PDF version This talk explores three concepts of system in engineering: systems theory, systems approach, and systems engineering. They are exemplified in three dimensions of engineering: science, design, and management. Unifying the three system concepts is the idea of function: functional abstraction in theory, functional analysis in design, and functional requirements in management. Signifying what a system is for, function is a purposive notion absent in physical science, which aims to understand nature. It is prominent in engineering, which aims to (...) transform nature for serving the wants and needs of people. (shrink)

Several key areas in modeling the cardiovascular and respiratory control systems are reviewed and examples are given which reflect the research state of the art in these areas. Attention is given to the interrelated issues of data collection, experimental design, and model application including model development and analysis. Examples are given of current clinical problems which can be examined via modeling, and important issues related to model adaptation to the clinical setting.

Possible effects of interaction (cross-talk) between signaling pathways is studied in a system of Reaction–Diffusion (RD) equations. Furthermore, the relevance of spontaneous neurite symmetry breaking and Turing instability has been examined through numerical simulations. The interaction between Retinoic Acid (RA) and Notch signaling pathways is considered as a perturbation to RD system of axon-forming potential for N2a neuroblastoma cells. The present work suggests that large increases to the level of RA–Notch interaction can possibly have substantial impacts on neurite outgrowth and (...) on the process of axon formation. This can be observed by the numerical study of the homogeneous system showing that in the absence of RA–Notch interaction the unperturbed homogeneous system may exhibit different saddle-node bifurcations that are robust under small perturbations by low levels of RA–Notch interactions, while large increases in the level of RA–Notch interaction result in a number of transitions of saddle-node bifurcations into Hopf bifurcations. It is speculated that near a Hopf bifurcation, the regulations between the positive and negative feedbacks change in such a way that spontaneous symmetry breaking takes place only when transport of activated Notch protein takes place at a faster rate. (shrink)

Recently improved understanding of evolutionary processes suggests that tree-based phylogenetic analyses of evolutionary change cannot adequately explain the divergent evolutionary histories of a great many genes and gene complexes. In particular, genetic diversity in the genomes of prokaryotes, phages, and plasmids cannot be fit into classic tree-like models of evolution. These findings entail the need for fundamental reform of our understanding of molecular evolution and the need to devise alternative apparatus for integrated analysis of these genomes. We advocate the development (...) of integrative phylogenomics for analyzing these genomes and their histories, with tools suited to analyzing the importance of lateral gene transfer (LGT) and of DNA evolution in extra-cellular mobile genetic elements (e.g., viruses, plasmids). These phenomena greatly increase the complexity of relationships among interacting genetic partners, as they exchange functional genetic units. We examine the ontology of functional genetic units, interacting genetic partners, and emergent genetic associations, argue that these three categories of entities are required for a successful integrated phylogenomics. We conclude with arguments to suggest that the proposed new perspective and associated tools are suitable, and perhaps required, as a replacement for the bifurcating trees that have dominated evolutionary thinking for the last 150 years. (shrink)

The levels that compose biological hierarchies each have their own energetic, spatial and temporal structure. Indeed, it is the discontinuity in energy relationships between levels, as well as the similarity of sub-systems that support them, that permits levels to be defined. In this paper, the temporal structure of living hierarchies, in particular that pertaining to Human society, is examined. Consideration is given to the period defining the lifespan of entities at each level and to a periodic event considered fundamental to (...) the maintenance of that level. The ratio between the duration of these two periods is found to be approximately 2.5 × 104. A similar relationship is found when lower, non-living levels of molecules and atoms are considered. This suggests that there is a constant factor of amplification between analogous periodic events at successive levels of the Human hierarchy. (shrink)

My paper draws on examples from molecular biology, the details of which I have developed elsewhere (Rheinberger 1992, 1993, 1995, 1997). Here, I can give only a brief outline of my argument. Reduction of complexity is a prerequisite for experimental research. To make sense of the universe of living beings, the modern biologist is bound to divide his world into fragments in which parameters can be defined, quantities measured, qualities identified. Such is the nature of any "experimental system." Ontic complexity (...) has to be reduced in order to make experimental research possible. The complexity of the research object, however, is epistemically retained in the rich context of an experimental landscape, where the eruption of "volcanic systems" can change the scenery dramatically as the result of particular, unprecedented findings. (shrink)

Coordination of immune responses in the gut is a complex task. In order to fight pathogens and maintain a defined population of commensal microbes, the mucosal immune system has to coordinate information from the external (luminal) and internal (abluminal) environment and respond accordingly. Dendritic cells (DCs) are crucial cell types involved in this process as they integrate these signals and direct immunogenic or tolerogenic responses. Here, we review how various functions of DCs depend on microbial stimuli and how these stimuli (...) influence the course of immune activation. (shrink)