673 research outputs found
Formation of surfactant free microemulsions in the ternary system water/eugenol/ethanol
No full textThis works analyzes the aggregation phenomena occurring in a ternary mixture formed by two solventmutually immiscible, water and eugenol, and a third solvent that can act as co-solvent with both, thusfulfilling the requirements for the appearance of the ?pre-Ouzo? effect. The combination of visual obser-vation of the samples and GC?MS allows us to draw a ternary phase diagram for the system. DynamicLight Scattering (DLS) has provided information on the bulk aggregation occurring in the system, and alsohas given good insights in the destabilization of the pseudo-one phase region. The DLS measurementsperformed in different paths of the phase diagram have allowed us to establish a critical compositionfor destabilization of the one phase region, having equal content of the components. Stable microemul-sions can be used for solubilization of a model insecticide, opening a new route for the fabrication ofbiosustainable formulations for insecticides.Fil: Lucia, Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; ArgentinaFil: Argudo, Pablo G.. Universidad Complutense de Madrid; EspañaFil: Guzman, Eduardo. Universidad Complutense de Madrid; EspañaFil: Rubio, Ramon G.. Universidad Complutense de Madrid; EspañaFil: Ortega, Francisco. Universidad Complutense de Madrid; Españ
Equilibrium and dynamic surface properties of trisiloxane aqueous solutions. Part 2. Theory and comparison with experiment
No full textIn the first part of this paper we presented experimental results, which shows the presence of surface aggregates in aqueous solutions of trisiloxane surfactants (Ritacco et al. [1]). Formation of those aggregates has been found for those trisiloxanes (T6, T7, T8, and T9), which show superspreading behaviour at room temperature. However, the formation of surface aggregates has not been detected for trisiloxanes (T4 and T5), which do not show superspreading behaviour at room temperature. It is shown that experimental results on equilibrium and dynamic interfacial tension agree well with a combined theoretical model, which is based on reorientation (or two states) and aggregation models. According to the reorientation model there are two states of trisiloxane molecules on the surface layer: molecules in those two states occupy different surface areas. The aggregation model was modified to account for specific properties of trisiloxane molecules. According to that model molecules occupying the lowest area on the interface can form two-dimensional aggregates. It was assumed that trisiloxane molecules include two kinetically independent trimethylsilyl [-O-Si(CH3)3] groups. This assumption allowed us to agree the aggregation theoretical model and experimental data on ellipsometric measurement of adsorption. © 2010 Elsevier B.V.Fil: Ritacco, Hernán Alejandro. Universidad Complutense de Madrid; EspañaFil: Fainerman, Valentin B.. Donetsk Medical University; UcraniaFil: Ortega, Francisco. Universidad Complutense de Madrid; EspañaFil: Rubio, Ramon G.. Universidad Complutense de Madrid; EspañaFil: Ivanova, Natalia. Loughborough University; Reino UnidoFil: Starov, Victor M.. Loughborough University; Reino Unid
Modern energy consumption and economic modernisation in Latin America and the Caribbean between 1890 and 1925
No full textIn the absence of comparable macroeconomic indicators for most of the Latin American economies before the 1930s, the apparent consumption of energy is used in this paper as a proxy of the degree of modernisation of Latin America and the Caribbean. This paper presents an estimate of the apparent consumption per head of modern energies (coal, petroleum and hydroelectricity) for 30 countries of Latin American and the Caribbean for 1890 to 1925, multiplying the number of countries for which energy consumption estimates were previously available. As a result, the paper provides the basis for a quantitative comparative analysis of modernisation performance beyond the few countries for which historical national accounts are available in Latin America.Energy consumption, economic modernisation, Latin America
The ℓ <sup>s</sup>-boundedness of a family of integral operators on UMD banach function spaces
No full textWe prove the ℓs-boundedness of a family of integral operators with an operator-valued kernel on UMD Banach function spaces. This generalizes and simplifies earlier work by Gallarati, Veraar and the author, where the ℓs-boundedness of this family of integral operators was shown on Lebesgue spaces. The proof is based on a characterization of ℓs-boundedness as weighted boundedness by Rubio de Francia.Analysi
