Interchange fees in credit and debit card markets : what role for public authorities

Credit and especially debit card transactions are on the rise worldwide. Interchange fees are an integral part of the pricing structure of credit and debit card transactions. Indirectly paid by merchants to card issuers, interchange fees in most countries are set by credit and debit card networks. But in one country, Australia, the central bank is regulating interchange fees, and in several other countries and areas, including the European Union, Mexico, the Netherlands, Spain, and the United Kingdom, public officials are taking, or considering taking, a more hands-on regulatory stance. In the United States, it is largely the court system that is debating interchange issues. ; The payments industry has a strong vested interest in interchange fees. They are a major portion of costs that merchants pay for processing debit and credit card payments and are a major source of revenue for banks that issue the cards. One reason for recent interest in interchange fees in the United States is a shift in retail payments away from checks. Research sponsored by the Federal Reserve documents a rise in electronic payments and a decline in the use of paper checks, with a milestone recently passed where the majority of noncash payments are now made using electronic instruments. This shift is also occurring in other countries. Since paper checks typically do not have an interchange fee while credit and debit payments do, the shift is a major reason why merchants face a rapidly rising cost of processing payments. Card issuers, on the other hand, rely on associated revenues to provide a return to their substantial investment in card payment networks. ; Pacheco and Sullivan summarize the proceedings of a conference sponsored by the Federal Reserve Bank of Kansas City, held in Santa Fe, New Mexico, in May 2005, which explored issues surrounding interchange fees. The conference brought together a distinguished group of industry participants, antitrust authorities, central bankers, and academics.Credit cards ; Debit cards ; Payment systems

Political Institutions, Policymaking Processes, and Policy Outcomes in Venezuela

This case study of Venezuela`s democratic institution and policymaking processes is part of the broader regional project based on the theoretical framework developed by Spiller, Stein and Tommasi (2003). The framework focuses on the conditions that foster political cooperation among political actors to sustain inter-temporal policy commitments. The study shows that the political institutions that established Venezuela`s democracy in the 1960s were deliberately set up to generate a cooperative equilibrium with low stakes of power. Constitutionally weak presidents and strong centralized political parties characterized this institutional framework. Cooperation induced a relatively effective policymaking process and good policy outcomes. However, an oil boom and its aftermath, in the 1970s and 1980s, unraveled the cooperative framework and induced rapid economic decay. The political reforms implemented in the late 1980s to improve the democratic process, although in itself desirable, further weakened the party system and induced a highly uncooperative and volatile policymaking process. The recent political reforms, increasing the stakes of power, have stimulated a complete breakdown in cooperation and a highly polarized political system.

Accretion discs models with the "beta"-viscosity prescription derived from laboratory experiments

We examine under which conditions one may apply, to steady state keplerian accretion discs, the "beta"-viscosity prescription which has been derived from rotating shear flow experiments (Richard & Zahn 1999). Using a vertically averaged model, we show that this law may be suitable for all three families of known systems: in young stellar objects, evolved binary stars and Active Galactic Nuclei discs (except in their outer gas pressure dominated regions where turbulence becomes hypersonic). According to the standard criterion for viscous stability, "beta"-discs are always stable throughout. Using realistic opacities and equation of state, we demonstrate that these discs are thermally unstable in the temperature domain where hydrogen recombines, when they are optically thick, and this could lead to limit cycle behavior. Radiation pressure dominated regions are thermally stable, in contrast with "alpha"-discs. This results in a fully stable solution for the innermost parts of AGN discs.Comment: 8 pages, PostScript. accepted in Astron. & Astrophy

Robust stabilised finite element solvers for generalised Newtonian fluid flows

Various materials and solid-fluid mixtures of engineering and biomedical interest can be modelled as generalised Newtonian fluids, as their apparent viscosity depends locally on the flow field. Despite the particular features of such models, it is common practice to combine them with numerical techniques originally conceived for Newtonian fluids, which can bring several issues such as spurious pressure boundary layers, unsuitable natural boundary conditions and coupling terms spoiling the efficiency of nonlinear solvers and preconditioners. In this work, we present a finite element framework dealing with such issues while maintaining low computational cost and simple implementation. The building blocks of our algorithm are (i) an equal-order stabilisation method preserving consistency even for lowest-order discretisations, (ii) robust extrapolation of velocities in the time-dependent case to decouple the rheological law from the overall system, (iii) adaptive time step selection and (iv) a fast physics-based preconditioned Krylov subspace solver, to tackle the relevant range of discretisation parameters including highly varying viscosity. Selected numerical experiments are provided demonstrating the potential of our approach in terms of robustness, accuracy and efficiency for problems of practical interest

Efficient and Higher-Order Accurate Split-Step Methods for Generalised Newtonian Fluid Flow

