Role of transverse displacements in the formation of subaqueous barchan dunes

Crescentic shape dunes, known as barchan dunes, are formed by the action of a fluid flow on a granular bed. These bedforms are common in many environments, existing under water or in air, and being formed from grains organized in different initial arrangements. Although they are frequently found in nature and industry, details about their development are still to be understood. In a recent paper [C. A. Alvarez and E. M. Franklin, Phys. Rev. E 96, 062906 (2017)], we proposed a timescale for the development and equilibrium of single barchans based on the growth of their horns. In the present Letter, we report measurements of the growth of horns at the grain scale. In our experiments, conical heaps were placed in a closed conduit and individual grains were tracked as each heap, under the action of a water flow, evolved into a barchan dune. We identified the trajectories of the grains that migrated to the growing horns, and found that most of them came from upstream regions on the periphery of the initial heap, with an average displacement of the order of the heap size. In addition, we show that individual grains had transverse displacements by rolling and sliding that are not negligible, with many of them going around the heap. The mechanism of horns formation revealed by our experiments contrasts with the general picture that barchan horns form from the advance of the lateral dune flanks due to the scaling of migration velocity with the inverse of dune size. Our results change the way in which the growth of subaqueous barchan dunes is explained12116CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP140773/2016-9; 400284/2016-22016/13474-9C. A. A. is grateful to SENESCYT (Grant No. 2013- AR2Q2850) and to CNPq (Grant No. 140773/2016-9). E. M. F. is grateful to FAPESP (Grant No. 2016/13474-9), to CNPq (Grant No. 400284/2016-2) and to FAEPEX/ UNICAMP (Grant No. 2210/18) for the financial support provide

Birth of a subaqueous barchan dune

Barchan dunes are crescentic shape dunes with horns pointing downstream. The present paper reports the formation of subaqueous barchan dunes from initially conical heaps in a rectangular channel. Because the most unique feature of a barchan dune is its horns, we associate the time scale for the appearance of horns to the formation of a barchan dune. A granular heap initially conical was placed on the bottom wall of a closed conduit and it was entrained by a water flow in turbulent regime. After a certain time, horns appear and grow, until an equilibrium length is reached. Our results show the existence of the time scales 0.5tc and 2.5tc for the appearance and equilibrium of horns, respectively, where tc is a characteristic time that scales with the grains diameter, gravity acceleration, densities of the fluid and grains, and shear and threshold velocities966CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP140773/2016-9; 400284/2016-22012/19562-6; 2016/13474-9Carlos A. Alvarez is grateful to SENESCYT Grant No. 2013-AR2Q2850) and to CNPq (Grant No. 140773/2016-9). Erick M. Franklin is grateful to FAPESP (Grants No. 2012/19562-6 and No. 2016/13474-9), to CNPq (Grant No. 400284/2016-2), and to FAEPEX/UNICAMP (Grant No. 2210/17) for the financial support provide

A Fresh Catch of Massive Binaries in the Cygnus OB2 Association

Massive binary stars may constitute a substantial fraction of progenitors to supernovae and gamma-ray bursts, and the distribution of their orbital characteristics holds clues to the formation process of massive stars. As a contribution to securing statistics on OB-type binaries, we report the discovery and orbital parameters for five new systems as part of the Cygnus OB2 Radial Velocity Survey. Four of the new systems (MT070, MT174, MT267, and MT734 (a.k.a. VI Cygni #11) are single-lined spectroscopic binaries while one (MT103) is a double-lined system (B1V+B2V). MT070 is noteworthy as the longest period system yet measured in Cyg OB2, with P=6.2 yr. The other four systems have periods ranging between 4 and 73 days. MT174 is noteworthy for having a probable mass ratio q<0.1, making it a candidate progenitor to a low-mass X-ray binary. These measurements bring the total number of massive binaries in Cyg OB2 to 25, the most currently known in any single cluster or association.Comment: Accepted for publication in the Astrophysical Journa

El delito político y las posibilidades de reconciliación en Colombia

PresentationEditoria

Araque Moreno, Diego, Lecciones de Derecho Penal. Introducción y Fundamentos de Imputación de responsabilidad, Bogotá, Ibáñez, 2016

Araque Moreno, Diego, Lecciones de Derecho Penal. Introducción y Fundamentos de Imputación de responsabilidad, Bogotá, Ibáñez, 201

Los Clúster del Sistema Regional de Innovación Antioqueño: Más Debilidades que Fortalezas en su Desempeño

This article is initially international contextualization of origin, current state and prospects of the concept of regional innovation system (RIS). Then they show characteristics of successful or SRI developed countries over the characteristics of SRI in developing countries. Later we will show how the identification process, support, implementation and consolidation of microcluster in Antioquia (backbone of the activities of SRI Antioquia) not due to a regional development strategy and that did not involve all its institutions (including scientific environments, productive, social, technological and financial). Finally, set the current scene (SWOT analysis, emphasizing the deficiencies and inadequacies) microcluster policy as central to the activities of SRI Antioquia.En este artículo se realiza inicialmente una contextualización internacional del origen, estado actual y perspectivas del concepto de sistema regional de innovación (SRI). Luego se mostrarán características de los SRI exitosos o de los países desarrollados frente a las características de los SRI de países en desarrollo. Posteriormente se mostrará cómo el proceso de identificación, apoyo, implementación y consolidación de los Microclusters en Antioquia (Eje central de las actividades del SRI Antioqueño) no obedece a una estrategia de desarrollo regional ya que no involucra toda su institucionalidad (incluyendo los entornos científico, productivo, social, tecnológico y financiero). Finalmente, se establece el panorama actual (análisis DOFA, haciendo énfasis en las deficiencias e insuficiencias) de la política de microcluster como eje central de las actividades del SRI antioqueño

