University of Los Andes

About: University of Los Andes is a education organization based out in Bogotá, Colombia. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17616 authors who have published 25555 publications receiving 413463 citations.

Recurrent coronal jets induced by repetitively accumulated electric currents

Abstract: Context. Jets of plasma are frequently observed in the solar corona. A self-similar recurrent behavior is observed in a fraction o f them. Aims. Jets are thought to be a consequence of magnetic reconnection, however, the physics involved is not fully understood. Therefore, we study some jet observations with unprecedented temporal and spatial resolutions. Methods. The extreme-ultraviolet (EUV) jets were observed by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory(SDO). The Helioseismic and Magnetic Imager (HMI) on board SDO measured the vector magnetic field, from which we derive the magnetic flux evolution, the photosp heric velocity field, and the vertical electric current evol ution. The magnetic configuration before the jets is derived by the nonl inear force-free field (NLFFF) extrapolation. Results. Three EUV jets recurred in about one hour on 2010 September 17 in the following magnetic polarity of active region 11106. We derive that the jets are above a pair of parasitic magnetic bipoles which are continuously driven by photospheric diverging flows. The interaction drove the build up of electric currents that we indeed observed as elongated patterns at the photospheric level. For the first time, the high temporal cadence of HMI allows to follow t he evolution of such small currents. In the jet region, we found that the integrated absolute current peaks repetitively in phas e with the 171 A flux evolution. The current build up and its dec ay are both fast, about 10 minutes each, and the current maximum precedes the 171 A by also about 10 minutes. Then, HMI temporal cadence is marginally fast enough to detect such changes. Conclusions. The photospheric current pattern of the jets is found associ ated to the quasi-separatrix layers deduced from the magnetic extrapolation. From previous theoretical results, the obs erved diverging flows are expected to build continuously suc h currents. We conclude that magnetic reconnection occurs periodically, in the current layer created between the emerging bipoles and the large scale active region field. It induced the observed recurrent coron al jets and the decrease of the vertical electric current mag nitude.

Measuring the Impact of Minimum Wages: Evidence from Latin America

Abstract: This paper first provides an overview of the levels of minimum wages in Latin America and their true impact on the distribution of wages using both numerical measures and kernel density plots. It identifies numeraire' effects higher in the wage distribution and lighthouse' or reference effects in the unregulated or informal' sector. The final section then employs panel employment data from Colombia, a country where minimum wages seem high and very binding, to quantify the effects of an increase on wages and employment. The evidence suggests that in the Latin American context, the minimum wage has impacts beyond those usually contemplated in the advanced country literature.

Expression of α2-macroglobulin receptor/low density lipoprotein receptor-related protein (LRP) in rat microglial cells

Abstract: Low density lipoprotein receptor-related protein (LRP) participates in the uptake and degradation of several ligands implicated in neuronal pathophysiology including apolipoprotein E (apoE), activated a2 -macroglobulin (a2M*) and b-amyloid precursor protein (APP). The receptor is expressed in a variety of tissues. In the brain LRP is present in pyramidal-type neurons in cortical and hippocampal regions and in astrocytes that are activated as a result of injury or neoplasmic transformation. As LRP is expressed in the monocyte/macrophage cell system, we were interested in examining whether LRP is expressed in microglia. We isolated glial cells from the brain of neonatal rats and LRP was immunodetected both in microglial cells and in astrocytes expressing glial fibrillar acidic protein (GFAP). Microglial cells were able to bind and internalize LRP-specific ligand, a2M*. The internalization was inhibitable by RAP, with a Kd of 1.7 nM. The expression of LRP was upregulated by dexamethasone, and down-regulated by lipopolysaccharide (LPS), gamma interferon (IFN-g )o r ac ombination of both. LRP was less sensitive to dexamethasone in activated astrocytes than in microglia. We provided the first analysis of LRP expression and regulation in microglia. Our results open the possibility that microglial cells could be related to the participation of LRP and its ligands in different pathophysiological states in brain. J. Neurosci. Res. 60:401‐411, 2000. © 2000 Wiley-Liss, Inc.

Transforming Governance In Telecoupled Food Systems

Abstract: In this paper we analyze how new actors, interests, and resources become salient to food system governance and how the domain of food system governance transforms as a result. Specifically, we focus on how the boundaries of food systems are redefined and new institutions are developed through the explicit recognition of distal interactions and feedbacks—telecoupling—operating in the food system space. Telecoupling can stimulate new forms of governance, such as the development of codes of conduct and certification schemes, with positive impacts on food and livelihood security; when ignored, telecouplings can exacerbate undesirable social and ecological outcomes in linked systems. We present a typology of telecoupled food systems, highlighting three dimensions of distance that can be present in systems that become telecoupled: social, institutional, and physical. We use that typology to explore the evolution of telecoupling and governance change in two case studies. We associate the tendency for changes in governance that occur in each case with the nature of “distance” in the systems in question: whether the systems are distal in terms of social and/or institutional ties, or in the resource base, or some combination of all three dimensions of distance. The challenge of overcoming distance is not the only issue that affects the possibility of governance change; the cases illustrate that the cultural and economic conditions of the connected systems, the agency of actors involved, and their political and social relations and networks all come to play in enabling governance transformation in telecoupled systems.