Quantitative modelling of the human–Earth System a new kind of science?

The five grand challenges set out for Earth System Science by the International Council for Science in 2010 require a true fusion of social science, economics and natural science—a fusion that has not yet been achieved. In this paper we propose that constructing quantitative models of the dynamics of the human–Earth system can serve as a catalyst for this fusion. We confront well-known objections to modelling societal dynamics by drawing lessons from the development of natural science over the last four centuries and applying them to social and economic science. First, we pose three questions that require real integration of the three fields of science. They concern the coupling of physical planetary boundaries via social processes; the extension of the concept of planetary boundaries to the human–Earth System; and the possibly self-defeating nature of the United Nation’s Millennium Development Goals. Second, we ask whether there are regularities or ‘attractors’ in the human–Earth System analogous to those that prompted the search for laws of nature. We nominate some candidates and discuss why we should observe them given that human actors with foresight and intentionality play a fundamental role in the human–Earth System. We conclude that, at sufficiently large time and space scales, social processes are predictable in some sense. Third, we canvass some essential mathematical techniques that this research fusion must incorporate, and we ask what kind of data would be needed to validate or falsify our models. Finally, we briefly review the state of the art in quantitative modelling of the human–Earth System today and highlight a gap between so-called integrated assessment models applied at regional and global scale, which could be filled by a new scale of model

Fairness-oriented overlay VPN topology construction

An important issue in dynamically constructed Virtual Private Networks (VPN) is how the overlay topology is created and maintained. Classical VPN topologies, such as hub-and-spoke or full-mesh, fail to remain convenient and viable when the number of nodes grows to as little as a few tens. Convenient topology formation mechanisms should be distributed, should permit incremental and dynamic operations, and should limit the number of nodes a new entry connects with. In this work, we show that approaches devised to create “short” networks, while yielding a significant total network throughput, may be severely affected by unfairness issues, i.e., different pair of nodes may experience a widely different throughput performance. Hence, we introduce a fairness-oriented topology formation algorithm for VPN. The proposed algorithm is incremental, meaning that the addition of a new node to the overlay topology does not imply rewiring of already established overlay links. Simulation results show that our proposed approach achieves high fairness levels, as quantified in terms of well known Jain's fairness index, meanwhile retaining satisfactory throughput performance

Dene Hunting Organization in Fort Good Hope, Northwest Territories: “Ways We Help Each Other and Share What We Can”

Social inquiry into hunting dynamics in northern indigenous communities in Canada has tended to focus on hunting individually or in small kinship groups, although the role of more formal community hunts is increasingly recognized. Descriptive data are limited, however, on the mechanisms by which foods harvested on such hunts are shared out. This paper considers whether or not the dynamics of sharing meat differed between a community hunt (September 2009) and a series of household-organized hunts (November 2009) in the K’asho Got’ine Dene community of Fort Good Hope (Radilih Koe), Northwest Territories. We consider how sharing might differ in terms of interactions initiated by a request from a recipient (discussed in other literature as “demand sharing”), versus those initiated by a harvester (“giving”). Results reveal that the number of sharing interactions was similar in each case and represented a substantial portion of the total harvest, but the greater number of requests for meat after the community hunt indicates there was more pressure on the community harvesters’ supply than on household hunters’ supply. At the same time, requests were made especially by elders and those in need, reflecting complex norms of resource management and flexible social networks. This study affirms the continued relevance of Dene norms of sharing within contemporary communities and increases our knowledge of the social dimension of community-based resource management.De manière générale, l’étude sociale de la dynamique de la chasse dans les collectivités indigènes du nord du Canada porte principalement sur la chasse individuelle ou en petits groupes composés de personnes apparentées, bien que le rôle de la chasse communautaire davantage organisée soit de plus en plus reconnu. Il existe toutefois peu de données descriptives sur les mécanismes en vertu desquels la nourriture recueillie dans le cadre de la chasse est partagée. La présente communication tente d’établir si la dynamique du partage de la viande diffère ou non entre une chasse communautaire (septembre 2009) et une série de chasses organisées par des ménages (novembre 2009) au sein de la collectivité dénée K’asho Got’ine de Fort Good Hope (Radilih Koe), dans les Territoires du Nord-Ouest. Nous examinons en quoi le partage peut différer sur le plan des interactions déclenchées par un receveur (que l’on nomme « partager sur demande » dans d’autres documents), par opposition aux interactions déclenchées par un récolteur (« donner »). Les résultats ont révélé que le nombre d’interactions de partage était semblable dans chaque cas, et qu’elles représentaient une portion substantielle de la récolte totale, mais que le plus grand nombre de demandes de viande après la chasse communautaire indique qu’il y avait plus de pressions sur l’approvisionnement des récolteurs communautaires que sur l’approvisionnement des chasseurs faisant partie des ménages. Par la même occasion, les aînés et les personnes dans le besoin avaient fait des demandes particulières, ce qui illustre les normes complexes de la gestion des ressources et la souplesse des réseaux sociaux. Cette étude affirme la pertinence continue des normes de partage des Dénés au sein des collectivités contemporaines et enrichit nos connaissances de la dimension sociale de la gestion communautaire des ressources

