Global Changes: Facets of Robust Decisions

The aim of this paper is to provide an overview of existing concepts of robustness and to identify promising directions for coping with uncertainty and risks of global changes. Unlike statistical robustness, general decision problems may have rather different facets of robustness. In particular, a key issue is the sensitivity with respect to low-probability catastrophic events. That is, robust decisions in the presence of catastrophic events are fundamentally different from decisions ignoring them. Specifically, proper treatment of extreme catastrophic events requires new sets of feasible decisions, adjusted to risk performance indicators, and new spatial, social and temporal dimensions. The discussion is deliberately kept at a level comprehensible to a broad audience through the use of simple examples that can be extended to rather general models. In fact, these examples often illustrate fragments of models that are being developed at IIASA

Fitness landscape of the cellular automata majority problem: View from the Olympus

In this paper we study cellular automata (CAs) that perform the computational Majority task. This task is a good example of what the phenomenon of emergence in complex systems is. We take an interest in the reasons that make this particular fitness landscape a difficult one. The first goal is to study the landscape as such, and thus it is ideally independent from the actual heuristics used to search the space. However, a second goal is to understand the features a good search technique for this particular problem space should possess. We statistically quantify in various ways the degree of difficulty of searching this landscape. Due to neutrality, investigations based on sampling techniques on the whole landscape are difficult to conduct. So, we go exploring the landscape from the top. Although it has been proved that no CA can perform the task perfectly, several efficient CAs for this task have been found. Exploiting similarities between these CAs and symmetries in the landscape, we define the Olympus landscape which is regarded as the ''heavenly home'' of the best local optima known (blok). Then we measure several properties of this subspace. Although it is easier to find relevant CAs in this subspace than in the overall landscape, there are structural reasons that prevent a searcher from finding overfitted CAs in the Olympus. Finally, we study dynamics and performance of genetic algorithms on the Olympus in order to confirm our analysis and to find efficient CAs for the Majority problem with low computational cost

Activation of RhoA and ROCK Are Essential for Detachment of Migrating Leukocytesh

Detachment of the rear of the cell from its substratum is an important aspect of locomotion. The signaling routes involved in this adhesive release are largely unknown. One of the few candidate proteins to play a role is RhoA, because activation of RhoA in many cell types leads to contraction, a mechanism probably involved in detachment. To study the role of RhoA in detachment regulation, we analyzed several subsets of expert migratory leukocytes by video microscopy. In contrast to fast-migrating neutrophils, eosinophils do not detach the rear of the cell unless stimulated with serum. When measuring the amount of active RhoA, with the use of a GSTRhotekin pulldown assay, we found that serum is an excellent activator of RhoA in granulocytes. Inhibition of RhoA or one of Rhos target proteins, the kinase ROCK, in neutrophils leads to the phenotype seen in eosinophils: the rear of the cell is firmly attached to the substratum, whereas the cell body is highly motile. ROCK-inhibition leads to impaired migration of granulocytes in filters, on glass, and through endothelial monolayers. Also, the ROCK signaling pathway is involved in changes of integrin-mediated adhesion. Eosinophil transduction by a tat-fusion construct containing active RhoA resulted in detachment stimulation in the presence of chemoattractant. From these results we conclude that activation of the RhoA-ROCK pathway is essential for detachment of migratory leukocytes

Acid Rain Abatement in Europe: Two Progress Reports

The first report describes briefly the RAINS (Regional Acidification Information and Simulation) model and presents three alternative abatement strategies for acidification in Europe. These alternatives are: a percentage reduction of emissions per country, reductions based on indicators and targetted emission reductions. In the second report the fact that 20 European countries have stated that they will reduce their sulfur dioxide emissions by at least 30% in the years 1993-1995 based on 1980 emissions is discussed. Some countries will reduce more, e.g. France by 50%. Although politically this is an important step, a more or less flat rate of emission reduction throughout Europe is not an efficient solution. This paper describes an alternate emission reduction targetted to those areas where depositions are high and taking into account the source-receptor relationships in Europe. The reductions are calculated by using the model RAINS which is being developed at IIASA. RAINS is a set of linked submodels dealing with energy scenarios, sulfur dioxide emissions, abatement options, long-range transport, deposition, forest soil acidification and lake acidification. For the purpose of this paper an optimization algorithm developed by R. Shaw and J. Young (AES, Canada) has been connected with RAINS. The results show optimal reduction patterns in Europe for a number of different receptor areas and alternative energy scenarios

An analysis of the environmental pressure exerted by the eucalyptus-based Kraft pulp industry in Thailand

The study reported here focuses on the environmental pressure exerted by large-scale eucalyptus-based kraft pulp industry in Thailand. The objective of this study was to identify the most important sources of greenhouse gases, acidifying and eutrophying compounds and tropospheric ozone precursors, human toxicity compounds and solid waste associated with the kraft pulp industry. To this end, we performed an environmental systems analysis of the kraft pulp industry system in which we distinguished between two subsystems: the eucalyptus forestry subsystem and the kraft pulp production subsystem. The results indicate that the environmental pressure is caused by the kraft pulp production subsystem rather than by the eucalyptus forestry one. The chemical recovery unit was found to be the most important source of carbon dioxide (CO2) and sulfur dioxide (SO2) and responsible for more than one-half of the emissions of greenhouse gases and acidifying compounds from eucalyptus-based kraft pulp production in Thailand. Biomass combustion in the energy gene ration unit is an important source of nitrogen oxide (NOx) and carbon monoxide (CO) which in turn are responsible for over 50% of the emissions of tropospheric ozone precursors. About 73% of the eutrophication is caused by biological aerobic wastewater treatment emitting phosphorus (P). With respect to the eucalyptus forestry, only fertilizer use in eucalyptus plantations is a relevant source of pollution through the emission of nitrous oxide (N2O) and phosphate (PO4 3-)

On RAF Sets and Autocatalytic Cycles in Random Reaction Networks

The emergence of autocatalytic sets of molecules seems to have played an important role in the origin of life context. Although the possibility to reproduce this emergence in laboratory has received considerable attention, this is still far from being achieved. In order to unravel some key properties enabling the emergence of structures potentially able to sustain their own existence and growth, in this work we investigate the probability to observe them in ensembles of random catalytic reaction networks characterized by different structural properties. From the point of view of network topology, an autocatalytic set have been defined either in term of strongly connected components (SCCs) or as reflexively autocatalytic and food-generated sets (RAFs). We observe that the average level of catalysis differently affects the probability to observe a SCC or a RAF, highlighting the existence of a region where the former can be observed, whereas the latter cannot. This parameter also affects the composition of the RAF, which can be further characterized into linear structures, autocatalysis or SCCs. Interestingly, we show that the different network topology (uniform as opposed to power-law catalysis systems) does not have a significantly divergent impact on SCCs and RAFs appearance, whereas the proportion between cleavages and condensations seems instead to play a role. A major factor that limits the probability of RAF appearance and that may explain some of the difficulties encountered in laboratory seems to be the presence of molecules which can accumulate without being substrate or catalyst of any reaction.Comment: pp 113-12