Synchronization and local convergence analysis of networks with dynamic diffusive coupling

In this paper, we address the problem of achieving synchronization in networks of nonlinear units coupled by dynamic diffusive terms. We present two types of couplings consisting of a static linear term, corresponding to the diffusive coupling, and a dynamic term which can be either the integral or the derivative of the sum of the mismatches between the states of neighbouring agents. The resulting dynamic coupling strategy is a distributed proportional-integral (PI) or a proportional-derivative (PD) law that is shown to be effective in improving the network synchronization performance, for example, when the dynamics at nodes are nonidentical. We assess the stability of the network by extending the classical Master Stability Function approach to the case where the links are dynamic ones of PI/PD type. We validate our approach via a set of representative examples including networks of chaotic Lorenz and networks of nonlinear mechanical systems

A classical and semiclassical study of collisions between Xq+ ions and water molecules

Collisions of He2+, Li3+ and C3+ ions with water molecules are studied at energies ranging between 20 keV u-1 and 500 keV u-1. Three methods are employed: the classical trajectory Monte Carlo (CTMC), the expansion of the scattering wave function in terms of asymptotic frozen molecular orbitals (AFMO) and a lattice method to numerically solve the time-dependent Schrödinger equation (GridTDSE). Total cross sections for single ionization, single electron capture, transfer ionization and electron production are calculated and compared with previous close-coupling calculations and experiments. The fragmentation branching ratios are discussedThis work has been partially supported by Ministerio de Economía and Competitividad (Spain), project no. FIS2017-84684-

A review of issues in seagrass seed dormancy and germination: implications for conservation and restoration

Seagrasses have received considerable attention over the past 2 decades because of the multiple ecological roles they play in estuarine and coastal ecosystems and concerns over worldwide losses of seagrass habitat due to direct and indirect human impacts. Restoration and conservation efforts are underway in some areas of the world, but progress may be limited by the paucity of information on the role of seeds in bed dynamics. Although flowering occurs in most of the 58 seagrass species, seed germination data exist for only 19 of the 42 species that have some period of dormancy, with only 93 published references to field and/or laboratory studies. This review addresses critical issues in conservation and restoration of seagrasses involving seed dormancy (e.g. environmental vs physiological), existence and type of seed bank (transient or persistent), and factors influencing seed germination (e.g, salinity, temperature, light). Results of many earlier published studies relating seed germination to various environmental factors may need re-examination given more recent published data which show a confounding influence of oxygen level on the germination process. We highlight the importance of conducting ecologically meaningful germination studies, including germination experiments conducted in sediments. We also identify questions for future research that may figure prominently in landscape level questions regarding protected marine or estuarine reserves, habitat fragmentation, and restoration

Capítulo 8: Acuerdos comerciales regionales y sus efectos en la inversión extranjera directa para América Latina: Una aproximación desde el modelo de gravedad

Los años 80 se caracterizaron por una marcada expansión de los mercados internacionales en la forma de Inversión Extranjera Directa (en adelante IED) (Kahouli & Maktouf, 2015). Posteriormente, en la década de los 90, los Acuerdos Comerciales Regionales (ACR) comienzan a proliferar en América Latina gracias a las políticas aperturistas que caracterizaron dicho periodo (Aguilera et al., 2017). Varios ACR contienen un capítulo de inversión en el cual se plantean condiciones y características para promover la inversión en distintos sectores entre países miembros, por lo que se esperaría un aumento en la IED después de la entrada en vigencia de un ACR. Dicho esto, el presente capítulo plantea un modelo de gravedad para determinar el impacto que los ACR han tenido en la IED bilateral, con datos de la Conferencia de las Naciones Unidas sobre Comercio y Desarrollo (UNCTAD, por sus siglas en inglés), de 26 países de América Latina y el Caribe, durante el período de 1990 a 2017. Como es costumbre en modelos básicos de gravedad, las variables de control incluyen distancia, el tamaño del país -tanto emisor como receptor de IED- (PIB real), y el poder adquisitivo de la población –también en ambas economías- (PIB per cápita). Los resultados muestran una relación positiva y significativa de los flujos de IED con el PIB; una relación positiva con el PIB per cápita del país emisor y negativa con aquel del país receptor; y una relación negativa con la distancia entre los países socios. La existencia de ACR aparece como significativa solo en el período de 1990 a 1999 que, como se señaló anteriormente, coincide con el período de apertura económica de la región

