Mixing in convective thermal fluxes in unsteady nonhomogeneous flows generating complex three dimensional vorticity patterns

Diffusion and scaling of the velocity and vorticity in a thermoelectric driven heating and cooling experimental device is presented in order to map the different patterns and transitions between two and three dimensional convection in an enclosure with complex driven flows. The size of the water tank is of 0.2 x 0.2 x 0.1 m and the heat sources or sinks can be regulated both in power and sign [1-3]. The thermal convective driven flows are generated by means of Peltier effects in 4 wall extended positions of 0.05 x 0.05 cm each. The parameter range of convective cell array varies strongly with the Topology of the boundary conditions. Side heat and momentum fluxes are a function of Rayleigh, Peclet and Nusselt numbers, [4-6] Visualizations are performed by PIV, Particle tracking and shadowgraph. The structure of the flow is shown by setting up a convective flow generated by buoyant heat fluxes. The experiments described here investigate high Prandtl number mixing using brine and fresh water in order to form a density interface and low Prandtl number mixing with temperature gradients. The evolution of the mixing fronts are compared and the topological characteristics of the merging of the convective structures are examined for different configurations. Based on two dimensional Vorticity spectral analysis, new techniques can be very useful to determine the evolution of scales considering the multi-fractal structure of the convective flows.Peer ReviewedPostprint (published version

Fermi surface renormalization in Hubbard ladders

We derive the one-loop renormalization equations for the shift in the Fermi-wavevectors for one-dimensional interacting models with four Fermi-points (two left and two right movers) and two Fermi velocities v_1 and v_2. We find the shift to be proportional to (v_1-v_2)U^2, where U is the Hubbard-U. Our results apply to the Hubbard ladder and to the t_1-t_2 Hubbard model. The Fermi-sea with fewer particles tends to empty. The stability of a saddle point due to shifts of the Fermi-energy and the shift of the Fermi-wavevector at the Mott-Hubbard transition are discussed.Comment: 5 pages, 4 Postscript figure

The segmentation of the Canarian tourism market with regared to expenditure: an empirical study of La Palma

In the context of the European Union countries, the Canary Islands have presented and continue to do so, unquestionable comparative and competitive advantages as supplier of tourism products that have lead to, driven more by managerial initiative and foreign capital than by the desire and initiative of the local population, a truly monocultural tourism production. The strong expansion of the services sector that tourism development has produced in parallel constitutes a logical consequence of an activity such as tourism characterised to be basic (Begg, 1993), that is to say, to present very strong effects on other economic activities. It is in fact the economic importance of tourism in the Canary Islands that has lead local authorities to consider the maintenance and improvement of competitiveness levels in tourism in the field of the domestic and international market (Government of Canaries, 1998). The maintenance and improvement of competitiveness levels depend on the segmentation of tourism supply as means of responding to, on one hand, greater competition in prices in the tourist markets of homogeneous products, especially in the sector of sun and beach, and on the other hand, the appearance of an increasing demand for more customised services, where the tourist outlines his/her leisure time requirements in an individual way which ultimately changes the essence of the homogeneous tourist package that the tour-operator has traditionally offered. In this paper we use, therefore, a focus on the segmented markets in which a range of tourism products exists, each one of which satisfies, to greater or lesser extent, the needs of a segment of demand. We have two objectives, firstly, to identify those segments of current demand acquired at destination and, secondly, to determine, amongst them the niches associated with greater expense, in order to profile lines of a regional policy of innovation in products that it embraces them and generates greater levels of local development. Thus we will analyse several sources of data. On the one hand, data which comes from the Survey of Tourist Expenditure carried out by the Institute of Statistics of the Canary Islands and on the other, information obtained in an empirical study carried out over the last few years and referring especially to the island of La Palma. Specifically, we will establish two expenditure segments: lower and middle, to thus determine the characteristics that identify tourists included in the bracket of highest expenditure at destination

Monitoring of evoked potentials during spinal cord ischaemia: Experimental evaluation in a rabbit model

