Testing for stock market integration in a developing economy: Colombia

This paper examines the linkage between two parallel stock exchanges trading the same shares in Colombia, namely the Bogotá Stock Exchange and the Medellín Stock Exchange. We provide empirical evidence to support the hypothesis that these two markets can be best described as fully integrated over a period of almost four decades, which is consistent with the view that arbitrage opportunities are only possible in the short but not in the long run. In addition, we find evidence that the location of a company´s headquarters appears to matter in stock price formation.Stock market, cointegration, arbitrage, Colombia

A mathematically assisted reconstruction of the initial focus of the yellow fever outbreak in Buenos Aires (1871)

We discuss the historic mortality record corresponding to the initial focus of the yellow fever epidemic outbreak registered in Buenos Aires during the year 1871 as compared to simulations of a stochastic population dynamics model. This model incorporates the biology of the urban vector of yellow fever, the mosquito Aedes aegypti, the stages of the disease in the human being as well as the spatial extension of the epidemic outbreak. After introducing the historical context and the restrictions it puts on initial conditions and ecological parameters, we discuss the general features of the simulation and the dependence on initial conditions and available sites for breeding the vector. We discuss the sensitivity, to the free parameters, of statistical estimators such as: final death toll, day of the year when the outbreak reached half the total mortality and the normalized daily mortality, showing some striking regularities. The model is precise and accurate enough to discuss the truthfulness of the presently accepted historic discussions of the epidemic causes, showing that there are more likely scenarios for the historic facts.Comment: 25 pages, 12 figure

Sobre la lógica en el siglo XIX y su reconstrucción historiográfica

Pretender cubrir en una exposición el conjunto del desarrollo de la lógica en el siglo XIX resulta impensable, entre otras razones por la multitud de trabajos que han aparecido en los últimos años sobre aspectos puntuales y sobre periodos definidos del mismo. Más aún, algunas presentaciones globales que sólo intentan ser, por su misma naturaleza, esquemáticas o aún bibliográficas, contienen o aluden a tal riqueza que confirman lo difícilmente abarcable del lapso referido. No es tampoco necesario recordar la fertilidad y amplitud, perfectible como es obvio, de los trabajos monográficos sobre los aportes principales de Boole, Frege, Peana, quienes son reconocidos alternativamente como los fundadores de la lógica nuestra

Medoid-based clustering using ant colony optimization

The application of ACO-based algorithms in data mining has been growing over the last few years, and several supervised and unsupervised learning algorithms have been developed using this bio-inspired approach. Most recent works about unsupervised learning have focused on clustering, showing the potential of ACO-based techniques. However, there are still clustering areas that are almost unexplored using these techniques, such as medoid-based clustering. Medoid-based clustering methods are helpful—compared to classical centroid-based techniques—when centroids cannot be easily defined. This paper proposes two medoid-based ACO clustering algorithms, where the only information needed is the distance between data: one algorithm that uses an ACO procedure to determine an optimal medoid set (METACOC algorithm) and another algorithm that uses an automatic selection of the number of clusters (METACOC-K algorithm). The proposed algorithms are compared against classical clustering approaches using synthetic and real-world datasets

Extending the SACOC algorithm through the Nystrom method for dense manifold data analysis

Data analysis has become an important field over the last decades. The growing amount of data demands new analytical methodologies in order to extract relevant knowledge. Clustering is one of the most competitive techniques in this context.Using a dataset as a starting point, these techniques aim to blindly group the data by similarity. Among the different areas, manifold identification is currently gaining importance. Spectral-based methods, which are the mostly used methodologies in this area, are however sensitive to metric parameters and noise. In order to solve these problems, new bio-inspired techniques have been combined with different heuristics to perform the clustering solutions and stability, specially for dense datasets. Ant Colony Optimization (ACO) is one of these new bio-inspired methodologies. This paper presents an extension of a previous algorithm named Spectral-based ACO Clustering (SACOC). SACOC is a spectral-based clustering methodology used for manifold identification. This work is focused on improving this algorithm through the Nystrom extension. The new algorithm, named SACON, is able to deal with Dense Data problems.We have evaluated the performance of this new approach comparing it with online clustering algorithms and the Nystrom extension of the Spectral Clustering algorithm using several datasets

Choline Supplementation and Dna Methylation in the Hippocampus and Prefrontal Cortex of Rats Exposed to Alcohol During Development