Theory of Interface: Category Theory, Directed Networks and Evolution of Biological Networks

Biological networks have two modes. The first mode is static: a network is a passage on which something flows. The second mode is dynamic: a network is a pattern constructed by gluing functions of entities constituting the network. In this paper, first we discuss that these two modes can be associated with the category theoretic duality (adjunction) and derive a natural network structure (a path notion) for each mode by appealing to the category theoretic universality. The path notion corresponding to the static mode is just the usual directed path. The path notion for the dynamic mode is called lateral path which is the alternating path considered on the set of arcs. Their general functionalities in a network are transport and coherence, respectively. Second, we introduce a betweenness centrality of arcs for each mode and see how the two modes are embedded in various real biological network data. We find that there is a trade-off relationship between the two centralities: if the value of one is large then the value of the other is small. This can be seen as a kind of division of labor in a network into transport on the network and coherence of the network. Finally, we propose an optimization model of networks based on a quality function involving intensities of the two modes in order to see how networks with the above trade-off relationship can emerge through evolution. We show that the trade-off relationship can be observed in the evolved networks only when the dynamic mode is dominant in the quality function by numerical simulations. We also show that the evolved networks have features qualitatively similar to real biological networks by standard complex network analysis.Comment: 59 pages, minor corrections from v

Micro-behaviors and structural properties of knowledge networks: toward a 'one size fits one'cluster policy

The economic returns of cluster policies have been recently called into question. Based on a “one size fits all” approach consisting in boosting R&D collaborations and reinforcing network density, cluster policies are suspected to have failed in reaching their objectives. The paper proposes to go back to the micro foundations of clusters in order to disentangle the links between the long run performance of clusters and their structural properties. We use a simple agent-based model to shed light on how individual motives to build knowledge relationships can give rise to emerging structures with different properties, which imply different innovation and renewal capacities. The simulation results are discussed in a micro-macro perspective, and motivate suggestions to reorient cluster policy guidelines towards more targeted public-funded incentives for R&D collaboration

The trade-off between chain performance and fragility considering coordination strategies of agri-food chains : a South African egg chain’s case study

The mainstream strategy in the coordination of agri-food chains has traditionally focused more on the enhancement of chain performance by adopting lean and highly integrated strategies. These strategies are premised on the principle that governance structures are the result of tactics that economize on transaction costs in exchanges in chains. Due to existing interdependencies between chain players such strategies expose these chains to detrimentally disruptive uncertainty. This paper adopted a heuristic stress-testing approach to measure the fragility of South African egg value chain and performed a comparative fragility analysis of two coordination approaches in the egg chain. Additionally, the analysis of results indicated that the egg chain strategy with high levels of interdependencies between its chain players as significantly fragile. Precisely, the difference between the chain strategies was associated with a variety of differences at the factor and chain player levels that led up to a higher overall chain fragility of the chain with higher levels of interdependency. Inevitably, the paper propositions that there is a trade-off between chain performance and fragility. The results of the study affirmed that there is a trade-off between chain performance and fragility which needs to be balanced.The African Economic Research Consortium (AERC), through its Collaborative Masters in Agricultural and Applied Economics (CMAAE) programme.http://www.wageningenacademic.com/loi/ifamram2022Agricultural Economics, Extension and Rural Developmen

