Integration of streaming services and TCP data transmission in the Internet

We study in this paper the integration of elastic and streaming traffic on a same link in an IP network. We are specifically interested in the computation of the mean bit rate obtained by a data transfer. For this purpose, we consider that the bit rate offered by streaming traffic is low, of the order of magnitude of a small parameter \eps \ll 1 and related to an auxiliary stationary Markovian process (X(t)). Under the assumption that data transfers are exponentially distributed, arrive according to a Poisson process, and share the available bandwidth according to the ideal processor sharing discipline, we derive the mean bit rate of a data transfer as a power series expansion in \eps. Since the system can be described by means of an M/M/1 queue with a time-varying server rate, which depends upon the parameter \eps and process (X(t)), the key issue is to compute an expansion of the area swept under the occupation process of this queue in a busy period. We obtain closed formulas for the power series expansion in \eps of the mean bit rate, which allow us to verify the validity of the so-called reduced service rate at the first order. The second order term yields more insight into the negative impact of the variability of streaming flows

Chronicles of a disagreement foretold. CEPS Commentary, 28 November 2012

In the wake of the collapsed talks on a new EU budget for 2014-20, a new CEPS Commentary by Jorge Núñez Ferrer allows that there is a good chance that agreement will be reached before the summer but that the instrument will remain largely disconnected from the fundamental needs of the EU, foremost of which is the imperative to address imbalances in the eurozone

A Framework for Complexity Classes in Membrane Computing

The purpose of the present work is to give a general idea about the existing results and open problems concerning the study of complexity classes within the membrane computing framework. To this aim, membrane systems (seen as computing devices) are briefly introduced, providing the basic definition and summarizing the key ideas, trying to cover the various approaches that are under investigation in this area – of course, special attention is paid to the study of complexity classes. The paper concludes with some final remarks that hint the reasons why this field (as well as other unconventional models of computation) is attracting the attention of a growing community.Ministerio de Educación y Ciencia TIN2005-09345-C04-01Junta de Andalucía TIC-58

Interacting strings on AdS_3

We consider string theory on AdS_3 in terms of the Wakimoto free field representation. The scattering amplitudes for N unitary tachyons are analysed in the factorization limit and the poles corresponding to the mass-shell conditions for physical states are extracted. The vertex operators for excited levels are obtained from the residues and their properties are examined. Negative norm states are found at the second mass level.Comment: 24 pages, 2 figures, LaTeX. Substantial changes: ghosts found, conclusions modified accordingly, references added. Final version to appear in JHE