Dust Formation in the Ejecta of Common Envelope Systems

The material that is ejected in a common-envelope (CE) phase in a close binary system provides an ideal environment for dust formation. By constructing a simple toy model to describe the evolution of the density and the temperature of CE ejecta and using the \emph{AGBDUST} code to model dust formation, we show that dust can form efficiently in this environment. The actual dust masses produced in the CE ejecta depend strongly on their temperature and density evolution. We estimate the total dust masses produced by CE evolution by means of a population synthesis code and show that, compared to dust production in AGB stars, the dust produced in CE ejecta may be quite significant and could even dominate under certain circumstances.Comment: 11pages, 7 figures, accepted for publication by Ap

Towards a Unified Radio Power Management Architecture for Wireless Sensor Networks

In many wireless sensor networks, energy is an extremely limited resource. While many different power management strategies have been proposed to help reduce the amount of energy wasted, application developers still face two fundamental challenges when developing systems with stringent power constraints. First, existing power management strategies are usually tightly coupled with network protocols and other system functionality. This monolithic approach has led to standalone solutions that cannot easily be reused or extended to other applications or platforms. Second, different power management strategies make different and sometimes even conflicting assumptions about the rest of the system with which they need to interact. Without knowledge of which strategies are interoperable with which set of network stack protocols it is dificult for application developers to make informed decisions as to which strategy is most appropriate for their particular application. To address these challenges, we propose a Unified Power Management Architecture (UPMA) that supports the flexible composition of different power management strategies based on application requirements. We envision this architecture to consist of both low level programming interfaces, as well as high level modeling abstractions. These abstractions characterize the key properties of different applications, network protocols, and power management strategies. Using these properties, configuration tools can be created that match each application with the most appropriate network protocol and power management strategy suited to its needs

Link Layer Support for Unified Radio Power Management In Wireless Sensor Networks

Radio power management is of paramount concern in wireless sensor networks that must achieve long lifetimes on scarce amounts of energy. While a multitude of power management protocols have been proposed in the past, the lack of system support for flexibly integrating them with a diverse set of applications and network platforms has made them difficult to use. Instead of proposing yet another power management protocol, this paper focuses on providing link layer support towards realizing a Unified Power Management Architecture (UPMA) for flexible radio power management in wireless sensor networks. In contrast to the monolithic approaches adopted by existing power management solutions, we provide (1) a set of standard interfaces that allow different power management protocols existing at the link layer to be easily implemented on top of common MAC level functionality, (2) an architectural framework for enabling these protocols to be easily swapped in and out depending on the needs of the applications that require them, and (3) a mechanism for coordinating the existence of multiple applications, each of which may have different requirements for the same underlying power management protocol. We have implemented these features on the Mica2 and Telosb radio stacks in TinyOS-2.0. Microbenchmark results demonstrate that the separation of power management from MAC level functionality incurs a negligible decrease in performance when compared to existing monolithic implementations. Two case studies show that the power management requirements of multiple applications can be easily coordinated, sometimes even resulting in better power savings than any one of them can achieve individually

A Unified Architecture for Flexible Radio Power Management in Wireless Sensor Networks

A challenge for many wireless sensor networks is to remain operational for long periods of time on a very limited power supply. While many power management protocols have been proposed, a solution does not yet exist that allows them to be seamlessly integrated into the existing systems. In this paper we study the architectural support required to resolve this issue. We propose a framework that separates sleep scheduling from the basic MAC layer functionality and provide a set of unified interfaces between them. This framework enables different sleep scheduling policies to be easily implemented on top of multiple MAC layers. Such a flexibility allows applications to choose the best sleep scheduling policy based on their own particular needs. We demonstrate the practicality of our approach by implementing this framework on top of both the mica2 and telosb radio stacks in TinyOS 2.0. Our micro-benchmark results show that at the cost of a slight increase in code size, our framework significantly eases the development of new radio power management protocols across multiple WSN platform

Localized and Configurable Topology Control in Lossy Wireless Sensor Networks

Recent empirical studies revealed that multi-hop wireless networks like wireless sensor networks and 802.11 mesh networks are inherently lossy. This finding introduces important new challenges for topology control. Existing topology control schemes often aim at maintaining network connectivity that cannot guarantee satisfactory path quality and communication performance when underlying links are lossy. In this paper, we present a localized algorithm, called Configurable Topology Control (CTC), that can configure a network topology to different provable quality levels (quantified by worst-case dilation bounds in terms of expected total number of transmisssions) required by applications. Each node running CTC computes its transmission power solely based on the link quality information collected within its local neighborhood and does not assume that the neighbor locations or communication ranges are known. Our simulations based on a realistic radio model of Mica2 motes show that CTC yields configurable communication performance and outperforms existing topology control algorithms that do not account for lossy links