Browsing by Subject "Population dynamics"

Now showing 1 - 3 of 3

Open Access
Analysis of blood cell production under growth factors switching
(Elsevier B.V., 2017) Djema, W.; Özbay, Hitay; Bonnet, C.; Fridman, E.; Mazenc, F.; Clairambault, J.
Hematopoiesis is a highly complicated biological phenomenon. Improving its mathematical modeling and analysis are essential steps towards consolidating the common knowledge about mechanisms behind blood cells production. On the other hand, trying to deepen the mathematical modeling of this process has a cost and may be highly demanding in terms of mathematical analysis. In this paper, we propose to describe hematopoiesis under growth factor-dependent parameters as a switching system. Thus, we consider that different biological functions involved in hematopoiesis, including aging velocities, are controlled through multiple growth factors. Then we attempt a new approach in the framework of time-delay switching systems, in order to interpret the behavior of the system around its possible positive steady states. We start here with the study of a specific case in which switching is assumed to result from drug infusions. In a broader context, we expect that interpreting cell dynamics using switching systems leads to a good compromise between complexity of realistic models and their mathematical analysis. © 2017
Open Access
Population changes in Ottoman Anatolia during the 16th and 17th centuries: The "demographic crisis" reconsidered
(Cambridge University Press, 2004) Özel, O.
Whatever the fruits of discussing the problem at such a theoretical level, in the case of Anatolia it is perhaps more important to bear in mind the geographical dimension of the population changes in the late-16th- and early-17th-century Ottoman Empire. The crucial question is how representative the cases of demographic pressure in Anatolia described here were as far as the whole empire was concerned. Furthermore, one may ask the same question for Anatolia only, considering the fact that in some parts of Anatolia the population seems to have remained within reasonable limits, although substantial growth in the 16th century was a general phenomenon throughout the Empire. It is therefore imperative to pay attention to voices that emphasize regional differences in terms of demographic changes-differences that depended largely on the quality and quantity of the land, climatic conditions, economic opportunities, and, as Karen Barkey rightly suggests, the patron-client relations at the local level and in the empire in general. It is also clear that population growth does not necessarily or automatically mean "pressure." What this study shows in this respect is that one can speak of such pressure in at least some parts of the empire-in this case, the north-central Anatolian province of Rum. Whether the apparent rise in population resulted in similar pressure elsewhere in Anatolia or throughout the empire toward the end of the century remains a question. Nevertheless, this study has also pointed out that the Celali rebellions and widespread terror in the Anatolian countryside were closely related to the demographic growth of the 16th century.
Open Access
SONIC: streaming overlapping community detection
(Springer, 2016) Sarıyüce, A. E.; Gedik, B.; Jacques-Silva, G.; Wu, Kun-Lung; Catalyurek, U.V.
A community within a graph can be broadly defined as a set of vertices that exhibit high cohesiveness (relatively high number of edges within the set) and low conductance (relatively low number of edges leaving the set). Community detection is a fundamental graph processing analytic that can be applied to several application domains, including social networks. In this context, communities are often overlapping, as a person can be involved in more than one community (e.g., friends, and family); and evolving, since the structure of the network changes. We address the problem of streaming overlapping community detection, where the goal is to maintain communities in the presence of streaming updates. This way, the communities can be updated more efficiently. To this end, we introduce SONIC—a find-and-merge type of community detection algorithm that can efficiently handle streaming updates. SONIC first detects when graph updates yield significant community changes. Upon the detection, it updates the communities via an incremental merge procedure. The SONIC algorithm incorporates two additional techniques to speed-up the incremental merge; min-hashing and inverted indexes. Results show that SONIC can provide high quality overlapping communities, while handling streaming updates several orders of magnitude faster than the alternatives performing from-scratch computation.