Stabilization in relation to wavenumber in HDG methods

Simulation of wave propagation through complex media relies on proper understanding of the properties of numerical methods when the wavenumber is real and complex. Numerical methods of the Hybrid Discontinuous Galerkin (HDG) type are considered for simulating waves that satisfy the Helmholtz and Maxwell equations. It is shown that these methods, when wrongly used, give rise to singular systems for complex wavenumbers. A sufficient condition on the HDG stabilization parameter for guaranteeing unique solvability of the numerical HDG system, both for Helmholtz and Maxwell systems, is obtained for complex wavenumbers. For real wavenumbers, results from a dispersion analysis are presented. An asymptotic expansion of the dispersion relation, as the number of mesh elements per wave increase, reveal that some choices of the stabilization parameter are better than others. To summarize the findings, there are values of the HDG stabilization parameter that will cause the HDG method to fail for complex wavenumbers. However, this failure is remedied if the real part of the stabilization parameter has the opposite sign of the imaginary part of the wavenumber. When the wavenumber is real, values of the stabilization parameter that asymptotically minimize the HDG wavenumber errors are found on the imaginary axis. Finally, a dispersion analysis of the mixed hybrid Raviart-Thomas method showed that its wavenumber errors are an order smaller than those of the HDG method

Ahorro y crecimiento: alguna evidencia para la economía argentina, 1970-2004

This paper investigates the factors that have influenced the savings behaviour in the Argentine economy. First, the correlations between saving and investment over time are analysed (the Feldstein- Horioka puzzle). Second, the paper investigates the causality in Granger sense between private national saving and real product in VAR models. The paper uses annual data during the 1970-2004 period.national saving, domestic investment, real output (real GDP), causality

Flujos netos de capital, choques macroeconómicos y activos de reservas. El caso argentino (1994-2013)

International reserves have been used as a source of protection against the vulnerability of the balance of payments, or alternatively, as an attempt to keep a competitive real exchange rate and to promote exports -- This paper explores the correlation between the net capital flows and reserves -- Similarly, the impact of some macroeconomic shocks on that variable is assessed -- Estimates are carried out through both, the VEC (Vector Error Correction) models and quarterly data of the Argentine economy for the period 1994-2013 -- Results show a negative correlation between international reserves and net capital flows (reserve accumulation through current account surpluses) -- At the same time, the expansionary fiscal policies and the continuing and widespread price increases would adversely affect the reservesLas reservas internacionales han sido empleadas como una fuente de protección contra la vulnerabilidad de la balanza de pagos, o alternativamente, para intentar mantener un tipo de cambio real competitivo y promover las exportaciones -- En este trabajo se analiza la correlación existente entre los flujos netos de capital y las reservas y se evalúa el efecto de algunos choques macroeconómicos en dicha variable -- Las estimaciones se realizan con modelos de VEC (modelo de corrección de errores) y datos trimestrales de la economía argentina, que cubren el período 1994-2013 -- Los resultados muestran una correlación negativa entre las reservas internacionales y los flujos netos de capital (acumulación de reservas a través de excedentes en la cuenta corriente) -- A su vez, las políticas fiscales expansivas y los aumentos persistentes y generalizados de precios afectarían negativamente a las reserva

A hybridizable discontinuous Galerkin method for solving nonlocal optical response models

We propose Hybridizable Discontinuous Galerkin (HDG) methods for solving the frequency-domain Maxwell's equations coupled to the Nonlocal Hydrodynamic Drude (NHD) and Generalized Nonlocal Optical Response (GNOR) models, which are employed to describe the optical properties of nano-plasmonic scatterers and waveguides. Brief derivations for both the NHD model and the GNOR model are presented. The formulations of the HDG method are given, in which we introduce two hybrid variables living only on the skeleton of the mesh. The local field solutions are expressed in terms of the hybrid variables in each element. Two conservativity conditions are globally enforced to make the problem solvable and to guarantee the continuity of the tangential component of the electric field and the normal component of the current density. Numerical results show that the proposed HDG methods converge at optimal rate. We benchmark our implementation and demonstrate that the HDG method has the potential to solve complex nanophotonic problems.Comment: 21 pages, 8figure

