Mechanical response of a self avoiding membrane: fold collisions and the birth of conical singularities

An elastic membrane that is forced to reside in a container smaller than its natural size will deform and, upon further volume reduction, eventually crumple. The crumpled state is characterized by the localization of energy in a complex network of highly deformed crescent-like regions joined by line ridges. Previous studies have focused on the onset of the crumpled state by analyzing the mechanical response and stability of a conical dislocation, while others have simulated the highly packed regime neglecting the importance of the connectivity of the membrane. Here we show, through a combination of experiments, numerical simulations, and analytic approach, that the emergence of new regions of high stretching is a generic outcome when a self avoiding membrane is subject to a severe geometrical constraint. We demonstrate that, at moderate packing fraction, interlayer interactions produce a response equivalent to the one of a thicker membrane that has the shape of the deformed one. Evidence is found that friction plays a key role stabilizing the folded structures.Comment: 10 page

On angled bounce-off impact of a drop impinging on a flowing soap film

Small drops impinging angularly on thin flowing soap films frequently demonstrate the rare emergence of bulk elastic effects working in-tandem with the more common-place hydrodynamic interactions. Three collision regimes are observable: (a) drop piercing through the film, (b) it coalescing with the flow, and (c) it bouncing off the film surface. During impact, the drop deforms along with a bulk elastic deformation of the film. For impacts that are close-to-tangential, the bounce-off regime predominates. We outline a reduced order analytical framework assuming a deformable drop and a deformable three-dimensional film, and the idealization invokes a phase-based parametric study. Angular inclination of the film and the ratio of post and pre impact drop sizes entail the phase parameters. We also perform experiments with vertically descending droplets impacting against an inclined soap film, flowing under constant pressure head. Model predicted phase domain for bounce-off compares well to our experimental findings. Additionally, the experiments exhibit momentum transfer to the film in the form of shed vortex dipole, along with propagation of free surface waves. On consulting prior published work, we note that for locomotion of water-walking insects using an impulsive action, the momentum distribution to the shed vortices and waves are both significant, taking up respectively 2/3-rd and 1/3-rd of the imparted streamwise momentum. In view of the potentially similar impulse actions, this theory is applied to the bounce-off examples in our experiments, and the resultant shed vortex dipole momenta are compared to the momenta computed from particle imaging velocimetry data. The magnitudes reveal identical order ($10^{-7}$ N$\cdot$s), suggesting that the bounce-off regime can be tapped as a simple analogue for interfacial bio-locomotion relying on impulse reactions

Macroscopic magnetic frustration

Although geometrical frustration transcends scale, it has primarily been evoked in the micro and mesoscopic realm to characterize such phases as spin-ice liquids and glasses and to explain the behavior of such materials as multiferroics, high temperature superconductors, colloids and copolymers. Here we introduce a system of macroscopic ferromagnetic rotors arranged in a planar lattice capable of out-of-plane movement that exhibit the characteristic honeycomb spin ice rules studied and seen so far only in its mesoscopic manifestation. We find that a polarized initial state of this system settles into the honeycomb spin ice phase with relaxation on multiple time scales. We explain this relaxation process using a minimal classical mechanical model which includes Coulombic interactions between magnetic charges located at the ends of the magnets and viscous dissipation at the hinges. Our study shows how macroscopic frustration arises in a purely classical setting that is amenable to experiment, easy manipulation, theory and computation, and shows phenomena that are not visible in their microscopic counterparts

Intrinsic chiral field as vector potential of the magnetic current in the zig-zag lattice of magnetic dipoles

Chiral magnetic insulators manifest novel phases of matter where the sense of rotation of the magnetization is associated with exotic transport phenomena. Effective control of such phases and their dynamical evolution points to the search and study of chiral fields like the Dzyaloshinskii-Moriya interaction. Here we combine experiments, numerics, and theory to study a zig-zag dipolar lattice as a model of an interface between magnetic in-plane layers with perpendicular magnetization. The zig-zag lattice comprises two parallel sublattices of dipoles with perpendicular easy plane of rotation. The dipolar energy of the system is exactly separable into a sum of symmetric and antisymmetric long-range exchange interactions between dipoles, where the antisymmetric coupling generates a nonlocal Dzyaloshinskii-Moriya field which stabilizes winding textures with the form of chiral solitons. The Dzyaloshinskii-Moriya interaction acts as a vector potential or gauge field of the magnetic current and gives rise to emergent magnetic and electric fields that allow the manifestation of the magnetoelectric effect in the system.Comment: 10 pages, 4 figure

Evaluación económica de proyectos de inversión basada en la teoría de opciones reales

En la presente investigación se analiza un nuevo enfoque, basado en la aplicación de la Teoría de Opciones Reales para realizar la evaluación económica de proyectos de inversión. El mismo, posee el potencial de entregar una aproximación del valor de la flexibilidad que posee un proyecto, permitiendo al evaluador capturar numéricamente el valor de la estrategia.El objetivo fundamental de la presente investigación fue proponer una “Metodología de Evaluación Económica de proyectos de inversión a partir de la Teoría de Opciones Reales”, con el fin de presentarla como una herramienta de evaluación alternativa a los métodos tradicionales. A modo de aplicación de esta metodología, basada en el Método Binomial con Transformada Logarítmica, se realizó la evaluación económica de distintos proyectos reales los cuales corresponden a distintas variaciones del proyecto “Implementación de un Sistema de Información Geográfica (SIG) para controlar la cartografía de las plantaciones pertenecientes a Forestal Mininco S.A” estudiadas previamente por Julio Becker.