[EN] In numerous engineering applications, such as polymer or blood flow, the dependence of fluid viscosity on the local shear rate plays an important role. Standard techniques using inf-sup stable finite elements lead to saddle-point systems posing a challenge even for state-ofthe-art solvers and preconditioners. Alternatively, projection schemes or time-splitting methods decouple equations for velocity and pressure, resulting in easier to solve linear systems. Although pressure and velocity correction schemes of high-order accuracy are available for Newtonian fluids, the extension to generalised Newtonian fluids is not a trivial task. Herein, we present a split-step scheme based on an explicit-implicit treatment of pressure, viscosity and convection terms, combined with a pressure Poisson equation with fully consistent boundary conditions. Then, using standard equal-order finite elements becomes possible. Stability, flexibility and efficiency of the splitting scheme is showcased in two challenging applications involving aortic aneurysm flow and human phonation.The authors gratefully acknowledge Graz University of Technology for the financial support of the Lead-project: Mechanics, Modeling and Simulation of Aortic Dissection.Schussnig, R.; Pacheco, D.; Kaltenbacher, M.; Fries, T. (2022). Efficient and Higher-Order Accurate Split-Step Methods for Generalised Newtonian Fluid Flow. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 335-344. https://doi.org/10.4995/YIC2021.2021.12217OCS33534

An efficient split-step framework for non-Newtonian incompressible flow problems with consistent pressure boundary conditions

Incompressible flow problems with nonlinear viscosity, as they often appear in biomedical and industrial applications, impose several numerical challenges related to regularity requirements, boundary conditions, matrix preconditioning, among other aspects. In particular, standard split-step or projection schemes decoupling velocity and pressure are not as efficient for generalised Newtonian fluids, since the additional terms due to the non-zero viscosity gradient couple all velocity components again. Moreover, classical pressure correction methods are not consistent with the non-Newtonian setting, which can cause numerical artifacts such as spurious pressure boundary layers. Although consistent reformulations have been recently developed, the additional projection steps needed for the viscous stress tensor incur considerable computational overhead. In this work, we present a new time-splitting framework that handles such important issues, leading to an efficient and accurate numerical tool. Two key factors for achieving this are an appropriate explicit–implicit treatment of the viscous and convective nonlinearities, as well as the derivation of a pressure Poisson problem with fully consistent boundary conditions and finite-element-suitable regularity requirements. We present first- and higher-order stepping schemes tailored for this purpose, as well as various numerical examples showcasing the stability, accuracy and efficiency of the proposed framework

Efficient split-step schemes for fluid–structure interaction involving incompressible generalised Newtonian flows

Blood flow, dam or ship construction and numerous other problems in biomedical and general engineering involve incompressible flows interacting with elastic structures. Such interactions heavily influence the deformation and stress states which, in turn, affect the engineering design process. Therefore, any reliable model of such physical processes must consider the coupling of fluids and solids. However, complexity increases for non-Newtonian fluid models, as used, e.g., for blood or polymer flows. In these fluids, subtle differences in the local shear rate can have a drastic impact on the flow and hence on the coupled problem. There, existing (semi-) implicit solution strategies based on split-step or projection schemes for Newtonian fluids are not applicable, while extensions to non-Newtonian fluids can lead to substantial numerical overhead depending on the chosen fluid solver. To address these shortcomings, we present here a higher-order accurate, added-mass-stable fluid–structure interaction scheme centered around a split-step fluid solver. We compare several implicit and semi-implicit variants of the algorithm and verify convergence in space and time. Numerical examples show good performance in both benchmarks and an idealised setting of blood flow through an abdominal aortic aneurysm considering physiological parameters

The Use and Misuse of OxyContin

This paper examines the phenomenon of OxyContin abuse over the past two years. The prescription painkiller has been hailed as both a wonder drug and a killer. Both descriptions are accurate. The trouble is not with the pill itself but rather the environment into which it was released. The medical community lacked the experience with pain and addiction necessary to prescribe the powerful drug appropriately. As OxyContin was released in 1995, neither its manufacturer nor governmental agencies did anything to remedy these circumstances or protect against the eventual outcome. After nearly four successful years on the market, ubiquitous reports of addiction and overdoses filled the headlines. While in many ways the extent of the problem has been overstated by the media, that one exists is undeniable. Distinct from the concurrent growth of prescription drug abuse in general, OxyContin abuse has been particularly devastating to those individuals and areas affected. The best solutions focus on deterring and combating abuse and diversion, while ensuring access to the drug for the millions who benefit from it

The growth of supermassive black holes fed by accretion disks

Supermassive black holes are probably present in the centre of the majority of the galaxies. There is a consensus that these exotic objects are formed by the growth of seeds either by accreting mass from a circumnuclear disk and/or by coalescences during merger episodes. The mass fraction of the disk captured by the central object and the related timescale are still open questions, as well as how these quantities depend on parameters like the initial mass of the disk or the seed or on the angular momentum transport mechanism. This paper is addressed to these particular aspects of the accretion disk evolution and of the growth of seeds. The time-dependent hydrodynamic equations were solved numerically for an axi-symmetric disk in which the gravitational potential includes contributions both from the central object and from the disk itself. The numerical code is based on a Eulerian formalism, using a finite difference method of second-order, according to the Van Leer upwind algorithm on a staggered mesh. The present simulations indicate that seeds capture about a half of the initial disk mass, a result weakly dependent on model parameters. The timescales required for accreting 50% of the disk mass are in the range 130-540 Myr, depending on the adopted parameters. These timescales permit to explain the presence of bright quasars at z ~ 6.5. Moreover, at the end of the disk evolution, a "torus-like" geometry develops, offering a natural explanation for the presence of these structures in the central regions of AGNs, representing an additional support to the unified model.Comment: 10 pages, 7 figures. Accepted for publication by Astronomy and Astrophysic