Networks that optimize a trade-off between efficiency and dynamical resilience

In this Letter we study networks that have been optimized to realize a trade-off between communication efficiency and dynamical resilience. While the first is related to the average shortest pathlength, we argue that the second can be measured by the largest eigenvalue of the adjacency matrix of the network. Best efficiency is realized in star-like configurations, while enhanced resilience is related to the avoidance of short loops and degree homogeneity. Thus crucially, very efficient networks are not resilient while very resilient networks lack in efficiency. Networks that realize a trade-off between both limiting cases exhibit core-periphery structures, where the average degree of core nodes decreases but core size increases as the weight is gradually shifted from a strong requirement for efficiency and limited resilience towards a smaller requirement for efficiency and a strong demand for resilience. We argue that both, efficiency and resilience are important requirements for network design and highlight how networks can be constructed that allow for both

Introducció a l’anàlisi i generació de topologies

Les xarxes de comunicació, en especial Internet, han assolit un nivell d’importància inimaginable fa uns anys. Una forma per millorar la xarxa és estudiar-la a nivell topològic, per tal de poder comprendre-la millor i poder implementar nous algoritmes i noves tecnologies que permetin augmentar el rendiment. L’estudi d’aquestes xarxes es fa mitjançant grafs. Hi han diferents tipus de topologies complexes IPs. La majoria d’elles són específiques d’un tipus de xarxes concretes, però en aquest TFC es centra en els 3 casos més importants. L’estudi de les xarxes es fa mitjançant grafs. L’objectiu principal d’aquest TFC ha estat centrat en l’anàlisi de topologies complexes per a xarxes a nivell IP, mitjançant grafs. Existeixen programes per ajudar-nos a analitzar grafs. Durant aquest projecte s’ha fet servir el programa Pajek per l’anàlisi dels grafs. S’ha combinat amb R, que és un programa per a càlculs matemàtics, amb una llibreria especial per a l’estudi dels grafs (Igraph). S’inclou un manual dels comandes que s’han anat fent servir amb Pajek, i un seguit d’exemples per a facilitar la comprensió, ja que aquest treball està previst que sigui d’ajut a altres estudiants que vulguin continuar l’anàlisi de topologies complexes. Com no ha estat possible analitzar el graf complet d’Internet, es va decidir fer una aproximació. S’ha analitzat una petita porció de la xarxa obtinguda per altres projectes de recerca, i s’ha anat incrementant la seva dimensió fins a arribar a una xarxa formada per aproximadament 300.000 nodes. Es pot veure la tendència i podem fer-nos a la idea de quines característiques té Internet. Més endavant es va disposar d’informació més precisa extreta de la xarxa (informació proporcionada per CAIDA), la qual permet estudiar una aproximació d’Internet molt més realista, en un graf format per 3.300.000 nodes. També s’ha pogut estudiar com estan estructurats els routers dins del Sistemes Autònoms

