A momentum-conserving, consistent, Volume-of-Fluid method for incompressible flow on staggered grids

The computation of flows with large density contrasts is notoriously difficult. To alleviate the difficulty we consider a consistent mass and momentum-conserving discretization of the Navier-Stokes equation. Incompressible flow with capillary forces is modelled and the discretization is performed on a staggered grid of Marker and Cell type. The Volume-of-Fluid method is used to track the interface and a Height-Function method is used to compute surface tension. The advection of the volume fraction is performed using either the Lagrangian-Explicit / CIAM (Calcul d'Interface Affine par Morceaux) method or the Weymouth and Yue (WY) Eulerian-Implicit method. The WY method conserves fluid mass to machine accuracy provided incompressiblity is satisfied which leads to a method that is both momentum and mass-conserving. To improve the stability of these methods momentum fluxes are advected in a manner "consistent" with the volume-fraction fluxes, that is a discontinuity of the momentum is advected at the same speed as a discontinuity of the density. To find the density on the staggered cells on which the velocity is centered, an auxiliary reconstruction of the density is performed. The method is tested for a droplet without surface tension in uniform flow, for a droplet suddenly accelerated in a carrying gas at rest at very large density ratio without viscosity or surface tension, for the Kelvin-Helmholtz instability, for a falling raindrop and for an atomizing flow in air-water conditions

Primeras tablas de selvicultura a la carta para masas regulares de Pinus nigra Arn. del Prepirineo Catalán

Three detailed management models are developed for even-aged black pine (Pinus nigra Arn.) stands of the Pyrenees. These models consist of a descriptive part, named Final Stand Type, from the first thinning to the regeneration concepts. Several goals to be reached in terms of final medium diameters and rotations are defined for each site index class. This part is complemented by Management Tables that represent quantitatively the stand evolution according to the proposed treatment regimen.Starting by a selective thinning combined with low thinning, weights and rotations of interventions are spread out at intervals depending on the growth dynamics of the species in the different site index classes. Finally, comparative economic valuation is carried out between the proposed models and the management as uneven-aged forest, which is the traditional management method of these stands in the Pyrenees.Se proponen modelos de gestión detallados para el pino laricio (Pinus nigra Arn.) del Pirineo. Los modelos constan de una parte descriptiva del régimen de tratamientos, denominada Tipo de Bosque Final, desde los primeros clareos hasta las cortas de regeneración, en los que en función de la calidad se definen objetivos a alcanzar en términos de diámetros medios finales y turno. esta se complementa con unas Tablas de Selvicultura a la carta que plasman cuantitativamente la evolución de la masa de acuerdo con el régimen de tratamientos propuesto. Se parte de las claras selectivas mixtas seguida de una clara por lo bajo como tipo de clara, escalonándose los pesos y rotaciones de las intervenciones en función de la dinámica de crecimiento de la especie en las distintas calidades de estación. Por último se realiza una valoración económica comparativa entre los modelos propuestos y la gestión como masa irregular, método tradicional de gestión de estos bosques en el Prepirineo catalán

PArallel, Robust, Interface Simulator (PARIS)

Paris (PArallel, Robust, Interface Simulator) is a finite volume code for simulations of immiscible multifluid or multiphase flows. It is based on the "one-fluid" formulation of the Navier-Stokes equations where different fluids are treated as one material with variable properties, and surface tension is added as a singular interface force. The fluid equations are solved on a regular structured staggered grid using an explicit projection method with a first-order or second-order time integration scheme. The interface separating the different fluids is tracked by a Front-Tracking (FT) method, where the interface is represented by connected marker points, or by a Volume-of-Fluid (VOF) method, where the marker function is advected directly on the fixed grid. Paris is written in Fortran95/2002 and parallelized using MPI and domain decomposition. It is based on several earlier FT or VOF codes such as Ftc3D, Surfer or Gerris. These codes and similar ones, as well as Paris, have been used to simulate a wide range of multifluid and multiphase flows

Online distributed leadership: A content analysis of interaction and teacher reflections on computer-supported learning

This study performs a content analysis of the communication that develops in online educational situations. It focuses on two aspects of communication in a context in which we observe instructional leadership: how leadership is seen in the virtual classroom and how teachers view their role. The study attempts to answer the question of how teachers lead this methodological change, that is, instructional leadership at the service of distributed leadership. The study analyses the online interaction and teachers’ reflections on the communication between teachers and students in the process of virtual teaching, specifically in post compulsory secondary education in Spain.Study financed by an R&D project in the area of Education Sciences Management entitled ‘Learning-Focused Leadership and its Impact on Improvement: Practices and Results in Secondary Education’, under the Subprogram for basic, non-oriented research projects. National Plan for R&D, 2010 Competition

