Up-down symmetry of the turbulent transport of toroidal angular momentum in tokamaks

Two symmetries of the local nonlinear delta-f gyrokinetic system of equations in tokamaks in the high flow regime are presented. The turbulent transport of toroidal angular momentum changes sign under an up-down reflection of the tokamak and a sign change of both the rotation and the rotation shear. Thus, the turbulent transport of toroidal angular momentum must vanish for up-down symmetric tokamaks in the absence of both rotation and rotation shear. This has important implications for the modeling of spontaneous rotation.Comment: 15 pages, 2 figure

Competition against peer-to-peer networks

In this paper, we consider the competition of providers of information products against P2P networks that offer illegal versions of the information products. Depending on the generic cost factor of downloading—incorporating factors including, among other things, the degree of legal enforcement of intellectual property rights—we find that the firm may employ pricing strategies to either deter the entry of a network or to accommodate it. In the latter case, we find that the equilibrium price moves in the opposite direction of the generic cost factor of downloading. This counter-intuitive result corresponds to a very subtle form of platform competition between the firm and the network. Furthermore, profits for the firm ambiguously decrease when the generic cost factor of downloading declines, whereas total welfare unambiguously increases. This implies that it may well be welfare enhancing to relax the legal enforcements of intellectual property rights.Strategy;

Piracy on the internet: Accommodate it or fight it? A dynamic approach

This paper uses a dynamic stochastic model to solve for the optimal pricing policy of themusic recording companies in the presence of P2P file-sharing networks eroding their CDsales. We employ a policy iteration algorithm on a discretized state space to numericallycompute the optimal price policy. The realistically calibrated model reflects the real-worldfigures we observe and provides estimates of figures we can not observe, such as changesin total welfare. The results suggest that, thanks to the existence of P2P networks, totalwelfare in 2008 in the U.S. is about $25.6 billion more per annum than in 1999 before P2Pwas introduced. Moreover, the results predict that the current trend of decreasing CDsales will continue until around the year 2020 when it will stabilize at around 231.2 millioncopies per year, comparing to the industry all-time high of 938.9 million in 1999. Thecomparative static analysis shows that full enforcement of intellectual property rights,although helpful for the industrial profit, may have adverse effect on total welfare.microeconomics ;

Changing guards: time to move beyond Body Mass Index for population monitoring of excess adiposity

With the obesity epidemic, and the effects of aging populations, human phenotypes have changed over two generations, possibly more dramatically than in other species previously. As obesity is an important and growing hazard for population health, we recommend a systematic evaluation of the optimal measure(s) for population-level excess body fat. Ideal measure(s) for monitoring body composition and obesity should be simple, as accurate and sensitive as possible, and provide good categorisation of related health risks. Combinations of anthropometric markers or predictive equations may facilitate better use of anthropometric data than single measures to estimate body composition for populations. Here we provide new evidence that increasing proportions of aging populations are at high health-risk according to waist circumference, but not body mass index (BMI), so continued use of BMI as the principal population-level measure substantially underestimates the health-burden from excess adiposity

Structural health monitoring concepts for bridge strengthening - requirement, basics and implementation

Aufgrund der ungünstigen Entwicklung der Altersstruktur bestehender Brücken und den damit verbundenen Abnutzungserscheinungen und Schäden sowie der stetigen Steigerung der Verkehrsbeanspruchung besteht ein enormer Bedarf für die tragfähigkeitsrelevante Verstärkung von Massivbrücken im Bundesfernstraßennetz. Wie groß die Wirksamkeit und die dauerhafte Funktionsfähigkeit zur Verfügung stehender Verstärkungstechniken ist, kann oftmals jedoch im Rahmen der Bauwerksprüfungen nicht hinlänglich und objektiv überprüft werden. Darüber hinaus müssen die vorhandenen finanziellen Mittel sinnvoll mit Hilfe eines effizienten Erhaltungsmanagements eingesetzt werden. Die Ziele dieser Arbeit sind zum einen, den Verstärkungsbedarf beziehungsweise die Notwendigkeit zur Verstärkung von Massivbrücken im Bundesfernstraßennetz anhand von vorhandenen Bauwerks- und Schadensdaten grundsätzlich zu untersuchen. Die Analyse erfolgt dabei nicht objektbezogen für einzelne Bauwerke, sondern mit Hilfe von Methoden der Risikobewertung für häufig im Bestand befindliche Bauwerkstypen und Konstruktionsweisen, die repräsentativ für den Brückenbestand sind. Zum anderen besteht die Motivation der Arbeit darin, messtechnisch gestützte Konzepte für die Überwachung tragfähigkeitsrelevanter Verstärkungen von Massivbrücken zu erarbeiten, die der Bewertung der Wirksamkeit und der dauerhaften Funktionsfähigkeit von Verstärkungsmaßnahmen dienen. Dazu erfolgt im Anschluss an die konzeptionelle Entwicklung eine prototypische Implementierung eines Überwachungskonzeptes an einem realen Brückenbauwerk. Die Ergebnisse der Arbeit dienen insbesondere dem Erkenntnisgewinn hinsichtlich der Planung, Umsetzung und Überwachung zukünftiger Instandsetzungs- und Verstärkungskonzepte für Massivbrücken im Rahmen eines effizienten Erhaltungsmanagements

