Controlling chaotic transport in two-dimensional periodic potentials

We uncover and characterize different chaotic transport scenarios in perfect two-dimensional periodic potentials by controlling the chaotic dynamics of particles subjected to periodic external forces in the absence of a ratchet effect i.e., with no directed transport by symmetry breaking of zero-mean forces . After identifying relevant symmetries of the equations of motion, analytical estimates in parameter space for the occurrence of different transport scenarios are provided and confirmed by numerical simulations. These scenarios are highly sensitive to variations of the system’s asymmetry parameters, including the eccentricity of the two-dimensional periodic potential and the direction of dc and ac forces, which could be useful for particle sorting purposes in those cases where chaos is unavoidablePostprint (published version

Dilute gas viscosity of n-alkanes represented by rigid Lennard-Jones chains

The shear viscosity in the dilute gas limit has been calculated by means of the classical trajectory method for a gas consisting of chain-like molecules. The molecules were modelled as rigid chains made up of spherical segments that interact through a combination of site-site Lennard-Jones 12-6 potentials. Results are reported for chains consisting of 2, 3, 4, 6, 8, 12 and 16 segments in the reduced temperature range of 0.3 – 50 for site-site separations of 0.25 , 0.333 , 0.40 , 0.60 and 0.80 , where is the Lennard-Jones length scaling parameter. The results were used to determine the shear viscosity of n-alkanes in the zerodensity limit by representing an n-alkane molecule as a rigid linear chain consisting of c − 1 spherical segments, where c is the number of carbon atoms. We show that for a given n-alkane molecule, the scaling parameters ε and σ are not unique and not transferable from one molecule to another. The commonly used site-site Lennard-Jones 12-6 potential in combination with a rigid-chain molecular representation can only accurately mimic the viscosity if the scaling parameters are fitted. If the scaling parameters are estimated from the scaling parameters of other n-alkanes, the predicted viscosity values have an unacceptably high uncertainty

Hierarchical Self-Assembly of Halogen-Bonded Block Copolymer Complexes into Upright Cylindrical Domains

Self-assembly of block copolymers into well-defined, ordered arrangements of chemically distinct domains is a reliable strategy for preparing tailored nanostructures. Microphase separation results from the system, minimizing repulsive interactions between dissimilar blocks and maximizing attractive interactions between similar blocks. Supramolecular methods have also achieved this separation by introducing small-molecule additives binding specifically to one block by noncovalent interactions. Here, we use halogen bonding as a supramolecular tool that directs the hierarchical self-assembly of low-molecular-weight perfluorinated molecules and diblock copolymers. Microphase separation results in a lamellar-within-cylindrical arrangement and promotes upright cylindrical alignment in films upon rapid casting and without further annealing. Such cylindrical domains with internal lamellar self-assemblies can be cleaved by solvent treatment of bulk films, resulting in separated and segmented cylindrical micelles stabilized by halogen-bond-based supramolecular crosslinks. These features, alongside the reversible nature of halogen bonding, provide a robust modular approach for nanofabricatio

El teorema de Abel para la lemniscata

En este artículo demostramos el teorema de Abel para la lemniscata sin la ayuda de la teoría de las funciones elípticas y sin referencia alguna a la moderna teoría de campos. Los ingredientes esenciales de la demostración son las funciones lemniscáticas de Gauss y algunas nociones elementales sobre factorización en el anillo de los polinomios con coeficientes racionales. El procedimiento es muy poderoso. En verdad, no sólo probamos que la construcción geométrica es posible, sino que indicamos las operaciones algebraicas que realizan la construcción

Advanced surface characterization of silver nanocluster segregation in Ag-TiCN bioactive coatings by RBS, GDOES and ARXPS

Surface modification by means of wear protective and antibacterial coatings represents, nowadays, a crucial challenge in the biomaterials field in order to enhance the lifetime of bio-devices. It is possible to tailor the properties of the material by using an appropriate combination of high wear resistance (e.g., nitride or carbide coatings) and biocide agents (e.g., noble metals as silver) to fulfill its final application. This behavior is controlled at last by the outmost surface of the coating. Therefore, the analytical characterization of these new materials requires high-resolution analytical techniques able to provide information about surface and depth composition down to the nanometric level. Among these techniques are Rutherford backscattering spectrometry (RBS), glow discharge optical emission spectroscopy (GDOES), and angle resolved X-ray photoelectron spectroscopy (ARXPS). In this work, we present a comparative RBS–GDOES–ARXPS study of the surface characterization of Ag–TiCN coatings with Ag/Ti atomic ratios varying from 0 to 1.49, deposited at room temperature and 200 °C. RBS analysis allowed a precise quantification of the silver content along the coating with a non-uniform Ag depth distribution for the samples with higher Ag content. GDOES surface profiling revealed that the samples with higher Ag content as well as the samples deposited at 200 °C showed an ultrathin (1–10 nm) Ag-rich layer on the coating surface followed by a silver depletion zone (20–30 nm), being the thickness of both layers enhanced with Ag content and deposition temperature. ARXPS analysis confirmed these observations after applying general algorithm involving regularization in addition to singular value decomposition techniques to obtain the concentration depth profiles. Finally, ARXPS measurements were used to provide further information on the surface morphology of the samples obtaining an excellent agreement with SEM observations when a growth model of silver islands with a height d = 1.5 nm and coverage θ = 0.20 was applied to the sample with Ag/Ti = 1.49 and deposited at room temperature.This work was financially supported by the Spanish Ministry of Science and Innovation (projects FUNCOAT CSD2008-00023 and RyC2007-0026). This research is sponsored by FEDER funds through the program COMPETE "Programa Operacional Factores de Competitividade" and by national funds through FCT "Fundacao para a Ciencia e a Tecnologia", in the framework of the Strategic Projects PEST-C/FIS/UI607/2011, and PEST-C/EME/UI0285/2011 and under the project PTDC/CTM/102853/2008. The authors would like to acknowledge I. Caretti and R. Velasco for the fruitful discussions and the proofreading of the manuscript

