Dynamics of conduction blocks in a model of paced cardiac tissue

We study numerically the dynamics of conduction blocks using a detailed electrophysiological model. We find that this dynamics depends critically on the size of the paced region. Small pacing regions lead to stationary conduction blocks while larger pacing regions can lead to conduction blocks that travel periodically towards the pacing region. We show that this size-dependence dynamics can lead to a novel arrhythmogenic mechanism. Furthermore, we show that the essential phenomena can be captured in a much simpler coupled-map model.Comment: 8 pages 6 figure

El impacto de los accidentes de tránsito en el sector salud y la economía familiar. Managua, Enero-Diciembre 1995.

Investigación que analiza el impacto de los accidentes de tránsito sobre los servicios de salud y las repercusiones en la economía familiar. Los resultados indican que los accidentes provocaron gastos directos a las familias de los involucrados, días sin laborar, disminución del ingreso individual, pérdida de la productividad y gastos en los servicios de salud. Además se suma la utilización de los servicios de salud que pudieron emplearse en la atención de otras patologías. Se concluye que hubo un alto grado de impacto de los accidentes en la economía familiar, en la economía del país, en el sector salud ocasionando pérdida de vidas humanas e incrementando la morbilidad

Quantum Games Entropy

We propose the study of quantum games from the point of view of quantum information theory and statistical mechanics. Every game can be described by a density operator, the von Neumann entropy and the quantum replicator dynamics. There exists a strong relationship between game theories, information theories and statistical physics. The density operator and entropy are the bonds between these theories. The analysis we propose is based on the properties of entropy, the amount of information that a player can obtain about his opponent and a maximum or minimum entropy criterion. The natural trend of a physical system is to its maximum entropy state. The minimum entropy state is a characteristic of a manipulated system i.e. externally controlled or imposed. There exist tacit rules inside a system that do not need to be specified or clarified and search the system equilibrium under the collective welfare principle. The other rules are imposed over the system when one or many of its members violate this principle and maximize its individual welfare at the expense of the group.Comment: 6 page

Geological Characterization and Reserve Growth Potential of Spraberry Reservoirs in the Midland Basin, West Texas

Major reservoirs in the Spraberry-Dean play of the Midland Basin, West Texas, initially contained approximately 10.6 billion barrels of oil at discovery. However, current projections indicate that only around 7 percent of this vast resource will be recovered. Despite the significant remaining reserves, a large amount of mobile oil remains trapped in place due to reservoir heterogeneities at abandonment. Consequently, these reservoirs present excellent opportunities for reserve growth through extended conventional recovery methods. Given the substantial volume of movable, nonresidual oil estimated to be present (more than 4 billion barrels), the Spraberry reservoirs were selected for detailed reinvestigation aimed at extended conventional recovery through strategic infield exploration. It was recognized that these reservoirs exhibit significant heterogeneity. Therefore, the primary objective of the project was to determine how an understanding of the genetic stratigraphy of these reservoirs could be leveraged to maximize recovery. Traditionally, Spraberry reservoirs have been perceived as homogeneous "layer cake" oil pools, with development strategies focusing on natural fractures while overlooking the depositional sedimentary architecture of the productive sandstones and siltstones. This reinvestigation seeks to rectify this oversight and explore new approaches to optimize recovery from these complex reservoirs.Bureau of Economic Geolog

Evaluation of Two "in vitro" Digestibility Tests with the "in vivo" Test of Alfalfa (Medicago sativa) in Guinea Pig (Cavia porcellus) Feeding

The purpose of the present study was to compare two types of "in vitro" digestibility assays by using commercial enzymes and guinea pig cecalliquor with the in vivo assay, to identify the assay that most resembles the in vivo response. The alfalfa was used in two cutting times of 30 and 45 days. The "in vivo" digestibility of alfalfa was analyzed, obtaining that after 30 days of cutting the digestibility was 53.64% and at 45 days it was 47.72%, while for the digestibility "in vitro", the DaisyII®-Ankom Technology with cecal liquor and commercial pepsin; for the cecal liquor a value of 55.46% and 49.90% was obtained, for the alfalfa in the two cutting times, while the digestibility with enzymes was 71.01% and 66.34% respectively. It was determined that the method with more relation to the in vivo test corresponds to the trial with cecal liquor, because it presents a lower statistical difference (p <0.05) for both cut-off times. At the same time, it is identified that the protein is the nutrient that has a higher digestibility coefficient, becoming an indicator of the nutritional quality of the food

