Synchronization in Random Geometric Graphs

In this paper we study the synchronization properties of random geometric graphs. We show that the onset of synchronization takes place roughly at the same value of the order parameter that a random graph with the same size and average connectivity. However, the dependence of the order parameter with the coupling strength indicates that the fully synchronized state is more easily attained in random graphs. We next focus on the complete synchronized state and show that this state is less stable for random geometric graphs than for other kinds of complex networks. Finally, a rewiring mechanism is proposed as a way to improve the stability of the fully synchronized state as well as to lower the value of the coupling strength at which it is achieved. Our work has important implications for the synchronization of wireless networks, and should provide valuable insights for the development and deployment of more efficient and robust distributed synchronization protocols for these systems.Comment: 5 pages, 4 figure

Considerations for a design and operations knowledge support system for Space Station Freedom

Engineering and operations of modern engineered systems depend critically upon detailed design and operations knowledge that is accurate and authoritative. A design and operations knowledge support system (DOKSS) is a modern computer-based information system providing knowledge about the creation, evolution, and growth of an engineered system. The purpose of a DOKSS is to provide convenient and effective access to this multifaceted information. The complexity of Space Station Freedom's (SSF's) systems, elements, interfaces, and organizations makes convenient access to design knowledge especially important, when compared to simpler systems. The life cycle length, being 30 or more years, adds a new dimension to space operations, maintenance, and evolution. Provided here is a review and discussion of design knowledge support systems to be delivered and operated as a critical part of the engineered system. A concept of a DOKSS for Space Station Freedom (SSF) is presented. This is followed by a detailed discussion of a DOKSS for the Lyndon B. Johnson Space Center and Work Package-2 portions of SSF

Aging cellular networks: chaperones as major participants

We increasingly rely on the network approach to understand the complexity of cellular functions. Chaperones (heat shock proteins) are key "networkers", which have among their functions to sequester and repair damaged protein. In order to link the network approach and chaperones with the aging process, we first summarize the properties of aging networks suggesting a "weak link theory of aging". This theory suggests that age-related random damage primarily affects the overwhelming majority of the low affinity, transient interactions (weak links) in cellular networks leading to increased noise, destabilization and diversity. These processes may be further amplified by age-specific network remodelling and by the sequestration of weakly linked cellular proteins to protein aggregates of aging cells. Chaperones are weakly linked hubs [i.e., network elements with a large number of connections] and inter-modular bridge elements of protein-protein interaction, signalling and mitochondrial networks. As aging proceeds, the increased overload of damaged proteins is an especially important element contributing to cellular disintegration and destabilization. Additionally, chaperone overload may contribute to the increase of "noise" in aging cells, which leads to an increased stochastic resonance resulting in a deficient discrimination between signals and noise. Chaperone- and other multi-target therapies, which restore the missing weak links in aging cellular networks, may emerge as important anti-aging interventions.Comment: 7 pages, 4 figure

Providing Access to Safe Water: Lessons Learned from Two Decades of Philanthropic Investment in the Rural Poor

The Conrad N. Hilton Foundation has been a leading U.S. funder for increasing safe water access for over 20 years. The author reflects on that history to describe valuable lessons, especially on partnership (in the context of West Africa Water Initiative), and how to think strategically in the long- and short-term about efficient and sustainable WASH funding

Distributed Denial-of-Service Defense System

Distributed denial-of-service (DoS) attacks present a great threat to the Internet, and existing security mechanisms cannot detect or stop them successfully. The problem lies in the distributed nature of attacks, which engages the power of a vast number of coordinated hosts. To mitigate the impacts of DDoS attacks, it is important to develop such defenses system that canbothdetect andreact against ongoing attacks. The attacks ideally should be stopped as close to the sources as possible, saving network resources andreducing congestion. The DDoS defense system that is deployed at the source-end should prevent the machines at associated network from participating in DDoS attacks. The primary objective of this project, which is developing a DDoS defense system, is to provide good service to a victim's legitimate clients during the attack, thus canceling the denial-of-service effect. The scope of study will coverthe aspect of howthe attack detection algorithms work and identify the attack traffic, hence develop appropriate attack responses. As a source-end defense against DDoS attacks, the attack flows can be stopped before they enter the Internet core and before they aggregate with other attack flows. The methodology chosen for this project is the combination of sequential and iterative approaches of the software development process, which comprises of six main phases, which are initial planning phase, requirement definition phase, system design phase, coding and testing phase, implementation phase, and lastly maintenance and support phase. The system used a source router approach, in which the source router serves as a gateway between the source network containing some of the attack nodes and the rest of the Internet, to detectand limitDDoS streams long before they reach the target. This will be covered in the Findings section of the report. TheDiscussion section will be focus more onthe architecture onthe system, which having three important component; observation, rate-limiting and traffic-policing