has been used to give an interpretation to the experimental data. The model indicates that as carbonate content increases, the sample behavior becomes similar to that of a metal (hydr)oxide and that surface (bi)carbonate anions undergo acid–base reactions.     

Role of perfluorosulfonic ionomer as protective agent against strong adsorption of (bi)sulfate anions. Relevance in the determination of the area of Pt/C electrocatalysts

This work aims to shed light on the wide dispersion of the values of the area of Pt/C electrodes reported when evaluated by means of the thin-film electrode approach. The effect of the Perfluorosulfonic Ionomer (PFSI) content of the electrodes and the nature of the electrolyte are discussed. The results disclose that the area of the Pt electrodes evaluated by electrochemical techniques is related to the actual PFSI content on the electrode and to the nature of the electrolyte. Using HClO₄ as electrolyte, electrode area values are independent of the PFSI content. On the contrary, if experiments are recorded in H₂SO₄, the electrode area value increases with the increasing PFSI content, irrespectively of the Pt loading. Such effect is ascribed to the interaction of the sulfonic groups from the PFSI with the surface of the Pt nanoparticles, avoiding the strong adsorption of the bisulfate anions.     

The road to RoboCup 2050

The ultimate goal of the RoboCup initiative is stated as follows: by mid-21st century, a team of fully autonomous humanoid robot soccer players shall win the soccer game, comply with the official rule of the FIFA, against the winner of the most recent World Cup. The authors consider this goal from the perspective of how close we are to it and what has to be done to reach it     

How the free limbs are used by elite high jumpers in generating vertical velocity

The aim of this study was to quantify how elite high jumpers used their free limbs in a competitive high jump and to estimate the contribution that these made to vertical take-off velocity. This was achieved by analysing the competitive performances of six elite male high jumpers using 3D motion analysis and assessing limb function using the relative momentum method. The mean peak relative momentum of the arm nearest to the bar at take-off was 9.4 kg m s(-1), while that of the arm furthest away from the bar was 11.3 kg m s(-1) and these did not differ significantly. The free (lead) leg reached a mean peak relative momentum of 20.9 kg m s(-1). At touch-down the free leg had a large positive relative momentum that was offset by the negative relative momentum of the arms, although their combined value still remained positive. The mean combined free limbs' relative momentum at touch-down was 13.8 kg m s(-1) and reached a peak of 37.6 kg m s(-1). The difference between these two values amounted to 7.1 % of whole-body momentum, which was judged to be the amount by which the free limbs contributed to performance. The arms had a greater influence on performance than had the lead leg. This was because the lead leg increased its relative momentum little during the contact period while the arms had an initial negative value that increased markedly after touch-down. The compressive force exerted by the motion of the free limbs, estimated by the change in the combined free limbs' relative momentum, reached a mean peak of 366 N and was greatest at 37% of the contact period. It was concluded that to maximize the contribution the free limbs can make to performance, given the restraints imposed on technique by other performance requirements, the arms should have a vigorous downward motion at touch-down to make the most use of the high (but little changing) relative momentum of the lead leg.     

Tuberculin reactivity in the elderly. Comparison of PPD-RT23 and PPD-CT68

BACKGROUND: Tuberculin reactivity varies on the basis of the PPD lot and the population studied. AIMS: To compare tuberculin reactivity in the elderly following successive applications of PPD from 2 different lots. POPULATION: Elderly nursing-home residents, from the province of Guadalajara, Spain. METHODS: The elderly were randomly selected and administered with a first Mantoux intradermoreaction of 2 UT of PPD-RT23 or 2 UT of PPD-CT68. The study was performed in a scaled basis, eliminating the reactors (transversal induration > or = 5 mm at 72 h). The non reactors were restudied with a second and third test in alternative arms at a 7-day interval with the same lot and initial dosis of PPD. At one year the scaled study was repeated with 2 UT of PPD-CT68. RESULTS: Eight hundred and thirty elderly persons (79 +/- 9 years) were studied, with 410 receiving PPD-RT23 and 420 receiving PPD-CT68. No differences were observed in the percentage of initial reactors (31% vs 29%; p = 0.26) or in the booster reactors (23% vs 20%; p = 0.16). The PPD-RT23 was found to trigger more intensive reactions than the PPD-CT68 leading to a greater frequency of indurations > 14 mm. After one year, the percentage of stable reactions was similar in both groups (50.5% vs 49.5%; NS). CONCLUSIONS: 1) In elderly nursing-home residents 2 UT of PPD-RT23 and 2 UT of PPD-CT68 showed similar results in regard to the number of reactors and the frequency of booster reactions. 2) The proportion of intense reactions was greater with 2 UT of PPD-RT23 than with 2 UT of PPD-CT68. 3) The stability of the reactions at one year was independent of the lot used in the first phase.     

A sliding mode control proposal for open-loop unstable processes

This papers presents a sliding mode controller based on a first-order-plus-dead-time model of the process for controlling open-loop unstable systems. The proposed controller has a simple and fixed structure with a set of tuning equations as a function of the desired performance. Both linear and nonlinear models were used to study the controller performance by computer simulations.     

Nitrogen adsorption method for determining the mesopore slit-like size distribution of expansive soils

One of the most important structural parameters involved in the characterization of the void space of soils is the pore size distribution. In this work, a nitrogen adsorption method is presented as an alternative to determine the mesopore contribution of slit-shaped pores to the abovementioned parameter in montmorillonite-containing soils. The mesopore size structural parameter obtained via this sorption method is related to montmorillonite d₀₀₁ interlayer distances proceeding from either X-ray or electron diffraction analysis, if only by assuming during sorption analysis that mesopores resident inside clay grains adopt slit-shaped geometries. Mineralogical analysis and determination of some important geotechnical properties of these montmorillonite-containing soils complement the preceding sorption and structural studies.