A review of surrogate models and their application to groundwater modeling

The spatially and temporally variable parameters and inputs to complex groundwater models typically result in long runtimes which hinder comprehensive calibration, sensitivity, and uncertainty analysis. Surrogate modeling aims to provide a simpler, and hence faster, model which emulates the specified output of a more complex model in function of its inputs and parameters. In this review paper, we summarize surrogate modeling techniques in three categories: data-driven, projection, and hierarchical-based approaches. Data-driven surrogates approximate a groundwater model through an empirical model that captures the input-output mapping of the original model. Projection-based models reduce the dimensionality of the parameter space by projecting the governing equations onto a basis of orthonormal vectors. In hierarchical or multifidelity methods the surrogate is created by simplifying the representation of the physical system, such as by ignoring certain processes, or reducing the numerical resolution. In discussing the application to groundwater modeling of these methods, we note several imbalances in the existing literature: a large body of work on data-driven approaches seemingly ignores major drawbacks to the methods; only a fraction of the literature focuses on creating surrogates to reproduce outputs of fully distributed groundwater models, despite these being ubiquitous in practice; and a number of the more advanced surrogate modeling methods are yet to be fully applied in a groundwater modeling context

Competition against peer-to-peer networks

In this paper, we consider the competition of a monopolistic provider of information products against a peer-to-peer file-sharing network that offers illegal versions of the products. We focus on the role of direct externalities caused by the P2P file-sharing technology rather than the indirect consumption externalities studied previously in the literature. In our model the market structure is endogenous and we characterize three possible scenarios where the firm uses monopoly pricing, network-deterring pricing, and network-accommodating pricing, respectively. We make a full comparative-static analysis of prices, quantities, profits, consumer surplus and total surplus for each of the scenarios as well as a comparison across scenarios. We show that in the case of network-accommodating pricing, the firm sets a higher price when facing a lower generic cost factor of downloading. Furthermore, in all scenarios, profits for the firm unambiguously decrease when the generic cost factor of downloading declines; total welfare unambiguously increases, however, a result that has implications for intellectual property rights enforcement policy. (C) 2010 Elsevier B.V. All rights reserved.</p

Blind dates:Exploring uncertainty in the radiocarbon evidence on the emergence of animal husbandry in the Dutch wetlands

The emergence of animal husbandry in the Netherlands remains the subject of much speculation. Challenges in identifying domesticated animals among the faunal remains, inconsistent excavation documentation, and flawed radiocarbon analysis have resulted in questionable chronologies. This paper examines the available radiocarbon evidence from selected sites which are the mainstay of early examples of domesticated animals in the Netherlands, between 5000 and 4000 BCE.1 We approach the legacy data in two ways: by employing principles of chronometric hygiene to reassess the radiocarbon datasets of selected sites and by exploring the use of such data for future studies in chronology by means of Bayesian chronological modelling. The latter is demonstrated with a case study, whereby we employ legacy data from Hardinxveld-Giessendam De Bruin in Bayesian models to demonstrate that, despite their shortcomings, such dates remain a valuable resource for much needed future chronological analysis

High-resolution Bayesian chronology of the earliest evidence of domesticated animals in the Dutch wetlands (Hardinxveld-Giessendam archaeological sites)

The archaeological sites of Hardinxveld-Giessendam de Bruin and Polderweg, situated in the Rhine-Meuse delta, are the best-preserved Mesolithic sites in the Netherlands. Due to the early appearance of domesticated animals in their faunal assemblage, they are also integral to the research of the emergence of animal husbandry in the region. This study focuses on the precise chronology of the sites, using radiocarbon dating and Bayesian modelling of both newly acquired and legacy radiocarbon dates. To mitigate the risk of erroneous dates, we dated the bone collagen of 26 herbivorous and one aquatic mammals from clear archaeological contexts and discovered that the most recent occupational phases at both sites are several centuries younger than previously thought. This is consistent with material evidence of lifestyle changes in the final phase at Hardinxveld-Giessendam de Bruin, which is now, according to our chronology, contemporaneous with the similar patterns produced in the region