Objectives:somatosensory evoked potentials (SEPs), spinal evoked potentials (Spinal-EPs), and motor-evoked potentials (MEPs) were monitored in a rabbit model of spinal cord ischaemia to evaluate their accuracy and relationship to clinical status.Methods:a modified rabbit spinal cord ischaemia model of infrarenal aortic occlusion for 21 min was employed (30 rabbits). After baseline SEPs, Spinal-EPs, and MEPs were obtained, evoked potentials were recorded continuously during and after clamping of the aorta (30 min). Neurological outcome at 24 h was correlated with evoked potentials, and histopathological findings.Results:fifteen animals became paraplegic. MEPs were always abolished after clamping of the aorta while Spinal-EPs and SEPs remained. The sensory evoked potentials (SEPs and Spinal-EPs) were the least sensitive to spinal cord ischaemia, and their presence had no correlation with the final clinical status (50% of false negatives). This was consistent with histopathological examination that showed damage almost entirely confined to the anterior horn, while the dorsal columns were generally well preserved. High spine MEPs evoked by twitch stimulation was the best predictor of clinical outcome (0% of false negatives, 0% of false positives).Conclusions:SEPs and Spinal-EPs cannot be used as safe monitors of ischaemia of the spinal cord. High spine MEPs evoked by twitch stimulation was the most useful for real-time evaluation of spinal cord ischaemia, and the best predictor of neurologic outcome during reperfusion

Long-Circulating Hyaluronan-Based Nanohydrogels as Carriers of Hydrophobic Drugs

[EN] Nanohydrogels based on natural polymers, such as polysaccharides, are gaining interest as vehicles for therapeutic agents, as they can modify the pharmacokinetics and pharmacodynamics of the carried drugs. In this work, hyaluronan-riboflavin nanohydrogels were tested in vivo in healthy rats highlighting their lack of toxicity, even at high doses, and their different biodistribution with respect to that of native hyaluronan. They were also exploited as carriers of a hydrophobic model drug, the anti-inflammatory piroxicam, that was physically embedded within the nanohydrogels by an autoclave treatment. The nanoformulation was tested by intravenous administration showing an improvement of the pharmacokinetic parameters of the molecule. The obtained results indicate that hyaluronan-based self-assembled nanohydrogels are suitable systems for low-soluble drug administration, by increasing the dose as well as the circulation time of poorly available therapeutic agents.Financial support from University Sapienza Progetti di Ricerca: grant RP116154C2EF9AC8 and grant RM11715C1743EE89 are acknowledged. Isabel Gonzalez-Alvarez, Marta Gonzalez-Alvarez and Marival Bermejo acknowledge partial financial support to project SAF2016-78756 from MINECO (Spanish Ministry of economy, industry and competitivity). Mayte Martinez-Martínez received a grant from the Ministry of Education and Science of Spain (FPU13-01105).Di Meo, C.; Martínez Martínez, M.; Coviello, T.; Bermejo, M.; Merino Sanjuán, V.; Gonzalez-Alvarez, I.; Gonzalez-Alvarez, M.... (2018). Long-Circulating Hyaluronan-Based Nanohydrogels as Carriers of Hydrophobic Drugs. Pharmaceutics. 10(4):1-15. https://doi.org/10.3390/pharmaceutics10040213S115104Allison, D. 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PLGA nanoparticles are effective to control the colonic release and absorption on ibuprofen. European Journal of Pharmaceutical Sciences, 115, 119-125. doi:10.1016/j.ejps.2017.12.009Samiei, N., Mangas-Sanjuan, V., González-Álvarez, I., Foroutan, M., Shafaati, A., Zarghi, A., & Bermejo, M. (2013). Ion-pair strategy for enabling amifostine oral absorption: Rat in situ and in vivo experiments. European Journal of Pharmaceutical Sciences, 49(4), 499-504. doi:10.1016/j.ejps.2013.04.025Wei, X., Senanayake, T. H., Bohling, A., & Vinogradov, S. V. (2014). Targeted Nanogel Conjugate for Improved Stability and Cellular Permeability of Curcumin: Synthesis, Pharmacokinetics, and Tumor Growth Inhibition. Molecular Pharmaceutics, 11(9), 3112-3122. doi:10.1021/mp500290