Foreclosing Competition through Access Charges and Price Discrimination

This article analyzes competition between two asymmetric networks, an incumbent and a new entrant. Networks compete in non-linear tariffs and may charge different prices for on-net and off-net calls. Departing from cost-based access pricing allows the incumbent to foreclose the market in a profitable way. If the incumbent benefits from customer inertia, then it has an incentive to insist in the highest possible access markup even if access charges are reciprocal and even in the absence of actual switching costs. If instead the entrant benefits from customer activism, then foreclosure is profitable only when switching costs are large enough.Access Pricing, Entry Deterrence, Interconnection, Network Competition, Two-way Access

Optimal education and pensions in an endogenous growth model

In OLG economies with life-cycle saving and exogenous growth, competitive equilibria in general fail to achieve optimality because individuals accumulate amounts of physical capital that differ from the one that maximizes welfare along a balanced growth path (the Golden Rule). With human capital, a second potential source of departure from optimality arises, related to education decisions. We propose to recover the Golden Rule of physical and also human capital accumulation. We characterize the optimal policy to decentralize the Golden Rule balanced growth path when there are no constraints for individuals to finance their education investments, and show that it involves education taxes. Also, when the government subsidizes the repayment of education loans, optimal pensions are positive

Autonomous use of a computer algebra system for learning linear algebra

A Computer Algebra System (CAS) can be defined as mathematical software with numerical, graphic and symbolic capacities. Many studies have addressed the teaching of mathematics in a CAS environment. This paper describes a teaching experience carried out in a linear algebra course, for engineering students, with methodologies adapted to the European Higher Education Area. Generic competences such as self-learning, team work or use of technology have been enhanced through autonomous work of students, who had worked in small groups (2-3 students) using a CAS for solving proposal exercises. The experience was completed with a competition which was announced and promoted between the students with the best grades. They developed a project related to a real problem in science or engineering, where orthogonal transformations are used for modelling and solving the problem. A brief summary of the winner project is included in the paper. The experiment proves that technology provides the students with material for enhancing the apprenticeship and improving the motivation

E-Assessment and mathematical learning: A Spanish overview

Assessment can be used to enhance student learning (formative assessment) or to control the apprenticeship (summative assessment). The two ways can be used according to the requirements or needs. Nowadays, the student must be the protagonist of his learning, and it is important that he receives immediate feedback of the learning process. The normal work or the real life for the current students includes the quick answers provided by technology. Therefore technology allows the development of new models of assessment easy to implement. Technology-supported assessments are already being used as a formative assessment and some influence in the summative sense of grading student achievement in some Spanish universities. After some general ideas concerning the learning process, this paper analyses the various ways in which technology is used in assessment activities of basic mathematical subjects in Spanish engineering degrees. The results are supported by the construction of a data base of Learning Guides (information provided by the universities to the students)

Business Effect Versus Industry Effect. An Empirical Study in Galician and Portuguese Firms

Texto dispoñible en galego e españolEste traballo é unha contribución á análise da importancia relativa dos factores industria e empresa na explicación da variabilidade do rendemento organizativo. Nel aplícase un modelo xerárquico lineal de efectos fixos a unha mostra de empresas de Galicia e do norte de Portugal. Os resultados obtidos mostran que a capacidade explicativa do factor empresa é cando menos cinco veces superior á do factor sector de actividade. Estes resultados favorables para o efecto empresa son similares aos alcanzados en estudos empíricos precedentesEste trabajo es una contribución al análisis de la importancia relativa de los factores industria y empresa en la explicación de la variabilidad del rendimiento organizativo. En él se aplica un modelo jerárquico lineal de efectos fijos a una muestra de empresas de Galicia y del norte de Portugal. Los resultados obtenidos muestran que la capacidad explicativa del factor empresa es al menos cinco veces superior a la del factor sector de actividad. Estos resultados favorables al efecto empresa son similares a los alcanzados en estudios empíricos precedentesThis work is a contribution to the analysis of the influence that industry and business factors have on the variability of the organizational performance. A linear hierarchical model with fixed effects is applied to a sample of Spanish and Portuguese firms. The results show that the portion of such variability explained by the business factor is at least five times greater than that explained by the industry factor. These results, in favour of the business effect, are similar to other obtained in previous empirical studiesS

Influence of Titanium Oxide Pillar Array Nanometric Structures and Ultraviolet Irradiation on the Properties of the Surface of Dental Implants: A Pilot Study