Precios internacionales del arroz un analisis de series de tiempo

141 p.La volatilidad asociada a los precios internacionales de los productos agrícolas asociada a factores climáticos y económicos, y su vinculación con los mercados domésticos como referencia en la determinación del precio en dichos mercados. Genera incertidumbre al momento de tomar decisiones de producción y comercialización. Es por esto que el objetivo del presente fue pronosticar los precios internacionales del arroz elaborado 5%, 10% y 15% grano partido FOB Bangkok, Tailandia para el periodo 2009/2011. Se usaron datos mensuales de los precios de cada tipo de arroz, del periodo Octubre de 1992 a Septiembre de 2009. Los valores fueron expresados en moneda de Septiembre de 2009 usando como deflactor el Wholesale Price Index de EE.UU. (WPI). Para analizar las series se utilizó el modelo multiplicativo de integración, con el que se pudo determinar las componentes de Estacionalidad, Tendencia, Ciclo e Irregularidad. Se utilizó el método de promedio geométrico móvil para estimar patrones de estacionalidad ajustada de los precios internacionales del arroz. Estos resultados mostraron: a) cierta estabilidad de precios de Mayo a Agosto y en Diciembre para el arroz elaborado con 5% grano partido, y en Octubre y Diciembre para el arroz elaborado con 10% y 15% grano partido. Como medida de volatilidad se utilizó la desviación estándar de los retornos (variaciones de precios) continuos de cada serie. Para ello fue necesario comprobar la estacionariedad de las series mediante análisis grafico, análisis de correlogramas, test de Durbin Watson, las pruebas de Dickey Fuller, Phillip Perron y Kwiatkowski, Phillips, Schmidt y Shin. Además, se analizó la estabilidad estructural par las diferentes series de precios del arroz elaborado. Estos análisis se realizaron con el apoyo del Software E-views 5.0. Al realizar las pruebas para determinar la estacionariedad de las series, se observó que la serie de precios reales de cada tipo de arroz era no estacionaria; por lo que se transformó a una serie sin tendencia y con media y varianza constante a través del tiempo. Comprobada la estacionariedad de la serie transformada, se utilizó el Software @Risk 5.5 para determinar la mejor distribución de probabilidad para las series transforma; para luego obtener un pronóstico de precios para el arroz elaborado 5%, 10% y 15% grano partido. Estos resultados mostraron que, para el periodo 2009/2011, el arroz con 5% grano partido, presentará una tendencia al alza, al igual que el arroz con 15% grano partido. Sin embargo, el arroz con 10% grano partido presenta una estabilidad en el precio entorno a US$/Kg 0.52 para tener un leve decaimiento en Octubre de 2011. Palabras clave: componentes de series de tiempo, índice de estacionalidad ajustada, estacionariedad, pronóstico

Gastric perforation associated with the intake of ice cream with liquid nitrogen

1 ArtículoLa ingestión de nitrógeno líquido es una causa infrecuente de perforación gástrica, se conoce poco sobre como este compuesto afecta el tejido gastrointestinal, sus mecanismos de lesión y sus consecuencias clínicas. Cada vez es más frecuente el uso del nitrógeno líquido de forma comercial en productos de repostería y gastronomía, por lo que es importante reconocer sus potenciales efectos cuando la manipulación no es la adecuada. En este caso clínico describimos una perforación gástrica secundaria al consumo de helado preparado con nitrógeno líquido

Ovine Fetal Immune Response to Cache Valley Virus Infection

Cache Valley virus (CVV)-induced malformations have been previously reproduced in ovine fetuses. To evaluate the development of the antiviral response by the early, infected fetus, before the development of immunocompetency, ovine fetuses at 35 days of gestation were inoculated in utero with CVV and euthanized at 7, 10, 14, 21, and 28 days postinfection. The antiviral immune response in immature fetuses infected with CVV was evaluated. Gene expression associated with an innate, immune response was quantified by real-time quantitative PCR. The upregulated genes in infected fetuses included ISG15, Mx1, Mx2, IL-1, IL-6, TNF-α, TLR-7, and TLR-8. The amount of Mx1 protein, an interferon-stimulated GTPase capable of restricting growth of bunyaviruses, was elevated in the allantoic and amniotic fluid in infected fetuses. ISG15 protein expression was significantly increased in target tissues of infected animals. B lymphocytes and immunoglobulin-positive cells were detected in lymphoid tissues and in the meninges of infected animals. These results demonstrated that the infected ovine fetus is able to initiate an innate and adaptive immune response much earlier than previously known, which presumably contributes to viral clearance in infected animals

Identification of the Target Cells and Sequence of Infection during Experimental Infection of Ovine Fetuses with Cache Valley Virus

Cache Valley virus-induced malformations have been previously reproduced in ovine fetuses; however, no studies have established the course of infection of cells and tissues with Cache Valley virus. To address these questions, ovine fetuses at 35 days of gestation were inoculated in utero with Cache Valley virus and euthanized at 7, 10, 14, 21, and 28 days postinfection. On postmortem examination, arthrogryposis and oligohydramnios were observed in some infected fetuses. Morphological studies showed necrosis in the central nervous system and skeletal muscle of infected fetuses evaluated after 7 to 14 days postinfection, and hydrocephalus, micromyelia, and muscular loss were observed in infected fetuses after 21 to 28 days postinfection. Using immunohistochemistry and in situ hybridization, intense Cache Valley virus antigen and RNA staining was detected in the brain, spinal cord, skeletal muscle, and, to a lesser degree, in fetal membranes and other tissues of infected fetuses. Viral antigen and RNA staining decreased in targeted and infected tissues with the progression of the infection