Cycling and reciprocity in weighted food webs and economic networks

Networks of mass flows describe the basic structure of ecosystems as food webs, and of economy as input–output tables. Matter leaving a node in these networks can return to it immediately as part of a reciprocal flow, or completing a longer, multi-node cycle. Previous research comparing cycling of matter in ecosystems and economy was limited by relying on unweighted or few networks. Overcoming this limitation, we study mass cycling in large datasets of weighted real-world networks: 169 mostly aquatic food webs and 155 economic networks. We quantify cycling as the portion of all flows that is due to cycles, known as the Finn Cycling Index (FCI). We find no correlation between FCI and the largest eigenvalues of unweighted adjacency matrices used as a cycling proxy in the past. Unweighted networks ignore the actual flow values that in reality can differ by even 10 orders of magnitude. FCI can be decomposed into a sum of contributions of individual nodes. This enables us to quantify how organisms recycling dead organic matter dominate mass cycling in weighted food webs. FCI of food webs has a geometric mean of 5%. We observe lower average mass cycling in the economic networks. The global production network had an FCI of 3.7% in 2011. Cycling in economic networks (input–output tables and trade relationships) and food webs strongly correlates with reciprocity. Encouraging reciprocity could enhance cycling in the economy by acting locally, without the need to perfectly know its global structure

Jan Tinbergen’s Legacy for Economic Networks: From the Gravity Model to Quantum Statistics

Jan Tinbergen, the first recipient of the Nobel Memorial Prize in Economics in 1969, obtained his PhD in physics at the University of Leiden under the supervision of Paul Ehrenfest in 1929. Among many achievements as an economist after his training as a physicist, Tinbergen proposed the so-called Gravity Model of international trade. The model predicts that the intensity of trade between two countries is described by a formula similar to Newton's law of gravitation, where mass is replaced by Gross Domestic Product. Since Tinbergen's proposal, the Gravity Model has become the standard model of non-zero trade flows in macroeconomics. However, its intrinsic limitation is the prediction of a completely connected network, which fails to explain the observed intricate topology of international trade. Recent network models overcome this limitation by describing the real network as a member of a maximum-entropy statistical ensemble. The resulting expressions are formally analogous to quantum statistics: the international trade network is found to closely follow the Fermi-Dirac statistics in its purely binary topology, and the recently proposed mixed Bose-Fermi statistics in its full (binary plus weighted) structure. This seemingly esoteric result is actually a simple effect of the heterogeneity of world countries, that imposes strong structural constraints on the network. Our discussion highlights similarities and differences between macroeconomics and statistical-physics approaches to economic networks

Energy conservation more effective with rebound policy

This article sketches the problem of indirect energy use effects, also known as rebound, of energy conservation. There is widespread support for energy conservation, especially when it is voluntary, as this seems a cheap way to realize environmental and energy-climate goals. However, this overlooks the phenomenon of rebound. The topic of energy rebound has mainly attracted attention from energy analysts, but has been surprisingly neglected in environmental economics, even though economists generally are concerned with indirect or economy-wide impacts of technical change and policies. This paper presents definitions and interpretations of energy and environmental rebound, as well as four fundamental reasons for the existence of the rebound phenomenon. It further offers the most complete list of rebound pathways or mechanisms available in the literature. In addition, it discusses empirical estimates of rebound and addresses the implications of uncertainties and difficulties in assessing rebound. Suggestions are offered for strategies and public policies to contain rebound. It is advised that rebound evaluation is an essential part of environmental policy and project assessments. As opposed to earlier studies, this paper stresses the relevance of the distinction between energy conservation resulting from autonomous demand changes and from efficiency improvements in technology/equipment. In addition, it argues that rebound is especially relevant for developing countries. © 2010 The Author(s)

Evidences for a structural change in the oil market before a financial crisis: The flat horizon effect

There are growing evidences that the commodity bubble in the 2000s had a major impact in the 2007–08 financial crisis. A salient feature of this commodity bubble was the dramatic increasing in the correlation of indexed commodities with oil price following the financialisation of the oil market. In this paper we suggest that, besides the growing demand from emerging economies and the following inflow of money from speculative traders, the introduction of the electronic platform could have had an important and underestimated effect on the oil market. Our analysis of the spot and futures oil prices at the NYMEX based on the Generalized Hurst Exponent confirms that the period 2004–2007 is pivotal in the oil market and corroborates the hypothesis that a structural change occurred in both markets. The evident decrease in multifractality suggests a flattening of the time horizon in financial oil markets and the coexistence of long-termism and short-termism. This structural change could partially explain the observed increase of correlations between commodities and oil price

Hepatic heparan sulfate is a master regulator of hepcidin expression and iron homeostasis in human hepatocytes and mice

Hepcidin is a liver-derived peptide hormone that controls systemic iron homeostasis. Its expression is regulated by the bone morphogenetic protein 6 (BMP6)/SMAD1/5/8 pathway and by the proinflammatory cytokine interleukin 6 (IL6). Proteoglycans that function as receptors of these signaling proteins in the liver are commonly decorated by heparan sulfate, but the potential role of hepatic heparan sulfate in hepcidin expression and iron homeostasis is unclear. Here, we show that modulation of hepatic heparan sulfate significantly alters hepcidin expression and iron metabolism both in vitro and in vivo. Specifically, enzymatic removal of heparan sulfate from primary human hepatocytes, CRISPR/Cas9 manipulation of heparan sulfate biosynthesis in human hepatoma cells, or pharmacological manipulation of heparan sulfate–protein interactions using sodium chlorate or surfen dramatically reduced baseline and BMP6/SMAD1/5/ 8-dependent hepcidin expression. Moreover inactivation of the heparan sulfate biosynthetic gene N-deacetylase and N-sulfotransferase 1 (Ndst1) in murine hepatocytes (Ndst1f/fAlbCre+) reduced hepatic hepcidin expression and caused a redistribution of systemic iron, leading to iron accumulation in the liver and serum of mice. Manipulation of heparan sulfate had a similar effect on IL6-dependent hepcidin expression in vitro and suppressed IL6-mediated iron redistribution induced by lipopolysaccharide in vivo. These results provide compelling evidence that hepatocyte heparan sulfate plays a key role in regulating hepcidin expression and iron homeostasis in mice and in human hepatocytes