Aim: Titanium implants are commonly used as replacement therapy for lost teeth and much current research is focusing on the improvement of the chemical and physical properties of their surfaces in order to improve the osseointegration process. TiO2, when it is deposited in the form of pillar array nanometric structures, has photocatalytic properties and wet surface control, which, together with UV irradiation, provide it with superhydrophilic surfaces, which may be of interest for improving cell adhesion on the peri-implant surface. In this article, we address the influence of this type of surface treatment on type IV and type V titanium discs on their surface energy and cell growth on them. Materials and methods: Samples from titanium rods used for making dental implants were used. There were two types of samples: grade IV and grade V. In turn, within each grade, two types of samples were differentiated: untreated and treated with sand blasting and subjected to double acid etching. Synthesis of the film consisting of titanium oxide pillar array structures was carried out using plasma-enhanced chemical vapor deposition equipment. The plasma was generated in a quartz vessel by an external SLAN-1 microwave source with a frequency of 2.45 GHz. Five specimens from each group were used (40 discs in total). On the surfaces to be studied, the following determinations were carried out: (a) X-ray photoelectron spectroscopy, (b) scanning electron microscopy, (c) energy dispersive X-ray spectroscopy, (d) profilometry, (e) contact angle measurement or surface wettability, (f) progression of contact angle on applying ultraviolet irradiation, and (g) a biocompatibility test and cytotoxicity with cell cultures. Results: The application of ultraviolet light decreased the hydrophobicity of all the surfaces studied, although it did so to a greater extent on the surfaces with the studied modification applied, this being more evident in samples manufactured in grade V titanium. In samples made in grade IV titanium, this difference was less evident, and even in the sample manufactured with grade IV and SLA treatment, the application of the nanometric modification of the surface made the surface optically less active. Regarding cell growth, all the surfaces studied, grouped in relation to the presence or not of the nanometric treatment, showed similar growth. Conclusions. Treatment of titanium oxide surfaces with ultraviolet irradiation made them change temporarily into superhydrophilic ones, which confirms that their biocompatibility could be improved in this way, or at least be maintained

Lipoma intramuscular del músculo deltoides: Presentación de cuatro casos

Describimos cuatro casos de lipoma intramuscular del músculo deltoides en cuatro pacientes, dos mujeres y dos varones con una edad media de 62 años. Dos están situados en el lado derecho y dos en el izquierdo. Las tumoraciones tienen un tamaño que oscila entre 5 y 8 centímetros, produciendo un cuadro clínico de dolor y limitación funcional del hombro. En tres de los cuatro pacientes se realiza tratamiento definitivo con extirpación quirúrgica de la tumoración. Con un seguimiento mínimo de año y medio, no existe recidiva de la lesión y los pacientes muestran una recuperación clínica y funcional completa.We describe four intramuscular lipoma in the deltoids muscle, in four patients (two women and two men), 62 years old. Two of the tumors were localized in the right side and two in the left side. The tumor size was between 5 and 8 centimetres, causing pain and functional disability of the shoulder. Three of the four patients were treated by surgical extirpation of the tumors. 18 months after surgery, none of the tumors have recurred and all patients showed a total functional recovery

A toolbox with DERIVE: calculus on several variables, Applications of Computer Algebra

A toolbox is a set of procedures taking advantage of the computing power and graphical capacities of a CAS. With these procedures the students can solve math problems, apply mathematics to engineering or simply reinforce the learning of certain mathematical concepts. From the point of view of their construction, we can consider two types of toolboxes: (i) the closed box, built by the teacher, in which the utility files are provided to the students together with the respective tutorials and several worksheets with proposed exercises and problems

Reparación completa quirúrgica en adultos con situación Fallot no operada o solamente paliada: ¿ficción o realidad?

Introducción-objetivos: Los pacientes con situación Fallot sin operar o solamente paliados excepcionalmente sobreviven hasta la edad adulta. Si las arterias pulmonares tienen un calibre aceptable, creemos que la reparación completa quirúrgica es viable. A continuación, revisamos nuestra experiencia. Métodos: Estudio retrospectivo de 27 adultos con situación Fallot no operada o solo paliada y reparación completa quirúrgica entre 1991-2014. Resultados: Edad media ± desviación estándar: 35,6 ± 10,6 años, 59% varones, paliación previa 18,5%. Diagnóstico principal: ventrículo derecho bicameral + comunicación interventricular (48%), tetralogía de Fallot clásica (30%). Grado funcional NYHA: I-26%, II-30%, III-44%. Arritmia: 22%. Hematocrito medio: 49 ± 11%. Asociaban agenesia arteria pulmonar izquierda (11%), insuficiencia aórtica severa (11%). Las pruebas complementarias mostraban gradientes elevados entre ventrículo derecho-arteria pulmonar y buena contractilidad biventricular. Operados por esternotomía media con extracorpórea, hipotermia moderada y pinzamiento aórtico. Cierre de comunicación interventricular desde la aurícula derecha: 63%. Reconstrucción del tracto de salida derecho conservando la válvula pulmonar (78%), interponiendo bioprótesis (15%) y con parche transanular (7%). Cirugía asociada en 5 pacientes (18,5%): tricúspide (1), aórtica (4). Sin mortalidad hospitalaria. Seguimiento medio 8,4 ± 6,3 años (máximo 19,75). Un paciente fallece tardíamente. Reoperación en 3 pacientes (11%) por lesiones residuales. Actualmente grado funcional i65%, ii31%, iii4%, estando el 92% en ritmo sinusal. Conclusiones: La reparación completa del adulto con situación Fallot consigue mejoría clínica al eliminar la cianosis, cerrar los cortocircuitos intracardiacos y disminuir la sobrecarga de presión del ventrículo derecho. Esta reparación tiene resultados excelentes y permite superiores tasas de conservación del anillo pulmonar respecto a las series infantiles