Comments on the U(2) noncommutative instanton

We discuss the 't Hoof ansatz for instanton solutions in noncommutative U(2) Yang-Mills theory. We show that the extension of the ansatz leading to singular solutions in the commutative case, yields to non self-dual (or self-antidual) configurations in noncommutative space-time. A proposal leading to selfdual solutions with Q=1 topological charge (the equivalent of the regular BPST ansatz) can be engineered, but in that case the gauge field and the curvature are not Hermitian (although the resulting Lagrangian is real).Facultad de Ciencias Exacta

Interpolating Boundary Conditions on AdS2AdS_2

We consider two instances of boundary conditions for massless scalars on $AdS_2$ that interpolate between the Dirichlet and Neumann cases while preserving scale invariance. Assessing invariance under the full SL(2;\mathds{R}) conformal group is not immediate given their non-local nature. To further clarify this issue, we compute holographically 2- and 4-point correlation functions using the aforementioned boundary conditions and study their transformation properties. Concretely, motivated by the dual description of some multi-parametric families of Wilson loops in ABJM theory, we look at the excitations of an open string around an $AdS_2\subset AdS_4\times\mathbb{CP}^3$ worldsheet, thus obtaining correlators of operators inserted along a $1$-dimensional defect in ${\cal N}=6$ super Chern-Simons-matter theory at strong coupling. Of the two types of boundary conditions analyzed, only one leads to the expected functional structure for conformal primaries; the other exhibits covariance under translations and rescalings but not under special conformal transformations

Regeneración de palmas en bosques nativos y plantaciones del Santuario de Fauna y Flora Otún - Quimbaya (Risaralda, Colombia)

Because of their structural, functional and ecological importance, palms are a key group in understanding the processes of regeneration in Neotropical montane forests. We studied the regeneration of palms in the Fauna and Flora Otún-Quimbaya Sanctuary along five transects of 50x4 m (0,1 ha) in five forest types: mature native forest (MNF), secondary forest (SF), pine plantation (Pinus patula) (PP), oak plantation (Quercus humboldtii) (OP), and Chinese ash plantation (Fraxinus chinensis) (AP). We recorded all individuals of each species, including seedlings, juveniles and adults, taking as variables the diversity, frequency of occurrence and population structure by forest type. Species richness (ten species) was high compared with other studies conducted in similar mountain forests. The most abundant species was Geonoma undata, with nearly half of all individuals recorded, followed by Prestoea acuminata Chamaedorea pinnatifrons Ceroxylon alpinum Wettinia kalbreyeri Chamaedorea linearis Geonoma jussieuana Aiphanes simplex Geonoma orbignyana and Aiphanes lindeniana. The MNF had the highest diversity (Shannon index H' = 1,83, Simpson's Reciprocal index 1/D = 5,43), followed by the SF, PP, OP and AP. The MNF also presented the highest richness (ten species), followed by the SF, AP, PP and OP. The high diversity and richness of palms in the MNF is associated with a longer recruitment time and persistence of species, as well as with the higher structural and functional heterogeneity. The low diversity and richness of the plantations are associated with the lower structural and functional heterogeneity, and the edaphic restrictions in the OP and PP. The presence of individuals of G. undata C. alpinum and Ch. pinnatifrons in all types of forests, with the highest frequency of occurrence by total transects (fr = 0,88, 0,72 and 0,72 respectively), indicates that these species have a high potential to colonize different environments. The AP has the best conditions for the germination and recruitment of Ch. linearis G. undata Ch. pinnatifrons and C. alpinum, as evidenced by the higher percentage of seedlings and juveniles found among forest types (70,2%, 69%, 49,8% and 37,1% respectively), which is probably related to a low light variance and/or increased light availability, as well as abundant litter. Because the MNF has all palm species, with the highest percentage of adults per species, this type of forest is critical for seed production and palm regeneration in the Sanctuary

Dried fruit breadfruit slices by Refractive Window™ technique

Una gran cantidad de productos son secados por diversas razones, tales como la preservación, la reducción de peso y el mejoramiento de su estabilidad. Sin embargo, los métodos tradicionales de secado de alimentos sólidos no presentan productos de bajo costo y alta calidad de manera simultánea. A pesar de que existen métodos efectivos de deshidratación de los alimentos como la liofilización, que preserva el sabor, color y las vitaminas, son tecnologías de poca accesibilidad, por lo cual se hacen necesarios procesos alternativos que sean eficientes y económicos. El objetivo de esta investigación fue comparar la cinética del secado de rebanadas de fruto del árbol del pan (Artocarpus communis) mediante la técnica de Ventana Refractiva® (VR) con la de secado en bandeja. Para llegar a cabo este trabajo, se usaron rodajas de 1 y 2 mm de espesor. El secado con VR se realizó con temperatura del baño de agua a 92 °C; y el secado en bandeja a 62 °C y una velocidad del aire de 0,52 m/s. Durante el secado por la técnica de VR, el contenido de humedad llega a niveles más bajos que el secado en bandejas. De igual manera sucede con las muestras de 1 mm, las cuales, por tener menor diámetro alcanzan niveles de humedad inferior que las muestras de 2 mm. Las mayores difusividades se obtuvieron durante el secado por VR en rodajas de 1 y 2 mm con coeficientes de 6,13 y 3,90*10-9 m2/s respectivamente.A large amount of products are dried due several reasons as preservation, weight reduction and improvement of stability. However, on the market are not offered low-cost and high quality products simultaneously. Although there are effective methods of dehydrating foods such as freeze drying, which preserves the flavor, color and vitamins, they are poor accessibility technologies. Therefore, alternative processes are required to be efficient and economical. The aim of this research was compare drying kinetics of sliced of breadfruit (Artocarpus communis) using the technique of Refractive Window® (VR) with the tray drying. To carry out this study, sliced of 1 and 2 mm thick were used. Refractive window drying was performed with the water bath temperature to 92 °C; and tray drying at 62 °C and an air velocity of 0.52 m/s. During the Refractive window drying technique, the moisture content reached the lower than tray drying levels. Similarly it happened with samples of 1 mm, which, having a smaller diameter reached lower moisture levels than samples 2 mm. The higher diffusivities were obtained during drying sliced VR 1 and 2 mm with coefficients of 6.13 and 3.90*10-9 m2/s respectively