Energy-aware routing techniques for software-defined networks

Achieving energy efficiency has recently become a key topic of networking research due to the ever-increasing power consumption and CO2 emissions generated by large data networks. This problem is becoming even more concerning and challenging given the drastic traffic increase expected over the next few years. However, the use of efficient energy-aware strategies could overturn this situation reducing the electricity consumption of Internet data transmission networks, as well as contributing to mitigate the environmental impact of other sectors. The existence of redundant network elements with high capacities is a common design practice in current network infrastructures in order to face suddenly failures or peak traffic flows. However, these additional resources remain either unused or barely used most of the time leading to an undesired energy waste. Therefore, putting into sleep mode (i.e. a low-power state) unused elements is an effective and widely-accepted strategy to decrease the consumption of data networks. In this context, SDN can be seen as an attractive solution to achieve the long-awaited energy efficiency in current communications systems, since they allow a flexible programmability suitable for this problem. This doctoral thesis tackles the problem of optimizing the power consumption in SDN through the design of energy-aware routing techniques that minimize the number of network elements required to satisfy an incoming traffic load. Different from existing related works, we focus on optimizing energy consumption in SDN with in-band control traffic in order to close this important gap in the literature and provide solutions compatible with operational backbone networks. Complementing the general aim of improving the energy efficiency in SDN, this research is also intended to cover important related features such as network performance, QoS requirements and real-time operation. Accordingly, this study gives a general perspective about the use of energy efficient routing techniques, which cover integrated routing considerations for the data and control plane traffic in SDN. By using realistic input data, significant values of switched-off links and nodes are reached, which demonstrates the great opportunity for saving energy given by our proposals. The obtained results have also validated the intrinsic trade-off between environmental and performance concerns, considering several performance indicators. These findings confirm that energy-aware routing schemes should be designed considering specific traffic requirements and performance metric bounds. Moreover, it is shown that jointly considering QoS requirements and energy awareness is an effective approach to improve, not only the power consumption, but the performance on critical parameters such as control traffic delay and blocking rate. Similarly, the proposed dynamic traffic allocation with congestion-aware rerouting is able to handle demanding traffic arrival without degrading the performance of higher priority traffic. In general, our proposals are fine-grained, easy to implement and quite balanced and effective in their results looking for a suitable and readily deployment in real-world SDN scenarios. Therefore, the conducted research and contributions reported through this document not only add to what is known about the potential of energy-aware routing techniques, but also stand as a valuable solution on the road to a sustainable networking.L'assoliment de l'eficiència energètica s'ha convertit recentment en un tema clau de recerca de xarxes a causa dels creixents nivells de consum d'energia i emissions de CO2 generats per les xarxes de dades. Aquest problema es torna cada vegada més preocupant i desafiant, donat el dràstic augment del trànsit esperat en els propers anys. No obstant això, l'ús d'estratègies energètiques eficients podria invertir aquesta situació, reduint el consum d'electricitat de les xarxes de dades d'Internet i contribuint a mitigar l'impacte ambiental d'altres sectors. L'existència d'elements de xarxa redundants i amb grans capacitats és una pràctica de disseny habitual en les infraestructures de xarxes actuals per afrontar fallades sobtades o fluxos de trànsit més elevats. Tanmateix, aquests recursos addicionals romanen poc o gens utilitzats la major part del temps, generant un desaprofitament d'energia no desitjat. Per tant, posar en mode de repòs (és a dir, un estat de baixa potència) elements no utilitzats és una estratègia efectiva i àmpliament acceptada per disminuir el consum en xarxes de dades. En aquest context, les xarxes definides per programari (SDN) es poden considerar una solució atractiva per aconseguir l'esperada eficiència energètica en els sistemes de comunicacions actuals, ja que permeten una flexible programabilitat idònia per a aquest problema. Aquesta tesi doctoral aborda el problema d'optimitzar el consum d'energia en SDN a través del disseny de tècniques d'encaminament conscients de l'energia que minimitzen la quantitat d'elements de xarxa necessaris per satisfer una càrrega de trànsit entrant. Diferent dels treballs existents, aquesta tesi es centra a optimitzar el consum d'energia en SDN amb el control de tràfic dins de banda per tancar aquesta important bretxa en la literatura i proporcionar solucions compatibles amb xarxes troncals operatives. Complementant l'objectiu general de millorar l'eficiència energètica en SDN, aquesta recerca també pretén cobrir altres importants paràmetres relacionats, com ara el rendiment de la xarxa, els requisits de qualitat de servei (QoS) i el funcionament en temps real. En conseqüència, aquest estudi ofereix una perspectiva general sobre l'ús de tècniques d'encaminament eficients energèticament, que contempla consideracions integrades per al tràfic de dades i del pla de control en SDN. Prenent dades d'entrada realistes, es van aconseguir desconnectar significatives quantitats d'enllaços i nodes, la qual cosa demostra la gran oportunitat d'estalvi d'energia que ofereixen les nostres propostes. Els resultats obtinguts també validen el estret compromís entre les preocupacions ambientals i les qüestions de rendiment de la xarxa, considerant diversos indicadors de rendiment. Aquests resultats confirmen que els esquemes d'encaminament conscients de l'energia s'han de dissenyar tenint en compte els requisits de tràfic específics i els límits desitjats de les mètriques de rendiment. A més, es demostra que, considerant conjuntament els requisits de QoS i de l'energia necessària, és un enfocament eficaç per millorar, no només el consum d'energia, sinó també el rendiment en paràmetres crítics, com la latència del tràfic de control i la probabilitat de bloqueig. De manera semblant, l'assignació dinàmica de tràfic proposta, amb re-encaminament conscient de la congestió, permet gestionar grans volums de trànsit sense degradar el rendiment de les demandes de major prioritat. En general, les nostres propostes són precises, fàcils d'implementar i bastant equilibrades i efectives en els seus resultats, buscant un desplegament adequat i fàcil en escenaris pràctics de SDN. Per tant, la recerca realitzada i les contribucions contingudes en aquest document no només afegeixen el que es coneix sobre el potencial de les tècniques d'encaminament conscients de l'energia, sinó que també representen una valuosa solució en el camí cap a una xarxa sostenibl

