Optimal mobility-aware admission control in content delivery networks

This paper addresses the problem of mobility management in Content Delivery Networks (CDN). We introduce a CDN architecture where admission control is performed at mobility aware access routers. We formulate a Markov Modulated Poisson Decision Process for access control that captures the bursty nature of data and packetized traffic together with the heterogeneity of multimedia services. The optimization of performance parameters, like the blocking probabilities and the overall utilization, is conducted and the structural properties of the optimal solutions are also studied. Heuristics are proposed to encompass the computational difficulties of the optimal solution when several classes of multimedia traffic are considered

Social learning and information sharing: an evolutionary simulation model of foraging in Norway rats

Social learning is distinguished from innate behaviour and individual learning as a behavioural strategy. We investigate simple mechanisms for social learning in an evolutionary simulation of food-preference copying in Norway rats. These animals learn preferences by interacting with conspecifics, but, unexpectedly, they fail to learn aversions after interacting with a poisoned demonstrator. They also follow each other for food sites. Simulation results show that failure to discriminate between sick and healthy demonstrators may be due to food toxicity in foraging environments. A seemingly complex instance of social information transmission is explained through the action of simple behaviours in an appropriately structured environment

Cross-correlation of the CMB and radio galaxies in real, harmonic and wavelet spaces: detection of the integrated Sachs-Wolfe effect and dark energy constraints

We report the first detection of the ISW effect in wavelet space, at scales in the sky around 7 degrees with a significance of around 3.3 sigma, by cross-correlating the WMAP first-year data and the NRAO VLA Sky Survey (NVSS). In addition, we present a detailed comparison among the capabilities of three different techniques for two different objectives: to detect the ISW and to put constraints in the nature of the dark energy. The three studied techniques are: the cross-angular power spectrum (CAPS, harmonic space), the correlation function (CCF, real space) and the covariance of the Spherical Mexican Hat Wavelet (SMHW) coefficients (CSMHW, wavelet space). We prove that the CSMHW is expected to provide a higher detection of the ISW effect for a certain scale. This prediction has been corroborated by the analysis of the data. The SMHW analysis shows that the cross-correlation signal is caused neither by systematic effects nor foreground contamination. However, by taking into account the information encoded in all the multipoles/scales/angles, the CAPS provides slightly better constraints than the SMHW in the cosmological parameters that define the nature of the dark energy. The limits provided by the CCF are wider than for the other two methods. Two different cases have been studied: 1) a flat Lambda-CDM universe and 2) a flat universe with an equation of state parameter different from -1. In the first case, the CAPS provides (for a bias value of b = 1.6) 0.59 < Lambda density < 0.84 (at 1 sigma CL). Moreover, the CAPS rejects the range Lambda density < 0.1 at 3.5 sigma, which is the highest detection of the dark energy reported up to date. In the second case, the CAPS gives 0.50 < dark energy density < 0.82 and -1.16 < w < 0.43 (at 1 sigma CL).Comment: 12 pages, 7 figures, accepted for publication in MNRAS. Analysis redone. Changes in the estimation of the cosmological parametres. Additional comparison between wavelets and more standard technique

Agent-based modeling of interdependent critical infrastructures

Critical interdependent infrastructures are complex systems, that if damaged or disrupted can seriously compromise the welfare of our society. This research, part of the CRESCO project, deal with the problem of interdependent critical infrastructures analysis, proposing an agent-based modelling and simulation solution. The approach we put forward, named Federated-ABMS, relies on discrete agent-based modelling and simulation and federated simulation. Federated-ABMS provides a formalism to model compound complex systems, composed of interacting systems, as federation of interacting agents and sector specific simulation models. This paper describes the formal model as well it outlines the steps that characterise the Federated-ABMS methodology, here applied to a target system, composed of a communication network and of a power grid. Moreover we conclude the paper with a thorough discussion of implementation issues

SUPPLY CHAIN MANAGEMENT AND THE ROMANIAN TRANSITION

Supply Chain Management (SCM), defined here as the construction of productive systems spanning over organizational borders with suppliers and customers and integrated via human-based and information technology systems to satisfy final customer requirements, is introduced as a key concept to accelerate Romania’s economic transition as it approaches EU membership, as well as to develop a modern supplier network. We introduce SCM from a system perspective along three broad areas: input, operations, output and system integration activities. We close by introducing constraints to SCM implementation in Romania. The first major constraint involves a lack of appropriate physical and human capital. Modernization of antiquated equipment and training employees in modern operations practices are prime requisites. The second major constraint, and perhaps the more difficult to change, deals with a lack of social capital among Romanian firms and adapting to appropriate managerial and worker values and attitudes.Supply Chain Management; Social Capital; Transition Economy; Economic Development.

Internet Industry Competition Dynamics: Peering Limitations, Exposure, and Counter Strategies

The Internet industry is vertically integrated with Internet Backbone Providers (IBPs) and Internet Service Providers (ISPs.) Although there are many ISPs and IBPs in each stream, both markets are considered independent oligopolies in that there are a few dominant competitors in each market. It is generally accepted that the Internet industry structure has evolved into a four-tier hierarchical structure. The synergistic and codependent nature of the Internet industry is the key element in understanding the competitive environment in which both IBP’s and ISP’s cooperate. Peering is an efficient way to exchange traffic freely within the access tier, nevertheless competitive constraints limit within tier exchanges. This paper combines the value chain model, competitive force model and a game model to illustrate the interconnection competitive perspective between IBP and ISPs and demonstrate why peering is difficult in the local access market

Wal-Marts Dilemma In The 21st Century: Sales Growth Vs. Inventory Growth

Wal-Mart has been a leader in the retail industry since 1980s. In the 21st century, Wal-Marts RFID initiative is another innovation for Wal-Marts supply chain management. Wal-Marts recent business target in the 21Century is making a higher sales growth rate than inventory growth rate. Comparing with financial ratios of Wal-Marts competitors, Wal-Mart has significantly better ratios for days-in-inventory, inventory-sales-ratio, and cash-conversion-cycle. However, there is no significant evidence of better ratios for supply chain related profit ratio. Regression analysis reveals that while days-in-inventory has a similar effect on both sales growth rate and inventory growth rate, supply chain ratio has more effect on inventory growth rate than sales growth rate