Parabolic Harnack Inequality and Local Limit Theorem for Percolation Clusters

We consider the random walk on supercritical percolation clusters in the d-dimensional Euclidean lattice. Previous papers have obtained Gaussian heat kernel bounds, and a.s. invariance principles for this process. We show how this information leads to a parabolic Harnack inequality, a local limit theorem and estimates on the Green's function.Comment: 29 page

The benefits from publicly funded research

Research, Technological change, Government Policy

Belief Approach for Social Networks

Nowadays, social networks became essential in information exchange between individuals. Indeed, as users of these networks, we can send messages to other people according to the links connecting us. Moreover, given the large volume of exchanged messages, detecting the true nature of the received message becomes a challenge. For this purpose, it is interesting to consider this new tendency with reasoning under uncertainty by using the theory of belief functions. In this paper, we tried to model a social network as being a network of fusion of information and determine the true nature of the received message in a well-defined node by proposing a new model: the belief social network

Bailouts in federations : is a hard budget constraint always best?

This article analyses hard and soft budget constraints in a federation, where there is a moral hazard problem between the central and the regional governments. Regional governments can avoid a bailout from the center by exerting costly effort. In this setting, a hard budget constraint is not always optimal because it can provide excessive incentives for high effort, and thus discourage investment that is socially efficient. Thus, a hard budget constraint can imply the opposite kind of inefficiency that emerges under a soft budget constraint, where the common pool problem can give rise to inefficiently low effort and overinvestment

Definable equivalence relations and zeta functions of groups

We prove that the theory of the $p$-adics ${\mathbb Q}_p$ admits elimination of imaginaries provided we add a sort for ${\rm GL}_n({\mathbb Q}_p)/{\rm GL}_n({\mathbb Z}_p)$ for each $n$. We also prove that the elimination of imaginaries is uniform in $p$. Using $p$-adic and motivic integration, we deduce the uniform rationality of certain formal zeta functions arising from definable equivalence relations. This also yields analogous results for definable equivalence relations over local fields of positive characteristic. The appendix contains an alternative proof, using cell decomposition, of the rationality (for fixed $p$) of these formal zeta functions that extends to the subanalytic context. As an application, we prove rationality and uniformity results for zeta functions obtained by counting twist isomorphism classes of irreducible representations of finitely generated nilpotent groups; these are analogous to similar results of Grunewald, Segal and Smith and of du Sautoy and Grunewald for subgroup zeta functions of finitely generated nilpotent groups.Comment: 89 pages. Various corrections and changes. To appear in J. Eur. Math. So

How uncertain are the welfare costs of inflation?

This paper quantifies some of the general equilibrium costs of inflation for the UK using a shopping-time model. It tests whether money balances tend to a finite number as nominal interest rates tend to zero, and explores how uncertainties about the shape of the money demand curve translate into uncertainties about these welfare costs of inflation. A key uncertainty is the existence of a satiation point for money balances. We show that without observations at nominal interest rates close to zero, the power of satiation tests can be low.

Science and Technology Studies: Exploring the Knowledge Base

Science and Technology Studies (STS) is one of a number of new research fields to emerge over the last four or five decades. This paper attempts to identify its core academic contributions using the references that are most cited by the authors of chapters in a number of authoritative ‘handbooks’. The study then analyses the impact of these contributions by exploring the research fields, journals, and geographical location of the researchers that have cited these core contributions in their own work. Together, these two analyses reveal the various phases in the development of STS and the various aspects of convergence and divergence of the field as the quantitative studies of science and technology gradually separated from the main body of STS. The paper ends with some conclusions about the evolution of STS such as the role of ‘institution builders’ in developing new research fields and the structures required to hold them together.science studies, STS, knowledge base, handbooks, core contributions

Editors’ JIF-boosting stratagems – which are appropriate and which not?

This extended editorial explores the growing range of stratagems devised by journal editors to boost their Journal Impact Factor (JIF) and the consequences for the credibility of this indicator as well as for the academic community more broadly. Over recent years, JIF has become the most prominent indicator of a journal’s standing, bringing intense pressure on journal editors to do what they can to increase it. After explaining the curious way in which JIF is calculated and the technical limitations that beset it, we examine the approaches employed by journal editors to maximise it. Some approaches would seem completely acceptable, others (such as coercive citations and cross-citing journal cartels) are in clear breach of the conventions on academic behaviour, but a number fall somewhere in between. Over time, editors have devised ingenious ways of enhancing their JIF without apparently breaching any rules. In particular, the editorial describes the ‘online queue’ stratagem and asks whether this constitutes appropriate behaviour or not. The editorial draws three conclusions. First, in the light of ever more devious ruses of editors, the JIF indicator has now lost most of its credibility. Secondly, where the rules are unclear or absent, the only way of determining whether particular editorial behaviour is appropriate or not is to expose it to public scrutiny. Thirdly, editors who engage in dubious behaviour thereby risk forfeiting their authority to police misconduct among authors

Are Hard Budget Constraints for Sub-National Governments Always Efficient?

In fiscally decentralized countries, sub-national governments (SNGs) may face soft budget constraints and consequently invest and borrow too much. The policy literature claims that, with competitive capital markets and central governments imposing hard budget constraints (HBCs), inefficient investment by SNGs should not arise. We present a model where this is not the case : HBCs can be too "hard" and discourage investment that is socially efficient. The model combines a dynamic commitment problem as in Kornai, Maskin and Roland (2004) for central government with a moral hazard problem between central and SNG. The HBC over-incentivises the SNG to provide effort by penalizing it too much for project failure, thus leading ultimately to the possibility that socially efficient projects may not be undertaken.Fiscal federalism ; Bailouts ; Hard budget constraints

Taxonomic status of the Liberian Greenbul Phyllastrephus leucolepis and the conservation importance of the Cavalla Forest, Liberia

We thank Jochen Martens for his long-lasting patience in dealing with the specimen of leucolepis, and Brian Hillcoat for comments and advice. It is hardly possible to thank by name all those who have supported WG over the past 30 years and more since 1981 in the fields of forest ecology and ornithology in eastern Liberia. In particular, we express gratitude to Alex Peal and Theo Freeman, both Heads of Wildlife and National Parks, for their many years of cooperation, and the Silviculture Officers Wynn Bryant, Momo Kromah and Steve Miapeh. The knowledge of the tree experts Joe Keper and Daniel Dorbor helped us to gain insights into the ecological complexities of the relationship between man, birds and trees. William Toe worked for three years as bird trapper and assistant in bird banding. WG’s attachment to the University of Liberia and to the students who so often accompanied him was made possible by Ben Karmorh from the Environmental Protection Agency (EPA) and University of Liberia. NABU, the German Conservation Society, has supported the Liberian projects for almost 30 years now. We also thank Nigel Collar, Françoise Dowsett-Lemaire and Hannah Rowland for comments and advice. We thank the African Bird Club and the Royal Society for the Protection of Birds for helping to fund the 2013 expedition to the Cavalla Forest, in particular Alice Ward-Francis, Robert Sheldon, Alan Williams and Keith Betton. We also are extremely grateful to Michael Garbo and staff of the Society for the Conservation of Nature in Liberia for all manner of help with the expedition, to Harrison Karnwea and colleagues at the Forest Development Authority of Liberia for permissions and other support, as well as to Emmanuel Loqueh, Trokon Grimes, Flomo Molubah and Amos ‘Dweh’ Dorbor for being such excellent companions in the field. YL performed the genetic work as part of her M.Sc. (Genetics) at the University of Aberdeen, whose support is acknowledged.Peer reviewedPublisher PD