Understanding cluster dynamics in evolutionary economic geography : essays on the structure of networks and clusters life style

L’objectif principal de cette thèse est d’étudier l’évolution des clusters. La littérature concernant les clusters s’est longuement intéressée aux raisons de leur existence ainsi qu’à la manière dont ils favorisent l’innovation, la productivité et la croissance. Nous étudions comment ces effets durent dans le temps, poursuivant l’objectif d’identifier les déterminants de la performance dynamique des clusters. Il s’agit, ainsi, d’expliquer pourquoi certains clusters déclinent tandis que d’autres continuent à fonctionner grâce à un renouveau constant. Cette thèse adopte une approche des clusters par les réseaux. Nous défendons l’idée que les structures de réseau hétérogènes des clusters démontrent des capacités différentes à s’associer ou à se dissocier des cycles industriels/technologiques au bon moment. Ainsi, nous identifions les propriétés de structure du réseau qui favorisent la performance dynamique des clusters ou la résilience des clusters. Nous appuyons nos développements théoriques sur des regards empiriques dans deux contextes bien différents. D’une part, nous étudions les structures des clusters de l’industrie de la téléphonie mobile en Europe. D’autre part, nous analysons la structure des relations entre les producteurs de fromage d’Aculco (Mexique). Le résultat principal de ce travail montre que la hiérarchie et la disassortativité des réseaux, ainsi que les interactions entre des réseaux de natures différentes (multiplexité), influencent la capacité des clusters à éviter les lock-in négatifs, conduisant à leur déclin, et favorisent le lock-out pour la survie du cluster, c’est-à-dire la prolongation de leur vie.The main objective of this thesis is to study clusters’ evolution. The literature on clusters has widely studied why clusters exist and how they favor innovation, productivity and growth. Our concern is to study how these effects hold over time. Therefore, we aim at identifying the determinants of dynamic performance of clusters to explain why some clusters decline while others keep working by continuous renewal. To do so, this thesis approaches clusters from a network perspective. We contend that clusters with heterogeneous network structures exhibit different capacities to associate and dissociate cluster’s evolution and industrial/technological cycle at the right moment. Thus, we identify the properties of network structures that favor dynamic performance of clusters or cluster resilience. We support our theoretical developments with empirical insights in two different contexts. On the one hand, we study the structure of clusters in the European mobile phone industry. On the other hand, we analyze the structure of relations between cheese producers in Aculco (Mexico). The main result of this work is that network hierarchy, network disassortativity and the interplay between different networks (multiplexity) influence the capacity of clusters to avoid negative lock-in leading to cluster failure, and favor lock-out to enhance cluster continuation, i.e. extending the life of the cluster