Guidelines for oral assessment

En este documento se presentan los lineamientos y teoría para la implementación de un sistema de evaluación oral en el Centro de Idiomas de la Universidad Eafit. El texto desarrolla tres temas principales: 1) el enfoque comunicativo para la enseñanza y la evaluación ; 2) la planeación de la evaluación; y 3) el uso de las herramientas de evaluación.This document aims at offering teachers a framework for assessing oral language and some guidelines that will foster the implementation and practice of a homogeneous oral assessment system (OAS) at the EAFIT University Language Center. The document deals with three main topics, namely (1) Communicative Approach to Teaching and Assessment; (2) Planning for Assessment; and (3) Using the Oral Assessment Rubric

Kv2.1 channels play opposing roles in regulating membrane potential, Ca2+ channel function, and myogenic tone in arterial smooth muscle.

The accepted role of the protein Kv2.1 in arterial smooth muscle cells is to form K+ channels in the sarcolemma. Opening of Kv2.1 channels causes membrane hyperpolarization, which decreases the activity of L-type CaV1.2 channels, lowering intracellular Ca2+ ([Ca2+]i) and causing smooth muscle relaxation. A limitation of this model is that it is based exclusively on data from male arterial myocytes. Here, we used a combination of electrophysiology as well as imaging approaches to investigate the role of Kv2.1 channels in male and female arterial myocytes. We confirmed that Kv2.1 plays a canonical conductive role but found it also has a structural role in arterial myocytes to enhance clustering of CaV1.2 channels. Less than 1% of Kv2.1 channels are conductive and induce membrane hyperpolarization. Paradoxically, by enhancing the structural clustering and probability of CaV1.2-CaV1.2 interactions within these clusters, Kv2.1 increases Ca2+ influx. These functional impacts of Kv2.1 depend on its level of expression, which varies with sex. In female myocytes, where expression of Kv2.1 protein is higher than in male myocytes, Kv2.1 has conductive and structural roles. Female myocytes have larger CaV1.2 clusters, larger [Ca2+]i, and larger myogenic tone than male myocytes. In contrast, in male myocytes, Kv2.1 channels regulate membrane potential but not CaV1.2 channel clustering. We propose a model in which Kv2.1 function varies with sex: in males, Kv2.1 channels control membrane potential but, in female myocytes, Kv2.1 plays dual electrical and CaV1.2 clustering roles. This contributes to sex-specific regulation of excitability, [Ca2+]i, and myogenic tone in arterial myocytes

Self-rated health in Europe and its determinants: Does generation matter?

Objectives: To analyse the influence of micro- and macro-factors on self-rated health, and the role of generation on this relationship. Methods: Cross-sectional study using data from European Health Interview Surveys from 14 European countries. Individuals were divided into four generations (“silent generation”, “baby boomers”, and “generation X” and “Y”). We conducted multilevel analyses for each generation to study the influence of individual and national explanatory variables on self-rated health. Results: Age showed an exponential effect in older generations. Education and employment presented the strongest association with low self-rated health, especially in “baby boomers” and women (low education: OR 3.5; 95% CI 3.2–3.9). Tobacco showed a negative effect in younger generations. Overweight and low physical activity were negatively associated with self-rated health regardless of generation. Countries from the Eastern welfare system showed the highest risk of low self-rated health and this association was higher in men for “silent generation” (OR 4.7; 95% CI 3.0–7.6). Conclusions: The influence of individual and national factors on self-rated health varies regarding generation. The target generation and the demographic structure of a country should be taken into account to develop more accurate health policies

Desarrollo de una metodología para el establecimiento in vitro de Limoncillo (Swinglea glutinosa)

Esta investigación se realizó en el Laboratorio de Biotecnología Vegetal de la Facultad de Ciencias Agropecuarias de la Universidad de Panamá, durante los meses de octubre del 2018 y junio de 2019. El objetivo fue el de evaluar la respuesta de Swinglea glutinosa (limoncillo) a la micropropagación, a través de ápices y yemas axilares provenientes de la germinación in Vitro de semillas gámicas y su respuesta ante la presencia de reguladores de crecimiento (Ácido giberélico, Bencilaminopurina y Ácido Indolbutírico). Estas semillas para su desinfección fueron sumergidas en una solución de Hipoclorito de Sodio (NaCLO) a una concentración de 1.25% durante distintos tiempos de inmersión (15 y 30 minutos). Se utilizó un diseño completamente al azar. Para las tres etapas se utilizó el medio básico Murashige y Skoog (1962) suplementado con reguladores de crecimiento: Ácido Giberélico (1 mg/l, 2 mg/l, 3 mg/l), Bencilaminopurina (1mg/l, 2 mg/l), Ácido Indolbutírico (0.1 mg/l). El efecto de los tratamientos fue evaluado durante cada una de las etapas del cultivo in vitro (Establecimiento y Multiplicación). Los mejores resultados para el efecto desinfectante del Hipoclorito de Sodio (NaCLO) se lograron con una inmersión de 30 minutos. El análisis de varianza realizado mediante el sistema computacional SAS: En la etapa de establecimiento el tratamiento que mayor altura de planta alcanzó fue AG 1 ppm con una media de 4.54cm. Se encontraron diferencias altamente significativas en la producción de hojas y brotes con la aplicación de BAP (1, 2) ppm en la etapa de Multiplicación. La mayor tasa de producción de brotes se alcanzó en el primer subcultivo con un Coeficiente de Multiplicación (CM) de 2.63