Rotating Hele-Shaw cells with ferrofluids

We investigate the flow of two immiscible, viscous fluids in a rotating Hele-Shaw cell, when one of the fluids is a ferrofluid and an external magnetic field is applied. The interplay between centrifugal and magnetic forces in determining the instability of the fluid-fluid interface is analyzed. The linear stability analysis of the problem shows that a non-uniform, azimuthal magnetic field, applied tangential to the cell, tends to stabilize the interface. We verify that maximum growth rate selection of initial patterns is influenced by the applied field, which tends to decrease the number of interface ripples. We contrast these results with the situation in which a uniform magnetic field is applied normally to the plane defined by the rotating Hele-Shaw cell.Comment: 12 pages, 3 ps figures, RevTe

Formulation and optimization of emulsions based on bitter fennel essential oil and EO/BO block copolymer surfactant

The influence of EO/BO block copolymer surfactant concentration in the range (1–5% (m/m)) and emulsification time on the emulsion stability and droplet size distribution of bitter fennel essential oil-in-water emulsions has been studied. Essential oils are promising material to be used for emulsion formulation with applications in cosmetics, food industry and agrochemicals. In the latter field these emulsions may be used as matrices for pesticides, where essential oils play the role of an eco-friendly solvent. A two-factor central composite design was conducted in order to optimize the emulsion formulation and processing. Emulsion stability has been studied as function of ageing time, by multiple light scattering (Turbiscan Lab-expert, Formulaction) and laser diffraction (Mastersizer X, Malvern). The surface response methodology allowed us to obtain a formulation comprising minimum droplet size and maximum stability by using a single step rotor/stator homogenization process. Creaming turned out to be the main destabilization mechanism. In order to improve emulsion stability the influence of high pressure homogenization (M110P, Microfluidics, MA, USA) and addition of a weighting agent (rosin gum) was studied. Although lower droplet sizes were obtained in both cases (D3,2 were in the range 0.30–0.35 μm), emulsions were more unstable maybe due to Ostwald ripening phenomena.(Project CTQ2015-70700-P) from theSpanish Ministerio de Economía y CompetitividadEuropean Commission (FEDER Programme)Bordas Chinchurreta and KA

Multi-objective optimisation of product quality in the manufacture of Ti-6AI-4V prostheses

[EN] This paper presents a multi-objective optimisation procedure for optimising the quality of prostheses and manufacturing productivity. The aim of this procedure is to develop machining performance models through a minimal and progressive Design of Experiment (DoE), which models the variables of interest by linear regressions or Surface Response Models (SRMs). The multi-objective optimisation is based on desirability functions, which are defined according to the relative importance of each variable of interest. The procedure was implemented to optimise a process of manufacturing spherical turned components for Ti-6Al-4V hip prostheses with special requirements as regards surface roughness Ra, Rz and geometrical form toleranceThis work has been partially supported by Fundació Caixa-Castelló Bancaixa under the research project INV-2009-39. The authors are grateful to Miguel Angel Aymerich and Arcadi Sanz, who assisted in the experimental part. The authors extend their acknowledgements to Lafitt Company for its collaboration. Additional support was provided by Tecnológico de Monterrey through the research group in Mechatronics and Intelligent Machines.Abellán Nebot, JV.; Siller Carrillo, HR.; Vila, C.; Rodríguez González, CA. (2010). Multi-objective optimisation of product quality in the manufacture of Ti-6AI-4V prostheses. Journal of Manufacturing Technology Research. 5(3):353-369. https://doi.org/10.1504/IJMR.2010.033471S3533695

Expression of a plastid-targeted flavodoxin decreases chloroplast reactive oxygen species accumulation and delays senescence in aging tobacco leaves

Leaf senescence is a concerted physiological process involving controlled degradation of cellular structures and reallocation of breakdown products to other plant organs. It is accompanied by increased production of reactive oxygen species (ROS) that are proposed to signal cell death, although both the origin and the precise role of ROS in the execution of this developmental program are still poorly understood. To investigate the contribution of chloroplast-associated ROS to natural leaf senescence, we used tobacco plants expressing a plastid-targeted flavodoxin, an electron shuttle flavoprotein present in prokaryotes and algae. When expressed in plants, flavodoxin specifically prevents ROS formation in chloroplasts during stress situations. Senescence symptoms were significantly mitigated in these transformants, with decreased accumulation of chloroplastic ROS and differential preservation of chlorophylls, carotenoids, protein contents, cell and chloroplast structures, membrane integrity and cell viability. Flavodoxin also improved maintenance of chlorophyll-protein complexes, photosynthetic electron flow, CO2 assimilation, central metabolic routes and levels of bioactive cytokinins and auxins in aging leaves. Delayed induction of senescence-associated genes indicates that the entire genetic program of senescence was affected by flavodoxin. The results suggest that ROS generated in chloroplasts are involved in the regulation of natural leaf senescence.Instituto de Fisiología Vegeta