Changes in melatonin concentrations in seminal plasma are not correlated with testosterone or antioxidant enzyme activity when rams are located in areas with an equatorial photoperiod

In temperate climates, photoperiod and melatonin regulate ram reproduction, modulating hormonal secretions, sperm quality, and seminal plasma composition. Information on the effect of an equatorial photoperiod (12L:12D) on ram reproduction, however, is scarce, and no data on hormonal concentrations and antioxidant enzyme activity in seminal plasma have been reported. Thus, the variation was investigated of melatonin and its relationship with testosterone and antioxidant enzyme activity in the seminal plasma of three sheep breeds in Colombia, when there was a consistent photoperiod during two dry and two rainy seasons per year. Semen was collected once a week from 12 mature rams (four of each breed: Colombian Creole, Hampshire, and Romney Marsh). Seminal plasma was obtained by centrifugation. The concentration of melatonin and testosterone were quantified along with the enzymatic activity of glutathione peroxidase (GPx), glutathione reductase (GRD), and catalase (CAT). Correlation analyses between melatonin and testosterone concentrations or enzymatic activity were also performed. Melatonin concentration was affected by season (P < 0.05) but not breed, with lesser concentrations in the first rainy season. Testosterone concentration, however, was affected by breed and season, with greater concentrations (P < 0.01) in the Hampshire and Romney Marsh rams during the second dry season. Regarding antioxidant enzyme activity, there was only seasonal variation in GPx activity (P < 0.05). When correlation analyses were used for data assessments, there was a negative correlation between melatonin and testosterone concentrations in Hampshire rams. In conclusion, melatonin concentrations in seminal plasma of rams that were located in an area with an equatorial photoperiod was affected by the climatological season but there was no positive correlation with testosterone concentration or antioxidant enzyme activity

Vasectomy and photoperiodic regimen modify the protein profile, hormonal content and antioxidant enzymes activity of ram seminal plasma

This work aimed to determine the contribution of the testis and epididymis and the effect of the photoperiodic regimen on ram seminal plasma (SP). Semen was collected from 15 mature rams located in an equatorial (Colombian Creole and Romney Marsh, eight intact and two vasectomized) or a temperate climate (Rasa Aragonesa, three intact and two vasectomized). SP proteins were analyzed by Bradford, SDS-PAGE and difference gel electrophoresis (DIGE). Melatonin and testosterone concentrations were quantified by ELISA, and activity of glutathione peroxidase (GPx), glutathione reductase (GRD), and catalase by enzymatic assays. Vasectomy increased protein concentration and the intensity of high molecular weight bands (p < 0.001), with no differences between breeds. DIGE revealed the absence of six proteins in vasectomized rams: angiotensin-converting enzyme, lactotransferrin, phosphoglycerate kinase, sorbitol dehydrogenase, epididymal secretory glutathione peroxidase and epididymal secretory protein E1. Vasectomy also decreased melatonin concentrations in seasonal rams, and testosterone in all of them (p < 0.001), but did not affect antioxidant enzyme activity. Equatorial rams showed lower melatonin and testosterone concentration (p < 0.01) and catalase, but higher GPx activity (p < 0.05). In conclusion, vasectomy modifies the protein profile and hormonal content of ram seminal plasma, whereas the exposure to a constant photoperiod affects hormonal concentration and antioxidant enzymes activity

VOLUMEN 18, NÚMERO 32 (1989)

MODELO PRELIMINAR DE SEDIMENTACIÓN ACTUAL EN EL GRABEN COLOMBO - ECUATORIANO. Padilla, L. E.; León, L. A.ASPECTOS GEOLÓGICOS Y GEOMORFOLÓGICOS DE COMO EL RÍO CAUCA CORRÍA HACIA EL SUR. Padilla, L. E.; León, L. A.ESTUDIO TEXTURAL Y COMPOSICIONAL DE SEDIMENTOS ACTIVOS DEL RÍO MAGDALENA, ENTRE NEIVA Y BOCAS DE CENIZA. Castiblanco, C. R.; Lombana, P. E.APPLICATION OF SCANNING ELECTRON MICROSCOPE AND X-RAY MICROANALYSIS TECHNIQUES IN THE EVALUATION OF RESERVOIR QUALITY AND PETROLEUM PRODUCTION PROBLEMS. Reyes, R.; Pinzón, P.TÉCNICAS DE EVALUACIÓN DE PROYECTOS CARBONÍFEROS. Ortega, C