Arresting bubble coarsening: A two-bubble experiment to investigate grain growth in presence of surface elasticity

Many two-phase materials suffer from grain-growth due to the energy cost which is associated with the interface that separates both phases. While our understanding of the driving forces and the dynamics of grain growth in different materials is well advanced by now, current research efforts address the question of how this process may be slowed down, or, ideally, arrested. We use a model system of two bubbles to explore how the presence of a finite surface elasticity may interfere with the coarsening process and the final grain size distribution. Combining experiments and modelling in the analysis of the evolution of two bubbles, we show that clear relationships can be predicted between the surface tension, the surface elasticity and the initial/final size ratio of the bubbles. We rationalise these relationships by the introduction of a modified Gibbs criterion. Besides their general interest, the present results have direct implications for our understanding of foam stability

Development Cooperation and Dependency: An Analysis of Brazilian-Spanish Cooperation in Latin America Between 2010 and 2018

Based on analysis of Brazilian-Spanish cooperation in Latin America, this article aims to contribute to the discussion on whether South-South Cooperation (SSC) represents an alternative model with specific and differentiated objectives, or if it largely reproduces the constraints and interests traditionally associated with the North-South model, but with new institutions and actors. We start by analysing the main criticisms levelled at cooperation in the literature, emphasising the identification, review and comparison of the mechanisms of domination and dependency that derive from the bilateral and multilateral practices of traditional development cooperation. We then construct a synthetic dependency index to measure the ability of Spain and Brazil - as representative cases of North-South Cooperation (NSC) and SSC with Latin America - to influence the foreign trade, investment and foreign policy decisions of aid recipients, and to empirically contrast the lower level of verticality that much of the available literature assumes about SSC schemes. The empirical analysis suggests significant differences between NSC and SSC in terms of their ability to reproduce dependency patterns and validate the discourse that tends to identify the latter as an alternative cooperation model

Quantum spin fluctuations in the dipolar Heisenberg-like rare earth pyrochlores

The magnetic pyrochlore oxide materials of general chemical formula R2Ti2O7 and R2Sn2O7 (R = rare earth) display a host of interesting physical behaviours depending on the flavour of rare earth ion. These properties depend on the value of the total magnetic moment, the crystal field interactions at each rare earth site and the complex interplay between magnetic exchange and long-range dipole-dipole interactions. This work focuses on the low temperature physics of the dipolar isotropic frustrated antiferromagnetic pyrochlore materials. Candidate magnetic ground states are numerically determined at zero temperature and the role of quantum spin fluctuations around these states are studied using a Holstein-Primakoff spin wave expansion to order 1/S. The results indicate the strong stability of the proposed classical ground states against quantum fluctuations. The inclusion of long range dipole interactions causes a restoration of symmetry and a suppression of the observed anisotropy gap leading to an increase in quantum fluctuations in the ground state when compared to a model with truncated dipole interactions. The system retains most of its classical character and there is little deviation from the fully ordered moment at zero temperature.Comment: Latex2e, 18 pages, 4 figures, IOP forma

La agricultura marginal como fuente de sedimentos en el Pirineo Central

[Resumen] La agricultura cerealista ha ocupado grandes extensiones en los valles pirenaicos, en exposiciones solanas por debajo de 1600 m de altitud. En este artículo se estudia el papel de la agricultura tradicional en la producción de sedimentos y la degradación del paisaje. Por medio de parcelas experimentales puede afirmarse que la agricultura itinerante y el barbecho han dado lugar a pérdidas de suelo muy elevadas y explican la pedregosidad superficial de mu.chas laderas. En el caso de la agricultura itinerante (articas), la quema de matorral y la incorporación de cenizas al suelo como fertilizante no contribuía a mejorar sustancialmente la calidad de los suelos.[Abstract] Cereal cropping has occupied large extent in the Pyrenean valleys, on sunny aspects under 1.600 m a.s.l. In this paper the role of traditional farming on sediment yield and landscape degradation is studied. By means of experimental plots the authors conclude than shifting agriculture an fallow land have caused great soil losses and explain the surface stoniness in many hillslopes. In the case of shifting agriculture, the burning of the shrub cover and the use of ashes as fertilizer did not contribute to improve the quality of soil

Resolving Vega and the inclination controversy with CHARA/MIRC

Optical and infrared interferometers definitively established that the photometric standard Vega (alpha Lyrae) is a rapidly rotating star viewed nearly pole-on. Recent independent spectroscopic analyses could not reconcile the inferred inclination angle with the observed line profiles, preferring a larger inclination. In order to resolve this controversy, we observed Vega using the six-beam Michigan Infrared Combiner on the Center for High Angular Resolution Astronomy Array. With our greater angular resolution and dense (u,v)-coverage, we find Vega is rotating less rapidly and with a smaller gravity darkening coefficient than previous interferometric results. Our models are compatible with low photospheric macroturbulence and also consistent with the possible rotational period of ~0.71 days recently reported based on magnetic field observations. Our updated evolutionary analysis explicitly incorporates rapid rotation, finding Vega to have a mass of 2.15+0.10_-0.15 Msun and an age 700-75+150 Myrs, substantially older than previous estimates with errors dominated by lingering metallicity uncertainties (Z=0.006+0.003-0.002).Comment: Accepted for publication in ApJ Letter

Increasing the MTU size for Energy Efficiency in Ethernet

Abstract-The commonly used Maximum Transfer Unit (MTU) on the Internet has remained unchanged for many years at around 1500 bytes due mainly to backward compatibility issues. This is in contrast with link data rate, which has increased by several orders of magnitude. In this paper, a new advantage of using larger MTUs is introduced, namely Energy Efficiency. In wire-line environments, the link power consumption is generally roughly independent of the number of frames that are transmitted resulting in a poor energy efficiency. This will change with the development of standards like IEEE 802.3az, Energy Efficient Ethernet. This new standard allows a link to enter a low power mode when there are no frames to transmit therefore making power consumption almost proportional to the link load. In this context the use of larger MTUs minimizes the number of transitions between the active and low power modes thereby improving energy efficiency. The benefits of using larger MTUs in terms of energy efficiency are analyzed in this paper