Reduced dynamics and Lagrangian submanifolds of symplectic manifolds

In this paper, we will see that the symplectic creed by Weinstein "everything is a Lagrangian submanifold" also holds for Hamilton-Poincar\'e and Lagrange-Poincar\'e reduction. In fact, we show that solutions of the Hamilton-Poincar\'e equations and of the Lagrange-Poincar\'e equations are in one-to-one correspondence with distinguished curves in a Lagrangian submanifold of a symplectic manifold. For this purpose, we will combine the concept of a Tulczyjew triple with Marsden-Weinstein symplectic reduction.Comment: 26 page

Interconexión eléctrica Colombia-Panamá: impacto sobre el precio spot en Panamá.

El objetivo de este paper es analizar el impacto que tendría la integración energética prevista entre Colombia y Panamá sobre el precio spot en Panamá. Por medio de un modelo de Vectores de Corrección del Error (VEC) con datos mensuales entre 2000 y 2011 y un análisis impulso-respuesta del comportamiento del precio Spot ante choques de importaciones e incrementos de costos de combustibles de las centrales térmicas en Panamá y exportaciones desde Colombia y un pronóstico del precio Spot entre enero y julio de 2012; los principales resultados muestran que por medio de esta interconexión, Colombia tendría un impacto importante en la reducción del precio de energía Ocasional de Panamá. Esto es, por un aumento de un 1% en las exportaciones de energía de Colombia el precio spot en panamá se reduciría el 12%

Crédito, Exceso de toma de Riesgo, Costo de Crédito y ciclo Económico en Chile

This paper studies the interaction between the business cycle and the credit market. A first result is that the business cycle has procyclical effects on different types of credit (i.e., consumer, commercial and mortgage loans). The results area obtained through the identification of structural shocks of VAR models that empirically replicate the standard transmission mechanism of monetary policy that has been found in previous work on the Chilean economy. However, our evidence points to new results. Periods of economic expansion trigger in the medium term, first, an increase in non– performing loans, and then, a decline in credit. We interpret this phenomenon as excessive risktaking. Similarly, periods of economic contraction and high interest rates are followed by a drop in non–performing loans in the medium term and then by a credit expansion. Finally, unexpected increases in non–performing loans can also produce contractionary effects, a rise in inflation by increasing credit risk and financial costs for firms.

Routh reduction and the class of magnetic Lagrangian systems

In this paper, some new aspects related to Routh reduction of Lagrangian systems with symmetry are discussed. The main result of this paper is the introduction of a new concept of transformation that is applicable to systems obtained after Routh reduction of Lagrangian systems with symmetry, so-called magnetic Lagrangian systems. We use these transformations in order to show that, under suitable conditions, the reduction with respect to a (full) semi-direct product group is equivalent to the reduction with respect to an Abelian normal subgroup. The results in this paper are closely related to the more general theory of Routh reduction by stages.Comment: 23 page

Material-driven fibronectin assembly for high-efficiency presentation of growth factors

Growth factors (GFs) are powerful signaling molecules with the potential to drive regenerative strategies, including bone repair and vascularization. However, GFs are typically delivered in soluble format at supraphysiological doses because of rapid clearance and limited therapeutic impact. These high doses have serious side effects and are expensive. Although it is well established that GF interactions with extracellular matrix proteins such as fibronectin control GF presentation and activity, a translation-ready approach to unlocking GF potential has not been realized. We demonstrate a simple, robust, and controlled material-based approach to enhance the activity of GFs during tissue healing. The underlying mechanism is based on spontaneous fibrillar organization of fibronectin driven by adsorption onto the polymer poly(ethyl acrylate). Fibrillar fibronectin on this polymer, but not a globular conformation obtained on control polymers, promotes synergistic presentation of integrin-binding sites and bound bone morphogenetic protein 2 (BMP-2), which enhances mesenchymal stem cell osteogenesis in vitro and drives full regeneration of a nonhealing bone defect in vivo at low GF concentrations. This simple and translatable technology could unlock the full regenerative potential of GF therapies while improving safety and cost-effectiveness

Fish assemblages in a small temperate estuary on the argentinian coast: spatial variation, environmental influence and relevance as nursery area

