Corporate diversification and R&D intensity dynamics

We study the dynamic bidirectional relationship between firm R&D intensity and corporate diversification, using longitudinal data of Spanish manufacturing companies. Our empirical approach takes into account the censored nature of the dependent variables and the existence of firm-specific unobserved heterogeneity. Whereas we find a positive linear effect of R&D intensity on related diversification, the evidence about the effect of related diversification on R&D intensity takes the form of an inverted U. Hence, the effect of related diversification on R&D intensity is positive but marginally decreasing for moderate levels of related diversification, but such effect can turn out negative for high levels of related diversification. Additionally, the consequences of the dynamic relation are that the effects are substantially larger in the long-run than in the short-run

On the Whitham Hierarchies: Reductions and Hodograph Solutions

A general scheme for analyzing reductions of Whitham hierarchies is presented. It is based on a method for determining the $S$-function by means of a system of first order partial differential equations. Compatibility systems of differential equations characterizing both reductions and hodograph solutions of Whitham hierarchies are obtained. The method is illustrated by exhibiting solutions of integrable models such as the dispersionless Toda equation (heavenly equation) and the generalized Benney system.Comment: 24 page

Corporate diversification and R&D intensity dynamics

We study the dynamic bidirectional relationship between firm R&D intensity and corporate diversification, using longitudinal data of Spanish manufacturing companies. Our empirical approach takes into account the censored nature of the dependent variables and the existence of firm-specific unobserved heterogeneity. Whereas we find a positive linear effect of R&D intensity on related diversification, the evidence about the effect of related diversification on R&D intensity takes the form of an inverted U. Hence, the effect of related diversification on R&D intensity is positive but marginally decreasing for moderate levels of related diversification, but such effect can turn out negative for high levels of related diversification. Additionally, the consequences of the dynamic relation are that the effects are substantially larger in the long-run than in the short-run.

Delay and energy consumption analysis of frame slotted ALOHA variants for massive data collection in internet-of-things scenarios

This paper models and evaluates three FSA-based (Frame Slotted ALOHA) MAC (Medium Access Control) protocols, namely, FSA-ACK (FSA with ACKnowledgements), FSA-FBP (FSA with FeedBack Packets) and DFSA (Dynamic FSA). The protocols are modeled using an AMC (Absorbing Markov Chain), which allows to derive analytic expressions for the average packet delay, as well as the energy consumption of both the network coordinator and the end-devices. The results, based on computer simulations, show that the analytic model is accurate and outline the benefits of DFSA. In terms of delay, DFSA provides a reduction of 17% (FSA-FBP) and 32% (FSA-ACK), whereas in terms of energy consumption DFSA provides savings of 23% (FSA-FBP) and 28% (FSA-ACK) for the coordinator and savings of 50% (FSA-FBP) and 24% (FSA-ACK) for end-devices. Finally, the paper provides insights on how to configure each FSA variant depending on the network parameters, i.e., depending on the number of end-devices, to minimize delay and energy expenditure. This is specially interesting for massive data collection in IoT (Internet-of-Things) scenarios, which typically rely on FSA-based protocols and where the operation has to be optimized to support a large number of devices with stringent energy consumption requirementsPeer ReviewedPostprint (published version

Goodbye, ALOHA!

©2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The vision of the Internet of Things (IoT) to interconnect and Internet-connect everyday people, objects, and machines poses new challenges in the design of wireless communication networks. The design of medium access control (MAC) protocols has been traditionally an intense area of research due to their high impact on the overall performance of wireless communications. The majority of research activities in this field deal with different variations of protocols somehow based on ALOHA, either with or without listen before talk, i.e., carrier sensing multiple access. These protocols operate well under low traffic loads and low number of simultaneous devices. However, they suffer from congestion as the traffic load and the number of devices increase. For this reason, unless revisited, the MAC layer can become a bottleneck for the success of the IoT. In this paper, we provide an overview of the existing MAC solutions for the IoT, describing current limitations and envisioned challenges for the near future. Motivated by those, we identify a family of simple algorithms based on distributed queueing (DQ), which can operate for an infinite number of devices generating any traffic load and pattern. A description of the DQ mechanism is provided and most relevant existing studies of DQ applied in different scenarios are described in this paper. In addition, we provide a novel performance evaluation of DQ when applied for the IoT. Finally, a description of the very first demo of DQ for its use in the IoT is also included in this paper.Peer ReviewedPostprint (author's final draft

Testing the Forecasting Performance of Ibex 35 Option-implied Risk-neutral Densities

Published also as: Documento de Trabajo Banco de España 0504/2005.risk-neutral densities, forecasting performance

A history of Pyrenae. Fifty years of research and dissemination of Archaeology at the University of Barcelona (1965-2015)

En 1965, el Instituto de Arqueología y Prehistoria de la Universidad de Barcelona creó la revista Pyrenae como órgano de difusión de la investigación. La revista nacía como consecuencia de los enfrentamientos personales entre diferentes sectores de la investigación arqueológica en Cataluña y respuesta a una crisis institucional que estalló en 1960. Bajo la dirección de Joan Maluquer de Motes y Lluís Pericot, la revista aglutinó la mayor parte de los investigadores que se consideraban integrantes de la Escuela Arqueológica de Barcelona fundada por Pere Bosch Gimpera en 1916. A lo largo de cincuenta años, y en tres épocas sucesivas, Pyrenae se ha consolidado como una revista de referencia en el ámbito de la investigación arqueológica española y afronta su futuro con la intención de convertirse en un referente de la investigación sobre Prehistoria y Antigüedad en el Mediterráneo occidental.In 1965, the Institute of Archaeology and Prehistory, University of Barcelona created the journal Pyrenae as disseminator of research. The journal was born as a result of personal clashes between different sectors of archaeological research in Catalonia and response to an institutional crisis that erupted in 1960. Under the leadership of Joan Maluquer Motes and Lluís Pericot, the review brought together most of the researchers who considered themselves members of the Archaeological School of Barcelona founded by Pere Bosch Gimpera in 1916. Over fifty years, and in three successive times, Pyrenae has become a periodical of reference in the field of Spanish archaeological research and faces its future with the intention of becoming a reference for research on Prehistory and Antiquity in the Western Mediterranean