TDRSS momentum unload planning

A knowledge-based system is described which monitors TDRSS telemetry for problems in the momentum unload procedure. The system displays TDRSS telemetry and commands in real time via X-windows. The system constructs a momentum unload plan which agrees with the preferences of the attitude control specialists and the momentum growth characteristics of the individual spacecraft. During the execution of the plan, the system monitors the progress of the procedure and watches for unexpected problems

Noise Reduction by Diffusional Dissipation in a Minimal Quorum Sensing Motif

Cellular interactions are subject to random fluctuations (noise) in quantities of interacting molecules. Noise presents a major challenge for the robust function of natural and engineered cellular networks. Past studies have analyzed how noise is regulated at the intracellular level. Cell–cell communication, however, may provide a complementary strategy to achieve robust gene expression by enabling the coupling of a cell with its environment and other cells. To gain insight into this issue, we have examined noise regulation by quorum sensing (QS), a mechanism by which many bacteria communicate through production and sensing of small diffusible signals. Using a stochastic model, we analyze a minimal QS motif in Gram-negative bacteria. Our analysis shows that diffusion of the QS signal, together with fast turnover of its transcriptional regulator, attenuates low-frequency components of extrinsic noise. We term this unique mechanism “diffusional dissipation” to emphasize the importance of fast signal turnover (or dissipation) by diffusion. We further show that this noise attenuation is a property of a more generic regulatory motif, of which QS is an implementation. Our results suggest that, in a QS system, an unstable transcriptional regulator may be favored for regulating expression of costly proteins that generate public goods

The Effect of Carbon Credits on Savanna Land Management and Priorities for Biodiversity Conservation

Carbon finance offers the potential to change land management and conservation planning priorities. We develop a novel approach to planning for improved land management to conserve biodiversity while utilizing potential revenue from carbon biosequestration. We apply our approach in northern Australia's tropical savanna, a region of global significance for biodiversity and carbon storage, both of which are threatened by current fire and grazing regimes. Our approach aims to identify priority locations for protecting species and vegetation communities by retaining existing vegetation and managing fire and grazing regimes at a minimum cost. We explore the impact of accounting for potential carbon revenue (using a carbon price of US$14 per tonne of carbon dioxide equivalent) on priority areas for conservation and the impact of explicitly protecting carbon stocks in addition to biodiversity. Our results show that improved management can potentially raise approximately US$5 per hectare per year in carbon revenue and prevent the release of 1–2 billion tonnes of carbon dioxide equivalent over approximately 90 years. This revenue could be used to reduce the costs of improved land management by three quarters or double the number of biodiversity targets achieved and meet carbon storage targets for the same cost. These results are based on generalised cost and carbon data; more comprehensive applications will rely on fine scale, site-specific data and a supportive policy environment. Our research illustrates that the duel objective of conserving biodiversity and reducing the release of greenhouse gases offers important opportunities for cost-effective land management investments

TDRSS Momentum Unload Planning

We describe a knowledge-based system which monitors TDRSS telemetry for problems in the momentum unload procedure. The system displays TDRSS telemetry and commands in real time via X-Windows. The system constructs a momentum unload plan which agrees with the preferences of the attitude control specialists and the momentum growth characteristics of the individual spacecraft. During the execution of the plan, the system monitors the progress of the procedure and watches for unexpected problems. 1 Introduction This paper describes a knowledge-based system to assist in the operation of the White Sands Ground Terminal (WSGT) for the Tracking, Data and Relay Satellite System (TDRSS). We first review knowledge-based systems that have been developed in support of spacecraft operations. We also review the specific systems previously developed in the context of TDRSS operations. Since our system acts as an assistant in the planning and execution of TDRSS momentum unloads, we present some backgr..

Migrant Remittances, Population Ageing and Intergenerational Family Obligations in Sri Lanka

As Sri Lanka’s population ages, its migrant women face a difficult choice: should they work abroad to remit money to provision their families, or should they stay at home to look after elderly kin? Although numerous studies have explored migration’s effects on children, fewer works focus on issues of elder care. This essay presents contextualizing information on transnational migration from Sri Lanka and the rapid ageing that is transforming the country’s population structure from a pyramid with many youth and few elders into a column. Using qualitative ethnographic data gathered from a labour-sending village in southern Sri Lanka, this anthropological essay considers social priorities around remittances and intergenerational family obligations for care work. Villagers make decisions about allocating able-bodied family members’ labour based on key concepts of filial duty, combined with an analysis of a family’s financial and social resources and the vulnerabilities of its members based on their gender and age. Critiquing assumptions about elders’ lack of economic activity, the essay notes their key role in facilitating labour migration. The data reveal the importance of gender roles, educational achievements, and generational shifts in evaluating emerging practices. In the future, intergenerational family obligations to mutual care will persist despite population aging. But as extended families shrink and care work grows more demanding, choices between elder care and migrant remittances will become more challenging