Fetal Alcohol Spectrum Disorders (FASD) refers to the effects of alcohol exposure during development on individuals. Some of the most frequent deficits seen in children with FASD and in animal models of FASD are spatial memory impairments and impaired executive functioning, which are likely related to alcohol-induced alterations of the hippocampus and medial prefrontal cortex (mPFC), respectively. Choline, a nutrient supplement, has been shown in a rat model to ameliorate some of alcohol‟s teratogenic effects and this effect may be mediated through choline‟ effects on DNA methylation. This study used a rat model of FASD to investigate the underlying mechanisms of alcohol-induced deficits and the impact of choline on these deficits by examining changes in DNA methylation in the PFC and hippocampal areas. Alcohol was given by intragastric intubation to rat pups during the neonatal period (postnatal days 2-10) (ET group), which is equivalent to the third trimester in humans and a period of heightened vulnerability of the brain to alcohol exposure. Control groups included an intubated control group given the intubation procedure without alcohol (IC) and a non-treated control group (NC). Choline or saline was administered subcutaneously to each subject from postnatal day 2 to 20. On postnatal day 21, the brains of the subjects were removed and processed for relative optical density (ROD) of immunohistochemical staining for neuronal-specific enolase (NSE) and global DNA methylation as measured by chemiluminescence using the cpGlobal assay. In the mPFC, choline supplementation led to significant increases in ROD of staining for NSE, regardless of treatment or sex. No differences in NSE staining were found in the CA1 region of the hippocampus. Alcohol exposure caused hypermethylation in the hippocampus and mPFC, which was significantly reduced after choline supplementation. In contrast, control animals showed increases in DNA methylation in both regions after choline supplementation, suggesting that choline supplementation has different effects depending upon the initial state of the brain. This study is the first to show in a rat model of FASD changes in global DNA methylation of the hippocampus CA1 region and mPFC after neonatal alcohol exposure with and without choline supplementation. Molecular mechanisms of alcohol‟s teratogenesis leading to a state of hypermethylation are proposed based on alcohol‟s and choline‟s effects in the folate/choline path to DNA methylation

Géneros sin límites en Hugo Wenceslao Amable

La obra del escritor Hugo Wenceslao Amable está determinada por la confluencia de diversos géneros discursivos cuyos límites atraviesan aquellas disciplinas -como la lingüística, la literatura y el periodismo- correspondientes al campo intelectual de producción. La contaminación genérica sin pertenencia hace que la producción de este autor tenga un tinte destacad

Forecasting inflation under varying frequencies

This paper seeks to determine the impact of monthly and annual data frequencies on the accuracy of inflation forecasts attainable via econometric and subspace-based methods. The application considers food inflation across short and long run horizons in Colombia, a country with an inflation targeting regime. The data includes all 54 components of the food consumer price index (CPI) in Colombia from Jan. 1999 Oct. 2012, and the study forecasts the food CPI, and inflation using the parametric and nonparametric techniques of ARIMA, Exponential Smoothing (ETS), Holt-Winters (HW) and Singular Spectrum Analysis (SSA). We �nd that when forecasting the index, ARIMA forecasts are on average best, whilst for monthly inflation forecasting SSA is comparatively better and for annual, the results vary between SSA and ARIMA. These statistically signi�cant �ndings give policy makers an option to select an apt forecasting model which suits their requirements

Time-stepping approach for solving upper-bound problems: Application to two-dimensional Rayleigh-Benard convection

An alternative computational procedure for numerically solving a class of variational problems arising from rigorous upper-bound analysis of forced-dissipative infinite-dimensional nonlinear dynamical systems, including the Navier-Stokes and Oberbeck-Boussinesq equations, is analyzed and applied to Rayleigh-Benard convection. A proof that the only steady state to which this numerical algorithm can converge is the required global optimal of the relevant variational problem is given for three canonical flow configurations. In contrast with most other numerical schemes for computing the optimal bounds on transported quantities (e.g., heat or momentum) within the "background field" variational framework, which employ variants of Newton's method and hence require very accurate initial iterates, the new computational method is easy to implement and, crucially, does not require numerical continuation. The algorithm is used to determine the optimal background-method bound on the heat transport enhancement factor, i.e., the Nusselt number (Nu), as a function of the Rayleigh number (Ra), Prandtl number (Pr), and domain aspect ratio L in two-dimensional Rayleigh-Benard convection between stress-free isothermal boundaries (Rayleigh's original 1916 model of convection). The result of the computation is significant because analyses, laboratory experiments, and numerical simulations have suggested a range of exponents alpha and beta in the presumed Nu similar to (PrRa beta)-Ra-alpha scaling relation. The computations clearly show that for Ra <= 10(10) at fixed L = 2 root 2, Nu <= 0.106Pr(0)Ra(5/12), which indicates that molecular transport cannot generally be neglected in the "ultimate" high-Ra regime.NSF DMS-0928098 DMS-1515161 DMS-0927587 PHY-1205219Simons FoundationNSFONRInstitute for Computational Engineering and Sciences (ICES

The Angiotensin Affair: How Great Minds Thinking Alike Came to a Historical Agreement

In 1934, J. C. Fasciolo had to submit a thesis and Dr. Houssay suggested he investigate about nephrogenic hypertension. E. Braun‐Menéndez showed interest in helping and Drs. L.F. Leloir and J.M. Muñoz from the Institute of Physiology joined them in their attempt to isolate and purify the pressor substance. In 1939, they extracted the substance “hypertension” from the venous blood from the ischemic kidneys. They proposed an enzyme‐substrate reaction. They named hypertensinogen the substrate and hypertensinases the enzymes that break down the hypertension. Two months following the Argentine publication, the team in the United States, formed by I.H. Page and O.M. Helmer, published their findings, which were in agreement with those reported by the Argentine team. By 1940, they isolated angiotonin, the equivalent of hypertension, and called the renin substrate hypertensinogen. In 1957, in the conference held in Ann Arbor, Braun‐Menéndez and Page agreed on a new nomenclature. As a result, the words angiotensinogen and angiotensin were born from the combination of the names originally set by both teams. The discovery of the renin‐angiotensin system is an example that science should follow: Value the progress made by colleagues, collaborate side by side, and pursue the ultimate truth