Bessel beam through a dielectric slab at oblique incidence: the case of total reflection

The oblique incidence of a Bessel beam on a dielectric slab with refractive index n1 surrounded by a medium of a refractive index n>n1 may be studied simply by expanding the Bessel beam into a set of plane waves forming the same angle with the axis of the beam. In the present paper we examine a Bessel beam that impinges at oblique incidence onto a layer in such a way that each plane-wave component impinges with an angle larger than the critical angle.Comment: 10 pages, 6 figure

A two-phase gradient method for quadratic programming problems with a single linear constraint and bounds on the variables

We propose a gradient-based method for quadratic programming problems with a single linear constraint and bounds on the variables. Inspired by the GPCG algorithm for bound-constrained convex quadratic programming [J.J. Mor\'e and G. Toraldo, SIAM J. Optim. 1, 1991], our approach alternates between two phases until convergence: an identification phase, which performs gradient projection iterations until either a candidate active set is identified or no reasonable progress is made, and an unconstrained minimization phase, which reduces the objective function in a suitable space defined by the identification phase, by applying either the conjugate gradient method or a recently proposed spectral gradient method. However, the algorithm differs from GPCG not only because it deals with a more general class of problems, but mainly for the way it stops the minimization phase. This is based on a comparison between a measure of optimality in the reduced space and a measure of bindingness of the variables that are on the bounds, defined by extending the concept of proportioning, which was proposed by some authors for box-constrained problems. If the objective function is bounded, the algorithm converges to a stationary point thanks to a suitable application of the gradient projection method in the identification phase. For strictly convex problems, the algorithm converges to the optimal solution in a finite number of steps even in case of degeneracy. Extensive numerical experiments show the effectiveness of the proposed approach.Comment: 30 pages, 17 figure

Localized fluidization in granular materials: Theoretical and numerical study

We present analytical and numerical results on localized fluidization within a granular layer subjected to a local injection of fluid. As the injection rate increases the three different regimes previously reported in the literature are recovered: homogeneous expansion of the bed, fluidized cavity in which fluidization starts developing above the injection area, and finally the chimney of fluidized grains when the fluidization zone reaches the free surface. The analytical approach is at the continuum scale, based on Darcy's law and Therzaghi's effective stress principle. It provides a good description of the phenomenon as long as the porosity of the granular assembly remains relatively homogeneous, i.e. for small injection rates. The numerical approach is at the particle scale based on the coupled DEM-PFV method. It tackles the more heterogeneous situations which occur at larger injection rates. The results from both methods are in qualitative agreement with data published independently. A more quantitative agreement is achieved by the numerical model. A direct link is evidenced between the occurrence of the different regimes of fluidization and the injection aperture. While narrow apertures let the three different regimes be distinguished clearly, larger apertures tend to produce a single homogeneous fluidization regime. In the former case, it is found that the transition between the cavity regime and the chimney regime for an increasing injection rate coincides with a peak in the evolution of inlet pressure. Finally, the occurrence of the different regimes is defined in terms of the normalized flux and aperture

Venezuela on the Edge of Bankruptcy: Prospects for Political Change

Venezuela, a South American petro-giant and the home of the Bolivarian socialist experiment, is in the grip of a grave crisis and an unprecedented political and institutional conflict, which has led to profound economic and social paralysis and a food and health emergency. As of 2019, Venezuela has the highest rate of inflation in the world and is struggling with an economic and social crisis characterised by violence and extreme poverty. In a paradoxical political situation, despite the crisis, the incumbent president Nicolas Maduro refuses to relinquish power while a new figure, Juan Guaidò, virtually unknown a year ago, having proclaimed himself president in January 2019, has been recognised politically by 54 nations, and is seeking a way out of the country’s ills. In the first quarter of 2019 alone in Venezuela, 96% of companies had to drastically reduce their staffing levels and commercial activities, while the average salary of a worker now corresponds to about four euros a month. In addition, in the last twenty years, i.e. since the arrival in power of the previous president, Hugo Chavez, four fifths of Venezuelan companies have closed down or ceased operating after being nationalised. Lastly, 84% of those who once had employment have now lost it. What the solutions to this situation may consist of is hard to say. This brief paper will look at the series of social and cultural obstacles that hamper any form political change. Cultural and social changes that can help resolve the current political and institutional conflict as soon as possible are required. The country has the largest oil reserves in the world, put at 296.5 billion barrels, and the fourth largest natural gas reserves in the world. In addition, it has the third largest reserves of fresh water on the planet and even possesses huge mineral resources, including gold and diamonds. Despite the variety of resources available, the Venezuelan economy is weighed down by the socialist policies of the government which has neither opened up to more liberal economic policies nor diversified economic investment, thus consolidating the country’s complete dependence on petroleum exports, which now account for 96% of the income from exports and 50% of state revenues

Shape Optimization for Thermal Insulation Problems

[EN] In this work we consider two domains: an external domain whose geometry varies, and an internal fixed one. From the thermal insulation viewpoint, we are considering a body to be insulated, enveloped in a layer of insulator, and we want to find the best shape for the thermal insulator, in terms of heat dispersion. Mathematically, our problem is described by an elliptic partial differential equation with Dirichlet-Robin boundary conditions.This research has been carried on within the PON R&I 2014-2020 - “AIM: Attraction and International Mobility” (Linea 2.1, project AIM1834118 - 2, CUP: E61G19000050001). The authors are members of the INdAM Research Group GNCS.Tozza, S.; Toraldo, G. (2022). Shape Optimization for Thermal Insulation Problems. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 11-15. https://doi.org/10.4995/YIC2021.2021.12288OCS111

Festival and Organization Studies

The present essay examines the festival as a form of organizing and as a metaphor for contemporary organizations. Drawing upon classical and contemporary perspectives on festival, we focus on social ambivalences and how these are enacted and mediated through festivals. Specifically, we argue that festivals mark a tension between linear and cyclical dimensions of social time. Next, we argue that formal institutional and communitarian principles are mediated through festival. Finally, we argue that festivals mark a tension between reflexivity and social critique on the one hand and mass spectacle on the other, and problematize the notion of bodily enjoyment as a form of social consciousness. We discuss the implications of these three ambivalences \u2013 in the notion of time, the notion of community and the notion of reflexivity \u2013 for contributing to contemporary organizational discussions

The geometry of the Landmark Task

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