Horizons: nuclear astrophysics in the 2020s and beyond

Nuclear astrophysics is a field at the intersection of nuclear physics and astrophysics, which seeks to understand the nuclear engines of astronomical objects and the origin of the chemical elements. This white paper summarizes progress and status of the field, the new open questions that have emerged, and the tremendous scientific opportunities that have opened up with major advances in capabilities across an ever growing number of disciplines and subfields that need to be integrated.We take a holistic view of the field discussing the unique challenges and opportunities in nuclear astrophysics in regards to science, diversity, education, and the interdisciplinarity and breadth of the field. Clearly nuclear astrophysics is a dynamic field with a bright future that is entering a new era of discovery opportunities.National Science Foundation (NSF) PHY1430152 OISE-1927130ExtreMeMatter Institute EMMI at the GSI Helmholtzzentrumfur Schwerionenforschung in DarmstadtEuropean Cooperation in Science and Technology (COST) CA1611

Transformation elastodynamics and active exterior acoustic cloaking

This chapter consists of three parts. In the first part we recall the elastodynamic equations under coordinate transformations. The idea is to use coordinate transformations to manipulate waves propagating in an elastic material. Then we study the effect of transformations on a mass-spring network model. The transformed networks can be realized with "torque springs", which are introduced here and are springs with a force proportional to the displacement in a direction other than the direction of the spring terminals. Possible homogenizations of the transformed networks are presented, with potential applications to cloaking. In the second and third parts we present cloaking methods that are based on cancelling an incident field using active devices which are exterior to the cloaked region and that do not generate significant fields far away from the devices. In the second part, the exterior cloaking problem for the Laplace equation is reformulated as the problem of polynomial approximation of analytic functions. An explicit solution is given that allows to cloak larger objects at a fixed distance from the cloaking device, compared to previous explicit solutions. In the third part we consider the active exterior cloaking problem for the Helmholtz equation in 3D. Our method uses the Green's formula and an addition theorem for spherical outgoing waves to design devices that mimic the effect of the single and double layer potentials in Green's formula.Comment: Submitted as a chapter for the volume "Acoustic metamaterials: Negative refraction, imaging, lensing and cloaking", Craster and Guenneau ed., Springe

Enhancement of near-cloaking. Part II: the Helmholtz equation

The aim of this paper is to extend the method of improving cloaking structures in the conductivity to scattering problems. We construct very effective near-cloaking structures for the scattering problem at a fixed frequency. These new structures are, before using the transformation optics, layered structures and are designed so that their first scattering coefficients vanish. Inside the cloaking region, any target has near-zero scattering cross section for a band of frequencies. We analytically show that our new construction significantly enhances the cloaking effect for the Helmholtz equation.Comment: 16pages, 12 fugure

Imágenes en oncología: generalidades y aplicaciones

ResumenLas imágenes tienen un rol fundamental en la oncología actual, que incluye el diagnóstico, etapificación, evaluación de respuesta al tratamiento y diagnóstico de complicaciones. El examen de mayor importancia en estos pacientes es la Tomografía Computada, que tiene un alto rendimiento y resolución espacial, es rápida y disponible en los distintos centros. Otros exámenes son de ayuda complementaria como el Ultrasonido y la Resonancia Magnética. Los estudios metabólicos, y especialmente los de tipo híbrido como el PET/CT, han mejorado la sensibilidad y especificidad en el estudio de diversas neoplasias, tanto en la etapificación, como en el control de tratamiento y seguimiento. En el futuro, con nuevas técnicas, podremos diagnosticar cánceres en una etapa muy precoz, incluso antes de que se manifiesten clínicamente.SummaryImaging has a pivotal role in oncology, including diagnosis, staging, response assessment to therapy and the diagnosis of complications. The most important modality is Computed Tomography, with high accuracy and spatial resolution, fast and not so expensive. Other modalities are Ultrasound and Magnetic Resonance. Metabolic studies such as PET/CT have high accuracy in staging, and follow up of different cancers. In the future, newer techniques will be available in order to diagnose even smaller asymptomatic cancers