Métodos de investigación en las ponencias y comunicaciones presentadas en los simposios de la SEIEM

En este artículo se analizan los métodos de investigación utilizados en las ponencias y comunicaciones presentadas en los simposios de la SEIEM, desde su constitución en 1997 hasta 2010. Se estudia la distribución temporal, método de investigación preferente, área problemática, nivel educativo y principales características metodológicas, comparando con otros informes en los que se analizan los métodos de investigación en educación matemática. Así mismo se describen las características de los trabajos que aplican métodos cuantitativos, cualitativos y mixtos, y se proporciona una guía de reflexión metodológica, junto con algunas recomendaciones para incrementar el rigor metodológico en la investigación en educación matemática

Métodos de investigación en Educación Matemática: análisis de los trabajos publicados en los simposios de la SEIEM (1997-2010)

En esta ponencia se describe el planteamiento general del seminario sobre métodos de investigación celebrado en el XV Simposio de la Sociedad Española de Investigación en Educación Matemática (SEIEM). Se ha realizado un estudio cualitativo y cuantitativo de los trabajos presentados en los Simposios de la SEIEM desde su constitución en 1997 hasta 2010, desde el punto de vista de los métodos de investigación usados en dichos trabajos, así como otras variables relacionadas. En esta ponencia conjunta se describen los resultados globales obtenidos y se comparan con resultados de otros estudios relacionados en los que se analizan los métodos de investigación en educación matemática. Los análisis detallados de los métodos cuantitativos, cualitativos y mixtos son objeto de tres ponencias específicas, presentadas, asimismo, en el Seminario

Molecular Simplification in Bioactive Molecules: Formal Synthesis of (+)-Muconin

7 páginas, 1 figura, 7 esquemas, 1 tabla.-- El PDF es la versión post-print.The concept of molecular simplification as a drug design strategy to shorten synthetic routes, while keeping or enhancing the biological activity of the lead drug, has been applied to (+)-muconin, an acetogenin with remarkable cytotoxicity. A novel approach that enables the stereoselective synthesis of such a natural compound or its enantiomer from a common precursor is described. An additional advantage of the method is complete stereochemical control and the decrease in the number of chemical steps required, thus providing an enhancement of the overall yield. Antiproliferative studies against the human solid tumor cell lines showed that the aliphatic chain-THF/THP fragment of (+)-muconin has modest cytotoxic activity. The strategy opens the way to preparing novel bioactive acetogenin analogues by shorter synthetic routes.The authors thank the MYCT (PPQ2002- 04361-C04-02) of Spain and the Canary Islands Government for supporting this research. F.R.P.C. thanks CajaCanarias for a FPI fellowship. R.C. thanks the Spanish MEC for a FPU fellowship. J.M.P. thanks ICIC for a postdoctoral fellowship.Peer reviewe

Olive Leaves as Biotemplates for Enhanced Solar-Light Harvesting by a Titania-Based Solid

Olive leaves (by-product from olive oil production in olive mills) were used as biotemplates to synthesize a titania-based artificial olive leaf (AOL). Scanning electron microscopy (SEM) images of AOL showed the successful replication of trichomes and internal structure channels present in olive leaves. The BET surface area of AOL was 52 m2·g−1. X-ray diffraction (XRD) and Raman spectra revealed that the resulting solid was in the predominantly-anatase crystalline form (7.5 nm average particle size). Moreover, the synthesis led to a red-shift in light absorption as compared to reference anatase (gap energies of 2.98 and 3.2 eV, respectively). The presence of surface defects (as evidenced by X-ray photoelectron spectroscopy, XPS, and electron paramagnetic resonance spectroscopy, EPR) and doping elements (e.g., 1% nitrogen, observed by elemental analysis and XPS) could account for that. AOL was preliminarily tested as a catalyst for hydrogen production through glycerol photoreforming and exhibited an activity 64% higher than reference material Evonik P25 under solar irradiation and 144% greater under ultraviolet radiation, (under voltage) UV

Gravity-driven instability in a spherical Hele-Shaw cell

A pair of concentric spheres separated by a small gap form a spherical Hele-Shaw cell. In this cell an interfacial instability arises when two immiscible fluids flow. We derive the equation of motion for the interface perturbation amplitudes, including both pressure and gravity drivings, using a mode coupling approach. Linear stability analysis shows that mode growth rates depend upon interface perimeter and gravitational force. Mode coupling analysis reveals the formation of fingering structures presenting a tendency toward finger tip-sharpening.Comment: 13 pages, 4 ps figures, RevTex, to appear in Physical Review