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Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Photonic fi lters can be used for filtering the spectrum of wide-band optical sources such as light emitting diodes (LED) or multimode laser diodes (MMLD). In this work the use of birefringent optical media such as polarization maintaining fiber (PMF) or birefringent optical waveguides on Lithium Niobate (LiNbO3) crystal, perform as optical fi lters. The birefringent optical media, used as optical retarders, modify the optical spectrum by "channelizing" them. These devices act as photonic filters, thus modifying an optical spectrum. As reported in this paper, integrated optics photonic filters are easily implemented by birefringent optical waveguides on LiNbO3 electrooptic crystals. The practical filtering of LED and MMLD spectra is demonstrated in this work. The photonic fi lters can be used for implementing microwave filters or optoelectronic multiplexing for radio or radio over fiber schemes. [ABSTRACT FROM AUTHOR]

This paper considers the prescribed scalar curvature problem on the sphere for n ≥ 3. Given a prescribed scalar curvature function K : Sn → R and a centered dilation defined by Fy = Σ-1 o Dβ o Σ, y ϵ Bn+1, where Σ is the stereographic projection and Dβ is a dilation in Rn, in this work we estimate the gradient of the function K near the critical point of the function J¯p(y) = ∫Sn K(ζ)ϕp+1dσ(ζ) where ϕ(y) = ∣(F-1y )∫∣ n-2/2 . We will use this estimate to find Lp estimates of the first two y-derivatives of the function K o Fy(ξ). [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper we analyze asymptotic stability of the dynamical system x = f(x) defined by a C¹ function f : D Rn where D Rn + is an open set. We obtain a criterion of stability for the equilibrium solution x D when the vector field f satisfies a) ifi(x) < 0 and b) (ifi(x))-1 ifj(x) + (jfj(x))-1 jfi(x) > 2 for i, j = 1, . . .,n. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper we study a dark energy model taking into account a non-linear interaction between the dark energy and dark matter components. The non-linear interaction term, used in this work, is proportional to the square of dark energy density. Considering a FRW type flat universe, we obtain an analytical expression for the Hubble parameter H and from this quantity, the deceleration parameter q and the equation of state parameter wΛ are analyzed. We found that, in this scenario, the accelerated expansion regime of the universe in late times is possible. However, using suitable values for the coupling constant, the square of the speed of sound remains negative, therefore, the model is unstable under small perturbations. [ABSTRACT FROM AUTHOR]

Searching for new antioxidants used in pharmaceuticals, cosmetics or agrochemicals have increased today. Many phenolic compounds have been reported as promising for this goal. Melastomataceae is rich in these compounds. Consequently, in this research the antioxidant power for Meriania nobilis and M. hernandoi ( Melastomataceae) was compared. Both species were extracted in acetone 70%. The latest was liquid-liquid partitioned in ethyl acetate (Mn or Mh 2.1), n-butanol (Mn or Mh 2.2) and aqueous fractions (Mn or Mh 2.3). Antioxidant activity was measured by DPPH free radical scavenging method (FRS50, mg.L-1), ferric reducing antioxidant power assay (FRAP, mg FeSO4.7H2O (100 g)-1ES) and total phenolic content (TPC, mg AG g-1ES) by Folin-Ciocalteu. The present study revealed that Mh 2.1 and Mh 2.2 from M. hernandoi have a strong antioxidant power FRS50 = 5.71±0.085, FRAP = 53±1.5 and TPC = 224±7.1 and FRS50 = 4.22±0.001, FRAP = 65 mg±1.5, TPC = 240 ±8.6 respectively, as compared with positive control, quercetin DPPH FRS50 = 4.20±0.410, FRAP = 61±1.3. M. nobilis exhibited poor antioxidant power FRS50 = 286±1.5, FRAP = 2.01±0.079 and TPC = 26±1.5. This paper showed M. hernandoi as good source of antioxidant compounds with potential usage as cosmetic, pharmaceutical or agrochemical ingredients. [ABSTRACT FROM AUTHOR]

In the present paper we introduce a new hierarchy, each equation of which is defined by several brackets of two pseudodifferential operators. We dealwith some algebraic properties of these equations. In particular, we show that, as in the classic case, they are related to the presence of an infinite sequence of first integrals. A new version of the Zakharov-Shabattype equations is proved. Formal solutions of this hierarchy are constructedusing a "several brackets bilinear identity". [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this paper we find lower bounds for the first Steklov eigenvalue in Riemannian a-manifolds, a = 2, 3, with non-positive sectional curvature. [ABSTRACT FROM AUTHOR]

