Kosterlitz-Thouless signatures in the low-temperature phase of layered three-dimensional systems

We study the quasi-two-dimensional quantum O(2) model, a quantum generalization of the Lawrence-Doniach model, within the nonperturbative renormalization-group approach and propose a generic phase diagram for layered three-dimensional systems with an O(2)-symmetric order parameter. Below the transition temperature we identify a wide region of the phase diagram where the renormalization-group flow is quasi-two-dimensional for length scales smaller than a Josephson length $l_J$, leading to signatures of Kosterlitz-Thouless physics in the temperature dependence of physical observables. In particular the order parameter varies as a power law of the interplane coupling with an exponent which depends on the anomalous dimension (itself related to the stiffness) of the strictly two-dimensional low-temperature Kosterlitz-Thouless phase.Comment: v2) 11 pages, 9 figure

What drives failure to maximize payoffs in the lab ? A test of the inequality aversion hypothesis

In experiments based on the Beard and Beil (1994) game, second movers very often fail to select the decision that maximizes both players payoff. This note reports on a new experimental treatment, in which we neutralize the potential effect of inequality aversion on the likelihood of this behavior. We show this behavior is robust to this change, even after allowing for repetition-based learning.Coordination failure, laboratory experiments, aversion to inequality.

A solution for Europe's banking problem

Nicolas Véron and Adam Posen believe Europe should build new long term European joint-action to face the likely high rising number of insolvent banks on the continent. The authors propose on the one hand, a centralised triage and restructuring process of bad European banks lead by a new temporary European Institution, a European Bank Support Authority (EBSA), and on the other hand, long-term EU Institutions dedicated to the completion of an integrated market.

Learning, words and actions : experimental evidence on coordination-improving information

This paper reports experimental results from a one-shot game with two Nash equilibria: the first one is efficient, the second one relies on weakly dominated strategies. The experimental treatments consider three information-enhancing mechanisms in the game: simple repetition, cheap-talk messages and observation of past actions from the current interaction partner. Our experimental results show the use of dominated strategies is quite widespread. Any kind of information (through learning, words or actions) increases efficiency. As regards coordination, we find that good history performs better than good messages; but bad history performs worse than bad messages.Coordination game, communication, cheap-talk, observation.

Poster Abstract: Low-Power Wireless IPv6 Routing with ContikiRPL

RPL is the IETF candidate standard for IPv6 routing in low-power wireless sensor networks. We present the first experimental results of RPL which we have obtained with our ContikiRPL implementation. Our results show that Tmote Sky motes running IPv6 with RPL routing have a battery lifetime of years, while delivering 0.6 packets per second to a sink node

A Solution for Europe's Banking Problem

The European Union's aggressive response to the global financial crisis has prevented financial meltdown, but the continent's banking industry remains very fragile. Experts estimate coming losses in excess of $500 billion, with very little written down so far. These losses plus the problems in Eastern Europe portend widespread cross-border bank insolvencies. Traditional banking (in corporate finance and household savings) remains predominant in the European economies, so healing the banking system is crucial for sustained recovery in Europe. Lingering banking fragility would result in constant disruption or misallocation of bank credit and hinder returns to savers, thus depressing investment and consumption. Ongoing fragility will also harm European trend productivity growth by skipping some investment and R&D cycles, misallocating capital to lower-return projects, and wasting human capital by consigning some workers to long-term unemployment. It will take time and political will to create an EU banking supervisory architecture, but Europe cannot afford to wait. Posen and Véron recommend that Europe engage in system-wide "triage" of major banks on the continent by capital position, leading to public restructuring of the weakest ones. They propose that relevant countries jointly create a temporary supranational agency or Treuhand to implement the triage process, catalyze recapitalizations, and manage any distressed assets that would fall into public ownership. Such a trustee would avoid both harmful races to the bottom within Europe by national supervisors and fiscal transfers between European states for bailouts.

Pragmatic Low-Power Interoperability: ContikiMAC vs TinyOS LPL

Standardization has driven interoperability at multiple layers of the stack, such as the routing and application layers, standardization of radio duty cycling mechanisms have not yet reached the same maturity. In this work, we pitch the two de facto standard flavors of sender-initiated radio duty cycling mechanisms against each other: ContikiMAC and TinyOS LPL. Our aim is to explore pragmatic interoperability mechanisms at the radio duty cycling layer. This will lead to better understanding of interoperability problems moving forward, as radio duty cycling mechanisms get standardized. Our results show that the two flavors can be configured to operate together but that parameter configuration may severely hurt performance

Powertrace: Network-level Power Profiling for Low-power Wireless Networks

Low-power wireless networks are quickly becoming a critical part of our everyday infrastructure. Power consumption is a critical concern, but power measurement and estimation is a challenge. We present Powertrace, which to the best of our knowledge is the first system for network-level power profiling of low-power wireless systems. Powertrace uses power state tracking to estimate system power consumption and a structure called energy capsules to attribute energy consumption to activities such as packet transmissions and receptions. With Powertrace, the power consumption of a system can be broken down into individual activities which allows us to answer questions such as “How much energy is spent forwarding packets for node X?”, “How much energy is spent on control traffic and how much on critical data?”, and “How much energy does application X account for?”. Experiments show that Powertrace is accurate to 94% of the energy consumption of a device. To demonstrate the usefulness of Powertrace, we use it to experimentally analyze the power behavior of the proposed IETF standard IPv6 RPL routing protocol and a sensor network data collection protocol. Through using Powertrace, we find the highest power consumers and are able to reduce the power consumption of data collection with 24%. It is our hope that Powertrace will help the community to make empirical energy evaluation a widely used tool in the low-power wireless research community toolbox

Brochure

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Performance assessment of tariff-based air source heat pump load shifting in a UK detached dwelling featuring phase change-enhanced buffering

Using a detailed building simulation model, the amount of thermal buffering, with and without phase change material (PCM), needed to time-shift an air source heat pump's operation to off-peak periods, as defined by the UK 'Economy 10' tariff, was investigated for a typical UK detached dwelling. The performance of the buffered system was compared to the case with no load shifting and with no thermal buffering. Additionally, the load shifting of a population of buffered heat pumps to off-peak periods was simulated and the resulting change in the peak demand on the electricity network was assessed. The results from this study indicate that 1000 L of hot water buffering or 500 L of PCM-enhanced hot water buffering was required to move the operation of the heat pump fully to off-peak periods, without adversely affecting the provision of space heating and hot water for the end user. The work also highlights that buffering and load shifting increased the heat pump's electrical demand by over 60% leading to increased cost to the end user and increased CO2 emissions (depending on the electricity tariff applied and time varying CO2 intensity of the electricity generation mix, respectively). The study also highlights that the load-shifting of populations of buffered heat pumps wholly to off-peak periods using crude instruments such as tariffs increased the peak loading on the electrical network by over 50% rather than reducing it and that careful consideration is needed as to how the load shifting of a group of heat pumps is orchestrated