The effects of different environmental variables on the fish community structure were evaluated in a small temperate estuary. The biological and environmental data were collected bimonthly between 2007 and 2009 along the main estuarine axis. Multivariate analyses were applied (CLUSTER, SIMPER, CCA) to determine the spatial structure of fish community and to estimate the environmental influence on it. A total of 48 species of “teleost” fishes were observed, with the families Characidae and Sciaenidae presenting the largest number of species, 90% of the catches being juveniles. The fish community was overwhelmingly dominated by one species (Micropogonias furnieri, 88.9%), and only four species contributed more than 1% of total catch (Odontesthes argentinensis 5.4%, Brevoortia aurea 1.1%, Paralonchurus brasiliensis 1.1%, and Mugil platanus 1.0%). Estuarine and freshwater stragglers dominated in number of species, followed by freshwater migrants and marine migrants. Three areas with different fish assemblages, with distinctive species and functional guilds, were defined along the main axis. The occurrence and spatial spread of these areas were linked to spatial variation in salinity, which was consistently influenced by discharge from the Río de la Plata and local precipitation. The results highlight the importance of shallow environments as nursery areas and permit emphasis on their susceptibility to environmental changes.Foram avaliados os efeitos das diferentes variáveis ambientais na estrutura da comunidade de peixes em um pequeno estuário temperado. Dados biológicos e ambientais foram obtidos bimestralmente entre 2007 e 2009, ao longo do eixo principal do estuário. Análises multivariadas foram aplicadas (CLUSTER, SIMPER, CCA) para determinar a estrutura espacial da comunidade de peixes e para estimar a influência ambiental sobre ela. Um total de 48 espécies de "teleósteos" foi observado, com as famílias Characidae e Sciaenidae apresentando o maior número de espécies e sendo 90% das capturas formada por juvenis. A comunidade de peixes foi altamente dominada por uma só espécie (Micropogonias furnieri, 88,9%) e quatro espécies contribuiram com pouco mais de 1% cada para o total das capturas (Odontesthes argentinensis 5,4%, Brevoortia aurea 1,1%, Paralonchurus brasiliensis 1,1% e Mugil platanus 1,0%). Retardatários estuarinos e de água doce dominaram em número de espécies, seguidos por migrantes de água doce e marinhos. Ao longo do eixo principal foram definidas três áreas distintas, cada uma apresentando assembleias de peixes com espécies e guildas funcionais distintas. A ocorrência e abrangência espacial dessas áreas estiveram ligadas à variação espacial na salinidade, que consistentemente foi influenciada pela descarga do Rio da Prata e pela precipitação local. Os resultados destacam a importância dos ambientes rasos como áreas de berçário e permitem enfatizar sua susceptibilidade às mudanças ambientais.Facultad de Ciencias Naturales y Muse

Photodegradation of nimodipine and felodipine in microheterogeneous systems

Indexación: Web of Science; ScieloThe photochemical behavior of nimodipine (NIMO) and felodipine (FELO), photolabile drugs widely used as antihypertensive calcium channel blockers, is studied in constrained media. Specifically, we are interested in the kinetic analysis of 4-aryl-1,4-dihydropyridine photodegradation processes when they are incorporated in biological-mimicking systems like micelles or liposomes. In order to establish if the nature of the head of surfactant (ionic or nonionic) could be important modulating the photo-reactivity of these drugs, we studied the photodegradation of NIMO and FELO incorporated in micelles formed with sodium dodecyl sulfate (SDS, anionic), dodecyl-pyridinium chloride (DPC, cationic) and mono lauryl sucrose ester (MLS, nonionic) as surfactants. Additionally, the results of the photodegradation of these compounds in liposomes were also included. The results clearly indicate that both dihydropyridines studied, NIMO and FELO, are located near to the interface, but the surface charge of micelles does not affect neither, the photodegradation rate constant nor the photodegradation products profile. The absence of singlet oxygen generation in micellar media is consistent with the proposition of these 4-aryl-1,4-dihidropyridines located near to the interface of the micelle, where a polar environment is sensed. In addition, the ethanol preferential location on membranes and dihydropyridine enhanced photodegradation by alcohol presence are interesting results to consider in future research.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072012000300025&nrm=is

A Meiotic Checkpoint Alters Repair Partner Bias to Permit Inter-sister Repair of Persistent DSBs

Accurate meiotic chromosome segregation critically depends on the formation of inter-homolog crossovers initiated by double-strand breaks (DSBs). Inaccuracies in this process can drive aneuploidy and developmental defects, but how meiotic cells are protected from unscheduled DNA breaks remains unexplored. Here we define a checkpoint response to persistent meiotic DSBs in C. elegans that phosphorylates the synaptonemal complex (SC) to switch repair partner from the homolog to the sister chromatid. A key target of this response is the core SC component SYP-1, which is phosphorylated in response to ionizing radiation (IR) or unrepaired meiotic DSBs. Failure to phosphorylate (syp-16A) or dephosphorylate (syp-16D) SYP-1 in response to DNA damage results in chromosome non-dysjunction, hyper-sensitivity to IR-induced DSBs, and synthetic lethality with loss of brc-1BRCA1. Since BRC-1 is required for inter-sister repair, these observations reveal that checkpoint-dependent SYP-1 phosphorylation safeguards the germline against persistent meiotic DSBs by channelling repair to the sister chromatid.Cancer Research UK FC0010048UK Medical Research Council FC0010048Wellcome Trust FC0010048Ministerio de Economía y Competitividad BFU2016-75058-PEuropean Research Council ERC2014 AdG669898 TARLOO

Impacto de la regulación en la eficiencia asignativa del mercado spot eléctrico colombiano

Este paper utilizando un modelo de regresión con estructura ARCH, analiza el efecto de la implementación de algunas medidas regulatorias y de variables fundamentales (relación entre la demanda comercial y la disponibilidad real, El Niño y los aportes hidrológicos) en el Mercado de Energía Mayorista en Colombia sobre el precio spot. Los resultados obtenidos evidencian que las regulaciones establecidas por la Comisión de Regulación de Energía y Gas, han impactado estadística y significativamente el precio spot. Además, El Niño y los aportes hidrológicos presentan un impacto positivo y negativo, respectivamente sobre el precio spot, debido a la gran participación hidráulica de este mercado.This paper uses an ARCH regression model to analyze the effect of several regulatory measures and fundamental factors (the relationship between commercial demand and real availability, El Niño, and water supplies) on the spot price in the Colombian wholesale power market. The results indicate that the regulations established by the Electricity and Gas Regulatory Commission have had a substantial and statistically-significant effect on spot prices. In addition, El Niño and hydro supplies have a positive and negative respectively effect on the spot price, due to the large share of hydropower in this market