Gauge theory of Finance?

Some problems with the recent stimulating proposal of a ``Gauge Theory of Finance'' by Ilinski and collaborators are outlined. First, the derivation of the log-normal distribution is shown equivalent both in information and mathematical content to the simpler and well-known derivation, dating back from Bachelier and Samuelson. Similarly, the re-derivation of Black-Scholes equation is shown equivalent to the standard one because the limit of no uncertainty is equivalent to the standard risk-free replication argument. Both re-derivations of the log-normality and Black-Scholes result do not provide a test of the theory because it is degenerate in the limits where these results apply. Third, the choice of the exponential form a la Boltzmann, of the weight of a given market configuration, is a key postulate that requires justification. In addition, the ``Gauge Theory of Finance'' seems to lead to ``virtual'' arbitrage opportunities for pure Markov random walk market when there should be none. These remarks are offered in the hope to improve the formulation of the ``Gauge Theory of Finance'' into a coherent and useful framework.Comment: 4 page

KnowSe: Fostering user interaction context awareness

The CSCW area has recognized the concept of awareness as a critical issue to focus on (Schmidt et al., 2002) since “users who work together require adequate information about their environment” (Gross and Prinz, 2003). The environment of an individual encompasses her connections with other people, as well as with digital resources and actions (tasks or processes). If connections are not clear or hidden to the individual or to the group, the cost is a lack of awareness in the organization (McArthur and Bruza, 2003), which not only leads to inefficient cooperation but can even prevent it from being started. Unveiling the relations between persons, topics, tasks and processes to computer workers facilitates cooperative work by increasing the awareness of the personal social networks and the role of an individual in the organization, a project, or a group. These connections can be created and modeled manually but a better approach is to develop semi-automatic or even automatic tools to create and share them (McArthur and Bruza, 2003). Based on emails, McArthur and Bruza (2003) have computed such kind of connections, and suggest using more global corpora as well as taking into account dynamic ones

Detecting real user tasks by training on laboratory contextual attention metadata

Detecting the current task of a user is essential for providing her with contextualized and personalized support, and using Contextual Attention Metadata (CAM) can help doing so. Some recent approaches propose to perform automatic user task detection by means of task classifiers using such metadata. In this paper, we show that good results can be achieved by training such classifiers offline on CAM gathered in laboratory settings. We also isolate a combination of metadata features that present a significantly better discriminative power than classical ones

Peace and violence in contemporary Africa: A possibility of intercultural dialogue?*.

No Abstact

Exploiting the user interaction context for automatic task detection

Detecting the task a user is performing on her computer desktop is important for providing her with contextualized and personalized support. Some recent approaches propose to perform automatic user task detection by means of classifiers using captured user context data. In this paper we improve on that by using an ontology-based user interaction context model that can be automatically populated by (i) capturing simple user interaction events on the computer desktop and (ii) applying rule-based and information extraction mechanisms. We present evaluation results from a large user study we have carried out in a knowledge-intensive business environment, showing that our ontology-based approach provides new contextual features yielding good task detection performance. We also argue that good results can be achieved by training task classifiers `online' on user context data gathered in laboratory settings. Finally, we isolate a combination of contextual features that present a significantly better discriminative power than classical ones

Generalised Regret Optimal Controller Synthesis for Constrained Systems

This paper presents a synthesis method for the generalised dynamic regret problem, comparing the performance of a strictly causal controller to the optimal non-causal controller under a weighted disturbance. This framework encompasses both the dynamic regret problem, considering the difference of the incurred costs, as well as the competitive ratio, which considers their ratio, and which have both been proposed as inherently adaptive alternatives to classical control methods. Furthermore, we extend the synthesis to the case of pointwise-in-time bounds on the disturbance and show that the optimal solution is no worse than the bounded energy optimal solution and is lower bounded by a constant factor, which is only dependent on the disturbance weight. The proposed optimisation-based synthesis allows considering systems subject to state and input constraints. Finally, we provide a numerical example which compares the synthesised controller performance to $\mathcal{H}_2$- and $\mathcal{H}_\infty$-controllers.Comment: Accepted at IFAC WC 202

Analyse en retour d'expérience de deux effondrements miniers dans des mines de coalbrook (Afrique du Sud) et de Gardanne (France)

National audienceThe paper proposes the back analysis of two major accidents that have occurred within underground coal mines. The first one concerns the Coalbrook disaster, in South-Africa, that killed more than 400 miners. The second one deals with the collapse of a whole sector of a mine located in the Provence coal basin (SE of France). This one did not induce any victim but generated major damage for the exploitation. After a description of the contexts of the two mines as well as the manifestation of the collapses, the paper presents the major improvements in the field of rock mechanics, which resulted from the analysis of both events. In the case of Coalbrook, the researches were mainly devoted to a better characterisation of the in situ pillar strength. In the case of the Provence coal field, the development performed made it possible to analyse, with the help of numerical modelling, the mechanism 'crushing pillars - brittle roof' identify at the origin of two brutal collapses. Some perspectives and identification future developments are finally proposed.Le présent article propose l'analyse en retour d'expérience de deux accidents miniers survenus au sein de mines de charbon. Le premier est la catastrophe minière de Coalbrook en Afrique du Sud qui a coûté la vie à plus de 400 mineurs. Le second correspond à l'effondrement de tout un secteur d'une mine située dans le bassin houiller de Provence (SE de la France) qui n'a pas engendré de victimes mais a induit de gros dégâts pour l'exploitation. Après une description détaillée des contextes de ces deux mines et de la manifestation des deux effondrements, l'article présente les principales avancées dans le domaine de la mécanique des roches qui ont résulté de l'analyse de ces évènements. Si les travaux consécutifs à Coalbrook ont été principalement consacrés à une meilleure caractérisation de la résistance des piliers in situ, le travail entrepris sur le bassin houiller de Provence a permis d'analyser, par le biais de la modélisation numérique, le mécanisme " piliers déformables -toit fragile " à l'origine des deux effondrements. Une mise ne perspective des résultats et l'identification de pistes de développement complètent le document