Physico-chemical challenges on the self-assembly of natural and bio-based ingredients on hair surfaces: towards sustainable haircare formulations
No full textPolymers and surfactants are used in many technological and industrial applications such as the manufacture of functional materials and coatings, personal care and pharmaceutical products, food science, paints, anti-icing fluids, tertiary oil recovery and the paper industry. Polymer–surfactant mixtures are particularly important in shampoos and conditioners. However, as in almost every other industry over the past five or more decades, the performance of hair care formulations has been significantly improved by the use of petrochemical-derived ingredients. As a result, cosmetic formulations, and hair care formulations in particular, have been based primarily on polymers and surfactants that are neither renewable, nor derived from environmentally friendly processes, nor have a positive environmental impact. This contrasts with the extensive use of natural and renewable products, mainly plant extracts, in cosmetics in ancient times. Therefore, the substitution of currently used ingredients with others of natural origin has been a top priority for the cosmetic industry over the last two decades, and in order to achieve greater consumer acceptance, it is crucial to maintain and, where possible, improve the technical performance of such products. This paper describes the complexities and challenges of developing greener shampoo and conditioner ingredients and formulations to meet current and future needs, and outlines a methodological approach based on model hair surfaces and a selection of appropriate experimental and numerical techniques to achieve our goals. Some encouraging technical routes using biosurfactants, biopolymers and bio-based polymers are presented, along with the significant opportunity to obtain a wide range of green ingredients through molecular design and well-controlled biotechnological processes. Similar concerns apply to other cosmetic products such as waxes, fragrances, bleaching agents, etc.Depto. de Química FísicaFac. de Ciencias QuímicasTRUEpubDescuento UC
Análisis del comportamiento del gasto público social en salud, educación y vivienda para la ciudad de Cartagena; período 1995 - 1997
No full textTesis (Economista) -- Universidad de Cartagena. Facultad de Ciencias Económicas. Programa de Economía. 1998.El presente estudio tiene por objeto analizar las características del comportamiento del G. P. S en salud, educación y vivienda para la ciudad de Cartagena durante el periodo 1995 - 1997
The internal and external flow fields of a structured porous coated cylinder and implications on flow-induced noise
No full textPorous coated cylinders have been shown to reduce the vortex shedding tone and broadband noise of a bare cylinder placed in uniform flow within specific Reynolds number regimes. The processes by which the vortex shedding and thus tone suppression take place are still uncertain despite numerous numerical and experimental studies. It is understood that adding a porous medium to a bare cylinder will have an influence on the Reynolds number of cylinder, yet the increase of outer diameter alone and the influences of surface roughness are insufficient to explain the changes in the shedding tone magnitude and frequency that are observed by many. Investigating the internal flow field of a porous coated cylinder could lead to a deeper understanding of the flow processes that result in the tonal noise reduction. This has not been achieved to date, as commonly used materials such as metal foam and polyurethane possess randomized porous structures, which make investigating the internal flow field nearly impossible without affecting the structure itself. This paper presents a preliminary analysis of the internal and external flow fields of two structured porous coated cylinders. The cylinders were manufactured using solid transparent materials that possess direct lines of sight through the pores in the axial and spanwise directions. Such structured porous coated cylinders have been previously successful in reducing the typical vortex shedding tone. Tomographic and 2-D planar Particle Image Velocimetry (PIV) were used in a water-tunnel facility to visualize the internal and external flow fields. To date only the 2-D planar PIV results have been post-processed that reveal differences in the wake for the two different cylinder types such as recirculation of flow around the pores. Vorticity flow structures are observed to vary along the cylinder span in the same pattern as the porous structure and streamlines at the windward cylinder side reveal the entry of flow into the porous medium.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Aircraft Noise and Climate EffectsWind Energ
