The Susceptibility of Programs to Context Switching

Coordinated Science Laboratory was formerly known as Control Systems LaboratoryNational Science Foundation / MIP-8809478NCR Corp.AMD Corp. 29K Advanced Processor Development DivisionNational Aeronautics and Space Administration / NASA NAG 1-613Office of Naval Research / N00014-88-K-0656Hewlett-Packard Co

Polarization dynamics in vertical-cavity surface emitting lasers

Experiments and their interpretation on polarization dynamics and polarization switching in vertical-cavity surface-emitting lasers operated in the fundamental transverse mode regime are reviewed. Important observations are switching events to a mode with the lower unsaturated gain and the existence of elliptically polarized dynamical transition states after the destabilization of the low-frequency polarization mode. The observations demonstrate the need to consider explicitly the phase properties of the optical field as well as nonlinear effects affecting polarization selection above threshold. Good qualitative agreement is found with a model which takes into account the spin degrees of freedom of the light field as well as of the carriers (`spin-flip model'), if the spin-flip rate is taken to be some tens of $10^9$~s$^{-1}$. This constitutes a strong -- though indirect -- indication that spin dependent processes are important in polarization selection in the devices investigated

Effective food and nutrition policy responses to HIV/AIDS

The impact of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) on people's lives and on development is staggering. Millions have died and livelihoods have been devastated, particularly in Sub-Saharan Africa. Agriculture and natural resources are important components of such livelihoods. And the nutritional status of those infected and affected plays a large part in determining their current welfare and their ability to further develop their livelihoods towards activities that help to mitigate the impacts of AIDS and prevent the spread of HIV. This paper first reviews the potential pathways through which HIV/AIDS affects assets and institutions generally and then the specific impacts on agriculture, natural resource management, food security, and nutrition. The review addresses the question of how the public sector can and should respond to these challenges. The focus is primarily on mitigation, though the authors note that effective mitigation can also serve as a very cost-effective form of prevention. As labor becomes depleted, new cultivation technologies and varieties need to be developed that do not rely so much on labor, yet allow crops to remain drought resistant and nutritious.Sustainable livelihoods. ,HIV/AIDS ,Africa, Sub-Saharan. ,Nutritional status. ,Crops and soil Management. ,HIV/AIDS ,Nutritional status. ,