Strong Constraints on the Parameter Space of the MSSM from Charge and Color Breaking Minima

A complete analysis of all the potentially dangerous directions in the field-space of the minimal supersymmetric standard model is carried out. They are of two types, the ones associated with the existence of charge and color breaking minima in the potential deeper than the realistic minimum and the directions in the field-space along which the potential becomes unbounded from below. The corresponding new constraints on the parameter space are given in an analytic form, representing a set of necessary and sufficient conditions to avoid dangerous directions. They are very strong and, in fact, there are extensive regions in the parameter space that become forbidden. This produces important bounds, not only on the value of $A$, but also on the values of $B$ and $M_{1/2}$. Finally, the crucial issue of the one-loop corrections to the scalar potential has been taken into account in a proper way.Comment: 48 pages, LaTeX, 12 uuencoded postscript figures in additional file. Only a small comment about the m=0 (no-scale) limit has been included in sect.6 (Results) and sect.7 (Conclusions

Global Stability of a Premixed Reaction Zone (Time-Dependent Liñan’s Problem)

Global stability properties of a premixed, three-dimensional reaction zone are considered. In the nonadiabatic case (i.e., when there is a heat exchange between the reaction zone and the burned gases) there is a unique, spatially one-dimensional steady state that is shown to be unstable (respectively, asymptotically stable) if the reaction zone is cooled (respectively, heated) by the burned mixture. In the adiabatic case, there is a unique (up to spatial translations) steady state that is shown to be stable. In addition, the large-time asymptotic behavior of the solution is analyzed to obtain sufficient conditions on the initial data for stabilization. Previous partial numerical results on linear stability of one-dimensional reaction zones are thereby confirmed and extended

Effect of Prosopis flexuosa on understory species and its importance to pastoral management in woodlands of the Central Monte Desert

In the Monte Biogeographic Province, located in the arid region of Argentina, the presence of Prosopis flexuosa DC. produces spatial heterogeneity through edaphic modifications and microclimate changes. This results in vegetation patches differing in species composition and abundance. However, this interaction can be modified by the occurrence of gradients of biotic stress or disturbance intensity. In particular, grazing has been observed to enhance or reduce vegetation heterogeneity. Such complex of interactions could determine forage availability for cattle in one of the driest areas of the Monte Desert. We assessed the effect of Prosopis on understory species and analyzed whether the outcomes of this interaction differed with distance to watering points, as a proxy of grazing intensity, in the Northeast of Mendoza Province, Argentina. We used a two-way factorial design including the following factors: 1) microsite (under the cover of P. flexuosa trees and in intercanopy microsites) and 2) distance to watering points ("near the watering point", 500-700 m away, and "far from the watering point", 3-4 km away). Cover of each species, total cover, bare soil, and litter were recorded, and plant diversity, richness, and evenness were estimated with the modified Point Quadrat method. Results showed that P. flexuosa cover, distance from watering points, and the interaction between them determined species composition, abundance and spatial distribution of understory species, and were, consequently, a determining factor for forage availability. The presence of P. flexuosa enhances carrying capacity by supporting higher abundance of grasses under its canopy. Near watering points, high grazing intensity appears to disrupt the patches formed under P. flexuosa canopies, reducing the differences between microsites.In the Monte Biogeographic Province, located in the arid region of Argentina, the presence of Prosopis flexuosa DC. produces spatial heterogeneity through edaphic modifications and microclimate changes. This results in vegetation patches differing in species composition and abundance. However, this interaction can be modified by the occurrence of gradients of biotic stress or disturbance intensity. In particular, grazing has been observed to enhance or reduce vegetation heterogeneity. Such complex of interactions could determine forage availability for cattle in one of the driest areas of the Monte Desert. We assessed the effect of Prosopis on understory species and analyzed whether the outcomes of this interaction differed with distance to watering points, as a proxy of grazing intensity, in the Northeast of Mendoza Province, Argentina. We used a two-way factorial design including the following factors: 1) microsite (under the cover of P. flexuosa trees and in intercanopy microsites) and 2) distance to watering points ("near the watering point", 500-700 m away, and "far from the watering point", 3-4 km away). Cover of each species, total cover, bare soil, and litter were recorded, and plant diversity, richness, and evenness were estimated with the modified Point Quadrat method. Results showed that P. flexuosa cover, distance from watering points, and the interaction between them determined species composition, abundance and spatial distribution of understory species, and were, consequently, a determining factor for forage availability. The presence of P. flexuosa enhances carrying capacity by supporting higher abundance of grasses under its canopy. Near watering points, high grazing intensity appears to disrupt the patches formed under P. flexuosa canopies, reducing the differences between microsites