Strings in bubbling geometries and dual Wilson loop correlators

We consider a fundamental string in a bubbling geometry of arbitrary genus dual to a half-supersymmetric Wilson loop in a general large representation R of the SU(N) gauge group in N= 4 Supersymmetric Yang-Mills. We demonstrate, under some mild conditions, that the minimum value of the string classical action for a bubbling geometry of arbitrary genus precisely matches the correlator of a Wilson loop in the fundamental representation and one in a general large representation. We work out the case in which the large representation is given by a rectangular Young tableau, corresponding to a genus one bubbling geometry, explicitly. We also present explicit results in the field theory for a correlator of two Wilson loops: a large one in an arbitrary representation and a “small” one in the fundamental, totally symmetric or totally antisymmetric representation.Instituto de Física La Plat

Strings in bubbling geometries and dual wilson loop correlators

We consider a fundamental string in a bubbling geometry of arbitrary genus dual to a half-supersymmetric Wilson loop in a general large representation R of the SU(N) gauge group in N = 4 Supersymmetric Yang-Mills. We demonstrate, under some mild conditions, that the minimum value of the string classical action for a bubbling geometry of arbitrary genus precisely matches the correlator of a Wilson loop in the fundamental representation and one in a general large representation. We work out the case in which the large representation is given by a rectangular Young tableau, corresponding to a genus one bubbling geometry, explicitly. We also present explicit results in the field theory for a correlator of two Wilson loops: a large one in an arbitrary representation and a “small” one in the fundamental, totally symmetric or totally antisymmetric representation.Facultad de Ciencias Exacta

Cientópolis: motorizando la ciencia ciudadana

En ciertas situaciones como la toma, clasificación y etiquetado de muestras, el científico realiza un gran número de tareas simples, repetitivas, que no pueden ser automatizadas y que podrían ser ejecutadas por personas sin formación en la materia si se las entrena y asiste con herramientas. En el pasado, en proyectos de conservación, astronomía y biología, entre otros, este tipo de tareas se ha delegado de manera efectiva a voluntarios. Cuando se convoca a ciudadanos voluntarios para colaborar con los científicos, se habla de ciencia ciudadana. Encontrar e involucrar a esos voluntarios, sumado a coordinar y reconocer su trabajo, es una tarea compleja. Definir y conducir proyectos de ciencia ciudadana presenta desafíos en tres áreas críticas: metodologías, tecnologías y construcción de comunidades de voluntarios. El proyecto Cientópolis (http://cientopolis.org) tiene como objetivo producir avances en estas tres áreas y socializarlos con la comunidad. En la actualidad, Cientópolis brinda espacios para compartir conocimiento y experiencias, ofrece herramientas para la construcción de proyectos de toma de muestras con dispositivos móviles y construcción colaborativa de conocimiento, da acceso a una comunidad creciente de ciudadanos científicos y explora estrategias de ludificación para consolidar y sostener dicha comunidad.Trabajo presentado por el Laboratorio de Investigación y Formación en Informática Avanzada (LIFIA

Técnicas de control adaptativas aplicadas a sistemas multivariables (m.i.m.o.)

En este artículo muestra un control PID y por Reubicación de Polos que son implementados adaptativamente, mediante la incorporación de variantes para que el sistema pueda ser manejado desde un computador digital por medio de la adquisición de datos. Se simula el control multivariable de frecuencia y voltaje de un generador sincrónico real de 1/3 Hp, 120 V, 1800 RPM y 4 polos. Sus parámetros fueron identificados previamente de manera adaptativa partiendo de un modelomatemático de tercer orden (esquema de identificación fuera de línea). Los resultados obtenidos muestran la eficacia de ambas estructuras de control

On the Mechanism of the Copper-Catalyzed Enantioselective 1,4-Addition of Grignard Reagents to α,β-Unsaturated Carbonyl Compounds

The mechanism of the enantioselective 1,4-addition of Grignard reagents to α,β-unsaturated carbonyl compounds promoted by copper complexes of chiral ferrocenyl diphosphines is explored through kinetic, spectroscopic, and electrochemical analysis. On the basis of these studies, a structure of the active catalyst is proposed. The roles of the solvent, copper halide, and the Grignard reagent have been examined. Kinetic studies support a reductive elimination as the rate-limiting step in which the chiral catalyst, the substrate, and the Grignard reagent are involved. The thermodynamic activation parameters were determined from the temperature dependence of the reaction rate. The putative active species and the catalytic cycle of the reaction are discussed.