Internal structure of virtual communications in communities of inquiry in higher education: Phases, evolution and participants’ satisfaction

This study investigates the phases of development of synchronous and asynchronous virtual communication produced in a community of inquiry (CoI) by analyzing the internal structure of each intervention in the forum and each chat session to determine the evolution of their social, cognitive and teaching character. It also analyzes the participating higher education students’ satisfaction with the activities, with the professors’ actions, and with themselves. We use a mixed methodology that includes content analysis of the virtual communications by crossing two categorization systems: (1) type of communication according to the model adopted from Garrison, Anderson and Archer (social, cognitive and teaching presence) and (2) phases in the evolution of the communication (initiation, proposal, development, opinion/closing and good-byes). The data are relevant to the students’ satisfaction and grades earned. The results suggest differences in the quantity and content of the communication in each phase and an evolution from social to cognitive elements, ending with social contributions. The students are satisfied with the virtual communications related to both the activities and the professors and evaluate themselves positively

Scalable Rules for Coherent Group Motion in a Gregarious Vertebrate

Individuals of gregarious species that initiate collective movement require mechanisms of cohesion in order to maintain advantages of group living. One fundamental question in the study of collective movement is what individual rules are employed when making movement decisions. Previous studies have revealed that group movements often depend on social interactions among individual members and specifically that collective decisions to move often follow a quorum-like response. However, these studies either did not quantify the response function at the individual scale (but rather tested hypotheses based on group-level behaviours), or they used a single group size and did not demonstrate which social stimuli influence the individual decision-making process. One challenge in the study of collective movement has been to discriminate between a common response to an external stimulus and the synchronization of behaviours resulting from social interactions. Here we discriminate between these two mechanisms by triggering the departure of one trained Merino sheep (Ovis aries) from groups containing one, three, five and seven naïve individuals. Each individual was thus exposed to various combinations of already-departed and non-departed individuals, depending on its rank of departure. To investigate which individual mechanisms are involved in maintaining group cohesion under conditions of leadership, we quantified the temporal dynamic of response at the individual scale. We found that individuals' decisions to move do not follow a quorum response but rather follow a rule based on a double mimetic effect: attraction to already-departed individuals and attraction to non-departed individuals. This rule is shown to be in agreement with an adaptive strategy that is inherently scalable as a function of group size

Parents’ perceptions and perspectives about their sons’ drug addiction and rehabilitation process

The family plays a key role in the development and progression of substance use disorder (SUD) either by inducing risk, or promoting protection and resilience. However, only a limited number of studies have addressed how the families of individuals with SUD experience and perceive drug addiction and what attitudes toward treatment they show. The purpose of this study was to explore and describe how the parents of two Puerto Rican adult men with a history of SUD understand this phenomenon using an interpretative phenomenological analysis. Results show that parents perceived SUD as a negative phenomenon, but their arguments regarding their sons’ drug addiction contained several misconceptions. Parents believed that the rehabilitation process was dependent primarily on their sons’ willpower and intelligence, and they also considered trust to be one of the most important elements to obtain family support. We conclude that these parents used past experiences and their immediate social reality to construct particular conceptualizations of their sons’ SUD. Our findings provide important information about family perception and perspectives that can be used for SUD treatment and prevention strategies

Realistic simulations of coaxial atomisation

We discuss advances in the methodology for Direct Numerical Simulations of coaxial atomization in typical experimental conditions. Such conditions are extremely demanding for the numerical methods. The key difficulty seems to be the combination of high density ratios, surface tension, and large Reynolds numbers. We explore how using a momentum-conserving Volume-Of-Fluid scheme allows to improve the stability and accuracy of the simulations. We show computational evidence that the use of momentum conserving methods allows to reduce the required number of grid points by an order of magnitude in the simple case of a falling rain drop. We then apply these ideas to coaxial atomization. We show that in moderate-size simulations in air-water conditions close to real experiments, instabilities are still present and then discuss ways to fix them. Among those, removing small VOF debris and improving the time-stepping scheme are two important directions.The accuracy of the simulations is then discussed in comparison with experimental results and in particular the angle of ejection of the structures. The code used for this research is free and distributed at http://parissimulator.sf.net