Bursts in discontinuous Aeolian saltation

Close to the onset of Aeolian particle transport through saltation we find in wind tunnel experiments a regime of discontinuous flux characterized by bursts of activity. Scaling laws are observed in the time delay between each burst and in the measurements of the wind fluctuations at the fluid threshold Shields number $\theta_c$. The time delay between each burst decreases on average with the increase of the Shields number until sand flux becomes continuous. A numerical model for saltation including the wind-entrainment from the turbulent fluctuations can reproduce these observations and gives insight about their origin. We present here also for the first time measurements showing that with feeding it becomes possible to sustain discontinuous flux even below the fluid threshold

Vortex-line liquid phases: Longitudinal superconductivity in the lattice London model

We study the vortex-line lattice and liquid phases of a clean type-II superconductor by means of Monte Carlo simulations of the lattice London model. Motivated by a recent controversy regarding the presence, within this model, of a vortex-liquid regime with longitudinal superconducting coherence over long length scales, we directly compare two different ways to calculate the longitudinal coherence. For an isotropic superconductor, we interpret our results in terms of a temperature regime within the liquid phase in which longitudinal superconducting coherence extends over length scales larger than the system thickness studied. We note that this regime disappears in the moderately anisotropic case due to a proliferation, close to the flux-line lattice melting temperature, of vortex loops between the layers.Comment: 8 pages, Revtex, with eps figures. To appear in Phys. Rev.

Evolution of density perturbations in decaying vacuum cosmology: The case of non-zero perturbations in the cosmological term

We extend the results of a previous paper where a model of interacting dark energy, with a cosmological term decaying linearly with the Hubble parameter, is tested against the observed mass power spectrum. In spite of the agreement with observations of type Ia supernovas, baryonic acoustic oscillations and the cosmic microwave background, we had shown previously that no good concordance is achieved if we include the mass power spectrum. However, our analysis was based on the ad hoc assumption that the interacting cosmological term is strictly homogeneous. Now we perform a more complete analysis, by perturbing such a term. Although our conclusions are still based on a particular, scale invariant choice of the primordial spectrum of dark energy perturbations, we show that a cosmological term decaying linearly with the Hubble parameter is indeed disfavored as compared to the standard model.Comment: Version accepted for publication in Physical Review

Monte-Carlo calculation of longitudinal and transverse resistivities in a model Type-II superconductor

We study the effect of a transport current on the vortex-line lattice in isotropic type-II superconductors in the presence of strong thermal fluctuations by means of 'driven-diffusion' Monte Carlo simulations of a discretized London theory with finite magnetic penetration depth. We calculate the current-voltage (I-V) characteristics for various temperatures, for transverse as well as longitudinal currents I. From these characteristics, we estimate the linear resistivities R_xx=R_yy and R_zz and compare these with equilibrium results for the vortex-lattice structure factor and the helicity moduli. From this comparison a consistent picture arises, in which the melting of the flux-line lattice occurs in two stages for the system size considered. In the first stage of the melting, at a temperature T_m, the structure factor drops to zero and R_xx becomes finite. For a higher temperature T_z, the second stage takes place, in which the longitudinal superconducting coherence is lost, and R_zz becomes finite as well. We compare our results with related recent numerical work and experiments on cuprate superconductors.Comment: 4 pages, with eps figure

Jump at the onset of saltation

We reveal a discontinuous transition in the saturated flux for aeolian saltation by simulating explicitly particle motion in turbulent flow. The discontinuity is followed by a coexistence interval with two metastable solutions. The modification of the wind profile due to momentum exchange exhibits a second maximum at high shear strength. The saturated flux depends on the strength of the wind as $q_s=q_0+A(u_*-u_t)(u_*^2+u_t^2)$

Is this blended-learning, or another thing?

Today there are many forms of online use to support training, education and information dissemination. There's been a lot of confusion about the concept of online learning and we may not be able to get a definitive definition of it but hopefully, we can clarify concepts and the objective of this presentation is to be able to have a satisfying definition to understand the way our institution uses online content for our undergraduate students. Online learning in higher education is often pointed out as a good alternative, in the planning and organization of teaching/learning activities. Although there is resistance to its adherence by older or traditionalist teachers, because they do not master the tools and pedagogical innovation with digital technologies and also some resistance to the format, as it seconds the role of the teacher, shifting the axis of learning towards the student. Our University uses currently a platform for online learning, where there are small online courses that are additinally for some of the mandatory or optative curricular courses for the first year of the Undergraduate Programme. The structure of the online courses is normally of videos in varying number, followed by quizzes to assess the knowledge retained by the viewer of the video. It requires a minimum percentage of result to proceed to the next video. This model for training and education gives both the student and the teacher the opportunity of enrichment if, on the one hand, the student creates some autonomy, on the other hand, does not lose contact with teacher presence.info:eu-repo/semantics/acceptedVersio

21st century skills and digital skills, are one and the same thing?

The preparation of students of new generations for the labour market and for new social contexts currently requires higher education (ES) to reflect and reorganize its learning and training offer. In this sense, higher education institutions (HEIs) need to pursue a set of challenges, which include identifying and understanding the characteristics and needs of new students generations. Over the last decade's reference models on transversal competences (soft skills) have been established, classifying them on several nomenclatures as instrumental, interpersonal and systemic, but not always considering the temporal, and social, economic context of these same references. With the aim of designing an adequate formative offer, we have developed a study based on the systematization of the literature on the extent of reference models, categorization and terminology of references, regarding competences skills and aptitudes, and reflect, if in some cases, we are talking about equal, different or complementary competences, in one single one. An asymmetry still seems evident between the needs for skills of a digitalized society and the development by HEIs of an educational offer convergent with these same needs, not only at the professional level but also of behavioural, emotional, social, cultural capacities. Moreover, unlike digital skills, 21st-century skills are not necessarily underpinned by digital technologies. If two decades ago the categorization terminology was limited to instrumental, interpersonal and systemic skills, the research in this area develops more detailed frameworks that do not separate 21st-century skills from digital skills, structuring this large set into foundation or fundamental, social and emotional skills to learn, create and innovate, emancipatory and humanistic and artistic skills. In addition, the discussion focuses on the ability of students to acquire and develop these new skills in an academic and professional context, leaving aside the ability of teachers to conduct and integrate those skills in a transversal and transdisciplinary in teaching and learning approaches.info:eu-repo/semantics/acceptedVersio