Dependence of Nebular Heavy-Element Abundance on H I Content for Spiral Galaxies

We analyze the galactic H I content and nebular log(O/H) for 60 spiral galaxies in the Moustakas et al. (2006) spectral catalog. After correcting for the mass-metallicity relationship, we show that the spirals in cluster environments show a positive correlation for log(O/H) on DEF, the galactic H I deficiency parameter, extending the results of previous analyses of the Virgo and Pegasus I clusters. Additionally, we show for the first time that galaxies in the field obey a similar dependence. The observed relationship between H I deficiency and galactic metallicity resembles similar trends shown by cosmological simulations of galaxy formation including inflows and outflows. These results indicate the previously observed metallicity-DEF correlation has a more universal interpretation than simply a cluster's effects on its member galaxies. Rather, we observe in all environments the stochastic effects of metal-poor infall as minor mergers and accretion help to build giant spirals.Comment: Accepted for publication in Ap

Secure migration of virtual SDN topologies

International audienceWith the emergence of Software Defined Networks (SDN), new virtualization techniques have appeared (e.g., FlowVi-sor [14]). Traditional hypervision has attracted a lot of attention with respect to resource sharing and multi-tenancy. Cloud providers have usually a solid knowledge on how to manage computing , memory and storage resources, but often lack the ability to properly manage network resources. Thanks to OpenFlow, a widespread SDN southbound interface protocol, virtualizing the network infrastructure has become possible. However, network virtualization also comes with its own security issues ([5], [6]). In this paper, we focus on the security aspects related to the migration of virtual networks. After providing a brief overview of the technological scope of our work, we review the state of the art of the migration of virtual resources. Finally, we conclude with our current results and the prospective outcomes we expect to obtain

Designing security-aware service requests for NFV-enabled networks

International audienceNetwork Function Virtualization (NFV) is a new concept where virtualization is used to shift "network functions" (e.g., routers, switches, load-balancers, proxies) from specialized hardware appliances to software images running on high volume servers. The resource allocation problem in the NFV environment has received considerable attention in the past years. However, little attention was paid to the security aspects of the problem in spite of the increasing number of vulnerabilities faced by cloud-based applications. Securing the services is an urgent need to completely benefit from the advantages offered by NFV. In this paper, we show how a network service request, composed of a set of service function chains (SFC) should be modified and enriched to take into consideration the security requirements of the supported service. We examine the well-known security best practices and propose a two-step algorithm that extends the initial SFC requests to a more complex chaining model that includes the security requirements of the service

In Praise of Investor Irrationality

How should a market filled with investors who chronically make bad investments, but is nevertheless efficient, be regulated? A growing body of evidence suggests that this is the state of most securities markets; investors rely on cognitive processes that produce systematically bad choices, and yet the market remains largely efficient. In fact, cognitive errors might be essential to their efficient operation. Even investors who make systematic errors also often possess real and unique information that can contribute to accurate pricing of securities. If such investors became mindful of their limited ability to distinguish between real information and erroneous information, they would decline to rely on their beliefs to invest and would thereby withhold private information from the market. Over-confidence on the part of these investors leads them to trade anyway. This over-confidence provides market liquidity, but more importantly, provides the market with the private information that individual investors possess (but should, rationally, withhold). Hence, reforms designed to save investors from the costs of their cognitive errors would reduce market liquidity and deprive the market of valuable information. In short, markets need irrationality

In Praise of Investor Irrationality

How should a market filled with investors who chronically make bad investments, but is nevertheless efficient, be regulated? A growing body of evidence suggests that this is the state of most securities markets; investors rely on cognitive processes that produce systematically bad choices, and yet the market remains largely efficient. In fact, cognitive errors might be essential to their efficient operation. Even investors who make systematic errors also often possess real and unique information that can contribute to accurate pricing of securities. If such investors became mindful of their limited ability to distinguish between real information and erroneous information, they would decline to rely on their beliefs to invest and would thereby withhold private information from the market. Over-confidence on the part of these investors leads them to trade anyway. This over-confidence provides market liquidity, but more importantly, provides the market with the private information that individual investors possess (but should, rationally, withhold). Hence, reforms designed to save investors from the costs of their cognitive errors would reduce market liquidity and deprive the market of valuable information. In short, markets need irrationality

Optimizing resource allocation for secure SDN-based virtual network migration

International audienceRecent evolutions in cloud infrastructures allowed service providers to tailor new services for demanding customers. Providing these services confronts the infrastructure providers with costs and constraints considerations. In particular, security constraints are a major concern for today's businesses as the leak of personal information would tarnish their reputation. Recent works provide examples on how an attacker may leverage the infrastructure's weaknesses to steal sensitive information from the users. Specifically, an attacker can leverage maintenance processes inside the infrastructure to conduct an attack. In this paper, we consider the migration of a virtual network as the maintenance process. Then we determine the optimal monitoring resources allocation in this context with a Markov Decision Process. This model takes into account the impact of monitoring the infrastructure, the migration process and finally how the attacker may chose particular targets in the infrastructure. We provide a working prototype implemented in Python

Combining Technical and Financial Impacts for Countermeasure Selection

Research in information security has generally focused on providing a comprehensive interpretation of threats, vulnerabilities, and attacks, in particular to evaluate their danger and prioritize responses accordingly. Most of the current approaches propose advanced techniques to detect intrusions and complex attacks but few of these approaches propose well defined methodologies to react against a given attack. In this paper, we propose a novel and systematic method to select security countermeasures from a pool of candidates, by ranking them based on the technical and financial impact associated to each alternative. The method includes industrial evaluation and simulations of the impact associated to a given security measure which allows to compute the return on response investment for different candidates. A simple case study is proposed at the end of the paper to show the applicability of the model.Comment: In Proceedings AIDP 2014, arXiv:1410.322

The contribution of hydrogen to the corrosion of 2024 aluminium alloy exposed to thermal and environmental cycling in chloride media

This work is focused on the role of hydrogen in corrosion damage induced by the cyclic exposure of 2024 aluminium alloy to chloride media with air emersion periods at room and/or negative temperatures. Various analysis and microscopic observation techniques were applied at intergranular corrosion defects. A mechanism involving the contribution of hydrogen to the degradation of the alloy mechanical properties is presented. Several consecutive stress states appear during cycling, resulting from volume expansion of the electrolyte trapped in the intergranular defects during emersion phases at -20°C. These stress states lead to hydrogen diffusion, transport and trapping