Critical wetting concentrations of trisiloxane surfactants
No full textTrisiloxane surfactants also known as "superspreaders" are characterized by a critical wetting concentration (CWC) which has been determined by Svitova et al [T. Svitova, R.M. Hill, Y. Smirnova, A. Stuermer, G. Yakubov, Langmuir 14 (1998) 5023-5031]. CWC is a concentration above which a transition from partial wetting to complete wetting occurs at spreading over moderately hydrophobic surfaces, hence, the CWC is associated with the beginning of the superspreading. The latter shows that the knowledge of the CWCs is important for many wetting/spreading applications. We suggest a new method, which allows determining CWCs for a range of trisiloxanes using wetting behaviour of aqueous trisiloxane solutions on highly hydrophobic smooth Teflon AF coated silicon wafers. Using the new method the CWCs for trisiloxane surfactants, Tn with a wide range in the number (n = 4-9) of ethylene oxide units have been measured. The critical aggregation concentration (CAC) for trisiloxane surfactants has been measured using the surface tension methods. Additionally, spreading kinetics of all trisiloxane surfactants studied over moderately hydrophobic substrates has been investigated. It has been found that for all trisiloxanes studied the CWCs are several times higher than their corresponding CAC values. The CWCs for T6 and T8 trisiloxanes obtained according to our approach are in agreement with those measured by Svitova et al. [T. Svitova, R.M. Hill, Y. Smirnova, A. Stuermer, G. Yakubov, Langmuir 14 (1998) 5023-5031] for the case of complete wetting. It has been verified that indeed at CWCs estimated according to our approach trisiloxane surfactant solutions demonstrate superspreading behaviour on moderately hydrophobic surfaces with the exception of trisiloxane T4, which still shows only partial wetting. Thus, the CWC does not depend on the degree of hydrophobicity of substrates and could be considered as a distinct property of surfactants that characterize the highest limit of their spreading capability. Crown Copyright © 2009.Fil: Ivanova, Natalia. University Of Loughborough; Reino UnidoFil: Starov, Victor. University Of Loughborough; Reino UnidoFil: Rubio, Ramon. Universidad Complutense de Madrid; EspañaFil: Ritacco, Hernán Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Complutense de Madrid; EspañaFil: Hilal, Nidal. The University of Nottingham; Reino UnidoFil: Johnson, Daniel. The University of Nottingham; Reino Unid
PESI - a taxonomic backbone for Europe
No full textThis is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
The attached file is the published version of the article.NHM Repositor
Internal shear layer and vortex shedding development of a structured porous coated cylinder using tomographic particle image velocimetry
No full textVortex shedding in the wake of a cylinder in uniform flow can be suppressed via the application of a porous coating; however, the suppression mechanism is not fully understood. The internal flow field of a porous coated cylinder (PCC) can provide a deeper understanding of how the flow within the porous medium affects the wake development. A structured PCC (SPCC) was three-dimensionally printed using a transparent material and tested in water tunnel facilities using flow visualisation and tomographic particle image velocimetry at outer-diameter Reynolds numbers of and, respectively. The internal and near-wall flow fields are analysed at the windward and mid-circumference regions. Flow stagnation is observed in the porous layer on the windward side and its boundary is shown to fluctuate with time in the outermost porous layer. This stagnation region generates a quasi-aerodynamic body that influences boundary layer development on the SPCC inner diameter, that separates into a shear layer within the porous medium. For the first time via experiment, spectral content within the separated shear layer reveals vortex shedding processes emanating through single pores at the outer diameter, providing strong evidence that SPCC vortex shedding originates from the inner diameter. Velocity fluctuations linked to this vortex shedding propagate through the porous layers into the external flow field at a velocity less than that of the free stream. The Strouhal number linked to this velocity accurately predicts the SPCC vortex shedding frequency.Wind Energ
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