Electrodes with dimensions in the micro- and nanometer scale can be used as analytical probes in confined places such as cells and organelles. Arrays of microelectrodes, particularly disk-shaped electrodes, are now a platform to fabricate electrochemical sensors and multisensors. A useful characteristic of such arrays is that enhancement of the current signal is due to the fact that radial diffusion becomes important as the disk radius gets smaller and steady state currents are attainable in a relatively short time. Because there is no general analytical solution for the current response at MEAs, previous characterization of any micro electrode array at hand is still required. This paper discusses the electrochemical characterizat ion of the mass transport of a reversible electrochemical probe at a commercially available micro-disk electrode array by two commonly used tools for electro analysis, namely: cyclic voltammetry and chronoamperometry. The questions to be addressed are whether clear radial diffusion control can be effectively achieved and the time required for the electrode system to reach steady state. For chronoamperometric experiments, the current response almost achieves steady state in the time range between 0.49 s and 1 s. This is precisely the time bracket in which analytical measurements should be made in order to achieve high sensitivity. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents preliminary results on the design, construction and evaluation of a passive mini direct ethanol fuel cell (DEFC), capillary fed with 2 mol l-1 aqueous ethanol, at a rate of 2.03 µL min-1, and air oxygen in the cathode through an air vent. Parameters such as pressure, temperature and time of manufacturing a membrane-electrode assembly (MEA) by hot-pressure were evaluated. As the electrode holder used a 0.25 cm² carbon tissue which was deposited on the catalytic layer (C. L.) for both the anode (0.8 mg cm-2 of PtRu/C) and the cathode (0.8 mg cm-2 of Pt/C), Nafi on® 115 membranes were used as the electrolyte. The results show, an average power density of 302 µWcm² under the best conditions used, a catalytic layer with a Nafi on percentage of 50% at 25 °C. A temperature of 125 °C, a pressure of 49.2 Kg/cm², and 90 seconds duration were used to obtain the MEA. [ABSTRACT FROM AUTHOR]

In this paper, we summarize the four main ice nucleating aerosol types: mineral dusts, bioaerosols, soot, and glassy organics, with the aim of demonstrating the limitations in scientific literature regarding their ice nucleation properties. Because the tropics are largely associated with marine environments, such as the Atlantic, Pacific, and Indian Oceans, they are potential source of ice nuclei, and therefore ice clouds can form in regions of high convective uplift. As a result, these particles are able to influence both the planet's radiative balance and its hydrological cycle. Due to our limited understanding of these effects, we would like to encourage the scientific community to increase its efforts to study and characterize the tropical aerosol particles that may function as ice nuclei. Through such efforts, we may reduce uncertainties in climate predictions, and improve our understanding of global warming in the hopes of fi nding potential solutions to these issues. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Insufficient access to potable water is becoming one of the major threats to sustainable development around the globe. The implementation of water conservation policies and the use of mature and novel desalination technologies are key to address the water demand for an increasing population. Desalination systems based on electrochemical cells are of current interest. This paper discusses an electrochemical cell based on carbon electrodes modified with polypyrrole and a polypyrrole/polystyrene sulfonate composite which have anion and cation exchange properties, respectively. The cell was used to substantially decrease the concentration of sodium chloride solution in the 10-1 and the 10-2 M concentration range. The long term stability of this cell is also discussed. [ABSTRACT FROM AUTHOR]

In this paper, we discuss a novel method based on a quantum-information-tool suitable to identify and characterize quantum-phases and phase transitions in a broad set of lattice models relevant in condensed-matter systems. The method relies on the entanglement entropy which, for instance, can be calculated using the Matrix Product State (MPS) algorithm, or any other method, for several system sizes to perform an appropriate scaling. Particularly, this advanced method has been applied for a finite 1D system of repulsively interacting spin-1 bosons and obtaining the universality class via the calculation of the central charge for the extemal field-induced phase transition between the dimerized phase and the XY-nematic phase in the antiferromagnetic regime. Finally, we briefly discuss how this method has been recently used to identify topological phases. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We explore the effects of the transition-state vibrational motions on the dynamics of the reaction X + HY [XHY] XH + Y with X and Y = Br, I. We performed simulations of the dissociation process of the unstable XHY complex using a classical trajectory methodology, combined with London-Eyring-Polanyi-Sato (LEPS) potentials to approximate the interactions among the atoms in XHY. We employed an almost classical sampling scheme on the stable XHY- species to obtain the initial conditions for the trajectories by assuming a vertical transition to the XHY neutral potential energy surface. To study the effects of the vibrations, we considered different sets of initial conditions reflecting specific XHY normal mode excitations. We found an increase in the rotational energies of the product diatoms with an increase in the energy associated to the bending normal modes of XHY. Analysis of the vibrational distributions of the diatoms shows higher most probable vibrational quantum numbers for HBr when compared to HI. For some initial conditions, we also found approximately thermal rotational distributions in the product diatoms. [ABSTRACT FROM AUTHOR]

Essential oils from pipilongo seeds (Piper tuberculatum) was extracted using supercritical carbon dioxide. The extraction was performed as a function of particle size of the grinded seeds. The highest yield (2,812%) was obtained with the smallest particle size. The chemical composition analysis of the oil by GC-MS led to identify 15 compounds, some of which are β-elemene, caryophyllene, β-farnesene, neophytadiene and piperine among others. The microbicide activity of the essential oil was determined by Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) assays, showing that the growth of the bacteria Staphylococcus aureus and Bacillus subtilis was inhibited, and hence with a possible microbicidal effect, whereas for pseudomonas aeruginosa and Salmonella typhimurium showed no effect on their growth. [ABSTRACT FROM AUTHOR]

Determining the antioxidant activity and the total phenolic content are routine procedures in most natural product laboratories; however, when dealing with large number of samples, it is necessary to employ methods that allow a quick, easy and economical screening. The aim of this study is to determine the antioxidant activity and the total phenolic content of plant species as criteria for the selection of promising species. To reach this aim, we used twenty species from Yotoco National Protected Forest in Valle del Cauca, Colombia. The species Clidemia tococoidea and Miconia aeruginosa, showed the highest total phenolic content together with the best antioxidant activity in terms of DPPH radical scavenging activity. The excellent correlation (R2=0.9610) shown between these parameters, demonstrated the utility of the process used as a method for primary screening and selection of promising species for phytochemical analysis at a preparative scale for this two assays. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Revista de Ciencias is the property of Universidad del Valle and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)