Determinantes económicos del nivel de empleo. Alguna evidencia para Argentina

Durante los años noventa, algunos países en desarrollo emprendieron reformas en el mercado de trabajo y abrieron sus economías al resto del mundo, medidas que no se tradujeron, como se esperaba, en mejoras sustanciales para los niveles de empleo e ingresos en esas economías. Argentina, en cambio, adoptó en años recientes una política tendiente a proteger el mercado doméstico, lo cual permitió aumentar considerablemente el nivel de empleo. En este trabajo, se analiza el mercado de trabajo argentino a partir de una ecuación de demanda laboral y de modelos VEC (modelo de corrección de equilibrio vectorial), de acuerdo con la propuesta de Johansen (1988) y Johansen y Juselius (1990), para el período 1994:3- 2011:2. Clasificación JEL: J08, J23, E24, F16

Choques de política fiscal, consumo privado, inversión y otras variables macroeconómicas. El caso de Argentina

Este artículo analiza los efectos de los choques de política fiscal sobre el consumo privado, la inversión y otras variables macroeconómicas de la economía argentina. Se usan modelos VAR estructurales con restricciones contemporáneas y datos trimestrales del periodo 1993-2012. El aumento del gasto del gobierno tiene efectos positivos sobre el consumo privado y la inversión, y reduce el desempleo. Las pruebas de causalidad indican que las variaciones de los ingresos tributarios preceden a las del consumo privado y la inversión

A Two-Level Parallelization Strategy for Genetic Algorithms Applied to Shape Optimum Design

This report presents a two-level strategy for the parallelization of a genetic algorithm coupled to a compressible flow solver designed on unstructured triangular meshes. The parallel implementation is based on MPI and makes use of the process group features of this environment. The resulting algorithm is used for the optimum shape design of aerodynamic configurations. Numerical and performance results are presented for the optimization of two-dimensional airfoils for calulations performed on the following systems : a SGI Origin 2000 and a IBM SP-2 MIMD systems; a Pentium Pro (P6/200 Mhz) cluster where the interconnection is realized through a FastEthernet (100 Mbits/s) switch

Application of a CFD validated model to plan fan heater position within flour mills during a heat treatment for insect pest control

The development of environmentally-friendly methods as alternatives to chemical fumigation for controlling insect pests has attracted public attention. Among these methods, heat treatment is based on the use of fan heaters that are positioned by operators who typically establish their number and position within buildings to be treated. The aim of this research was to improve heat treatment effectiveness by applying a validated computational fluid dynamics (CFD) model for planning fan heater positions within the building environment. Based on a CFD model, which was built and validated according to experimental data acquired during heat treatment of a flour mill, simulations were carried out by changing the position and/or rotation of fan heaters with the aim of enhancing temperature distribution inside the building. The results showed that in some simulations the percentage of internal wall surfaces having a temperature value lower than that required for heat treatment efficacy was considerably reduced, by up to 56.7%. Therefore, the CFD approach proposed in this study could be used as a decision support system for improving heat treatment efficacy

Choques de precios de materias primas, desempeño fiscal y crecimiento. Una propuesta de VAR estructural para la economía argentina

The international prices of commodities have increased markedly in recent years, driven by growth in China, India and other developing countries, which has had a positive impact on the economies of exporting these products. This paper analyzes the dynamics of changes in the prices of commodities on output growth and fiscal variables, in the case of Argentina. To this end, we use a structural VAR approach, with short-term restrictions, which allows nominal shocks in the international prices of commodities a_ect tax revenues, government consumer expenditures and output growth.International prices of commodities, tax revenues, government consumer expenditures, output growth, structural VAR.

High-performance parallel analysis of coupled problems for aircraft propulsion

This research program deals with the application of high-performance computing methods for the analysis of complete jet engines. We have entitled this program by applying the two dimensional parallel aeroelastic codes to the interior gas flow problem of a bypass jet engine. The fluid mesh generation, domain decomposition, and solution capabilities were successfully tested. We then focused attention on methodology for the partitioned analysis of the interaction of the gas flow with a flexible structure and with the fluid mesh motion that results from these structural displacements. This is treated by a new arbitrary Lagrangian-Eulerian (ALE) technique that models the fluid mesh motion as that of a fictitious mass-spring network. New partitioned analysis procedures to treat this coupled three-component problem are developed. These procedures involved delayed corrections and subcycling. Preliminary results on the stability, accuracy, and MPP computational efficiency are reported