Valued fields, Metastable groups

We introduce a class of theories called metastable, including the theory of algebraically closed valued fields (ACVF) as a motivating example. The key local notion is that of definable types dominated by their stable part. A theory is metastable (over a sort $\Gamma$) if every type over a sufficiently rich base structure can be viewed as part of a $\Gamma$-parametrized family of stably dominated types. We initiate a study of definable groups in metastable theories of finite rank. Groups with a stably dominated generic type are shown to have a canonical stable quotient. Abelian groups are shown to be decomposable into a part coming from $\Gamma$, and a definable direct limit system of groups with stably dominated generic. In the case of ACVF, among definable subgroups of affine algebraic groups, we characterize the groups with stably dominated generics in terms of group schemes over the valuation ring. Finally, we classify all fields definable in ACVF.Comment: 48 pages. Minor corrections and improvements following a referee repor

Definable and invariant types in enrichments of NIP theories

Let T be an NIP L-theory and T' be an enrichment. We give a sufficient condition on T' for the underlying L-type of any definable (respectively invariant) type over a model of T' to be definable (respectively invariant) as an L-type. Besides, we generalise work of Simon and Starchenko on the density of definable types among non forking types to this relative setting. These results are then applied to Scanlon's model completion of valued differential fields.Comment: 9 pages. An error was pointed out in section 2 of the previous version so that section was removed. So was Proposition 3.8 that depended on i

Imaginaries in separably closed valued fields

We show that separably closed valued fields of finite imperfection degree (either with lambda-functions or commuting Hasse derivations) eliminate imaginaries in the geometric language. We then use this classification of interpretable sets to study stably dominated types in those structures. We show that separably closed valued fields of finite imperfection degree are metastable and that the space of stably dominated types is strict pro-definable

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

Addressing information flow in lean production management and control in construction

Traditionally, production control on construction sites has been a challenging area, where the ad-hoc production control methods foster uncertainty - one of the biggest enemies of efficiency and smooth production flow. Lean construction methods such as the Last Planner System have partially tackled this problem by addressing the flow aspect through means such as constraints analysis and commitment planning. However, such systems have relatively long planning cycles to respond to the dynamic production requirements of construction, where almost daily if not hourly control is needed. New solutions have been designed by researchers to improve this aspect such as VisiLean, but again these types of software systems require the proximity and availability of computer devices to workers. Given this observation, there is a need for a communication system between the field and site office that is highly interoperable and provides real-time task status information. A High-level communication framework (using VisiLean) is presented in this paper, which aims to overcome the problems of system integration and improve the flow of information within the production system. The framework provides, among other things, generic and standardized interfaces to simplify the “push” and “pull” of the right (production) information, whenever needed, wherever needed, by whoever needs it. Overall, it is anticipated that the reliability of the production control will be improve

The Impact of Banking Structural Reform on Household Retail Finance. ECRI Commentary No. 13, 7 October 2014

There are two main objectives behind the EC proposal on banking structural reform: the financial stability objective and the economic efficiency objective. If it is implemented, the reform should reinforce the stability and economic efficiency of household retail activities through lower contagion, better resolvability in the event of failure, more harmonised supervisory practices across the EU and more resilient household demand for retail loans. However, it could also trigger counterproductive effects that could partly undermine the expected benefits. These potential negative effects are not appropriately assessed in the impact study of the proposal published in January 2014 and will require further consideration in the coming months. In particular, the stability of household retail finance could be strengthened by placing more emphasis on bankruptcy risks of retail banks; the transfer of existing systemic activities towards less regulated and supervised markets and reputational risk. A better analysis of the borrowing costs for households (impacted by the potential decreasing diversification of the funding base of banks and scarcer liquidity) and implementation costs could help regulators to achieve the objective of efficient household activities

User Generated Diversity. Some reflections on how to improve the quality of amateur productions

The potential of user created content to make a meaningful contribution to media diversity is subject to debates. Central to these debates is the argument of the quality of amateur productions. This article will take a close look at this argument, and make some suggestions on how to improve the quality and utility of amateur productions with regard to the democratic functions of media.user created content, diversity, quality, strategies