A Survey on Continuous Time Computations

We provide an overview of theories of continuous time computation. These theories allow us to understand both the hardness of questions related to continuous time dynamical systems and the computational power of continuous time analog models. We survey the existing models, summarizing results, and point to relevant references in the literature

Computability and dynamical systems

In this paper we explore results that establish a link between dynamical systems and computability theory (not numerical analysis). In the last few decades, computers have increasingly been used as simulation tools for gaining insight into dynamical behavior. However, due to the presence of errors inherent in such numerical simulations, with few exceptions, computers have not been used for the nobler task of proving mathematical results. Nevertheless, there have been some recent developments in the latter direction. Here we introduce some of the ideas and techniques used so far, and suggest some lines of research for further work on this fascinating topic

Systems Perspectives on the Interaction Between Human and Technological Resources

Peer reviewe

Sequence of Physical Changes to the Cell Membrane During Glucocorticoid-Induced Apoptosis in S49 Lymphoma Cells

During apoptosis, physical changes in the plasma membrane prepare the cell for clearance by phagocytes and hydrolysis by secretory phospholipase A2 (sPLA2). The relationships among these changes have not been adequately established, especially for hormone-stimulated apoptosis. This study addresses these issues for glucocorticoid-induced apoptosis in S49 lymphoma cells. Flow cytometry, microscopy, and fluorescence spectroscopy were used to assess merocyanine 540 emission, laurdan generalized polarization, phosphatidylserine exposure, caspase activation, and membrane permeability to propidium iodide in the absence and presence of sPLA2. The earliest event observed was activation of cellular caspases. Results with membrane probes suggest that interlipid spacing also increases early during apoptosis and precedes transbilayer migration of phosphatidylserine, DNA fragmentation, and a general increase in lipid order associated with blebbing and dissolution of the cells. The activity of sPLA2 appeared to be linked more to lipid spacing than to loss of membrane asymmetry. The early nature of some of these events and their ability to promote activity of a proinflammatory enzyme suggests the possibility of an inflammatory response during T-lymphocyte apoptosis