Carleton University

About: Carleton University is a education organization based out in Ottawa, Ontario, Canada. It is known for research contribution in the topics: Population & Context (language use). The organization has 15852 authors who have published 39650 publications receiving 1106610 citations.

Energy-Efficient Resource Allocation for Heterogeneous Cognitive Radio Networks with Femtocells

Abstract: Both cognitive radio and femtocell have been considered as promising techniques in wireless networks. However, most of previous works are focused on spectrum sharing and interference avoidance, and the energy efficiency aspect is largely ignored. In this paper, we study the energy efficiency aspect of spectrum sharing and power allocation in heterogeneous cognitive radio networks with femtocells. To fully exploit the cognitive capability, we consider a wireless network architecture in which both the macrocell and the femtocell have the cognitive capability. We formulate the energy-efficient resource allocation problem in heterogeneous cognitive radio networks with femtocells as a Stackelberg game. A gradient based iteration algorithm is proposed to obtain the Stackelberg equilibrium solution to the energy-efficient resource allocation problem. Simulation results are presented to demonstrate the Stackelberg equilibrium is obtained by the proposed iteration algorithm and energy efficiency can be improved significantly in the proposed scheme.

Use case maps as architectural entities for complex systems

Abstract: The paper presents a novel, scenario based notation called Use Case Maps (UCMs) for describing, in a high level way, how the organizational structure of a complex system and the emergent behavior of the system are intertwined. The notation is not a behavior specification technique in the ordinary sense, but a notation for helping a person to visualize, think about, and explain the big picture. UCMs are presented as "architectural entities" that help a person stand back from the details during all phases of system development. The notation has been thoroughly exercised on systems of industrial scale and complexity and the distilled essence of what has been found to work in practice is summarized. Examples are presented that confront difficult complex system issues directly: decentralized control, concurrency, failure, diversity, elusiveness and fluidity of runtime views of software, self modification of system makeup, difficulty of seeing large scale units of emergent behavior cutting across systems as coherent entities (and of seeing how such entities arise from the collective efforts of components), and large scale.

Antioxidant defenses and metabolic depression. The hypothesis of preparation for oxidative stress in land snails

Abstract: The roles of enzymatic antioxidant defenses in the natural tolerance of environmental stresses that impose changes in oxygen availability and oxygen consumption on animals is discussed with a particular focus on the biochemistry of estivation and metabolic depression in pulmonate land snails. Despite reduced oxygen consumption and PO2 during estivation, which should also mean reduced production of oxyradicals, the activities of antioxidant enzymes, such as superoxide dismutase and catalase, increased in 30 day-estivating snails. This appears to be an adaptation that allows the snails to deal with oxidative stress that takes place during arousal when PO2 and oxygen consumption rise rapidly. Indeed, oxidative stress was indicated by increased levels of lipid peroxidation damage products accumulating in hepatopancreas within minutes after arousal was initiated. The various metabolic sites responsible for free radical generation during arousal are still unknown but it seems unlikely that the enzyme xanthine oxidase plays any substantial role in this despite being implicated in oxidative stress in mammalian models of ischemia/reperfusion. We propose that the activation of antioxidant defenses in the organs of Otala lactea during estivation is a preparative mechanism against oxidative stress during arousal. Increased activities of antioxidant enzymes have also observed under other stress situations in which the actual production of oxyradicals should decrease. For example, antioxidant defenses are enhanced during anoxia exposure in garter snakes Thamnophis sirtalis parietalis (10 h at 5°C) and leopard frogs Rana pipiens (30 h at 5°C) and during freezing exposure (an ischemic condition due to plasma freezing) in T. sirtalis parietalis and wood frogs Rana sylvatica. It seems that enhancement of antioxidant enzymes during either anoxia or freezing is used as a preparatory mechanism to deal with a physiological oxidative stress that occurs rapidly within the early minutes of recovery during reoxygenation or thawing. Thus, a wide range of stress tolerant animals display coordinated changes in antioxidant defenses that allow them to deal with oxidative stress that occurs as part of natural cycles of stress/recovery that alter oxygen levels in tissues. The molecular mechanisms that trigger and regulate changes in antioxidant enzyme activities in these species are still unknown but could prove to have key relevance for the development of new intervention strategies in the treatment of cardiovascular ischemia/reperfusion injuries in humans.