Infrared dynamics in de Sitter space from Schwinger-Dyson equations

We study the two-point correlator of an O(N) scalar field with quartic self-coupling in de Sitter space. For light fields in units of the expansion rate, perturbation theory is plagued by large logarithmic terms for superhorizon momenta. We show that a proper treatment of the infinite series of self-energy insertions through the Schwinger-Dyson equations resums these infrared logarithms into well defined power laws. We provide an exact analytical solution of the Schwinger-Dyson equations for infrared momenta when the self-energy is computed at two-loop order. The obtained correlator exhibits a rich structure with a superposition of free-field-like power laws. We extract mass and field-strength renormalization factors from the asymptotic infrared behavior. The latter are nonperturbative in the coupling in the case of a vanishing tree-level mass.Comment: 9 pages, 3 figures, published version, some material has been added, title change

What do internal capital markets do ? Redistribution vs. incentives

In this paper we explain the apparent "diversification discount” of conglomerates without assuming inefficient-cross subsidisation through internal capital markets. Instead we assume that internal capital market efficiently redistributes scare resources across a conglomerate’s divisions between sucessive production periods. The need for redistribution arises from the fact that resources may sometimes be produced by divisions which happen to be successful in an earlier production stage but which do not have the best investment opportunities in future production stages. In contrast to the existing literature we consider explicitly the incentive problem between corporate headquater and divisional managers using a standard Moral-Hazard framework. We show that although a complete incentive contract can be written bi-laterally between headquarter and divisional managers, the redistribution of resources across divisions creates additional agency costs in a conglomerate. Moreover, assuming that no complete contract can govern the interim redistribution policy by the headquarter, we show how the agency problem with divisional managers constrains headquarters interim redistribution to be ex ante inefficient.

The Benefit and Cost of Winner Picking: Redistribution Vs Incentives

The Benefit and Cost of Winner Picking: Redistribution Vs Incentives |AB| A multi-divisional firm can engage in "winner-picking" to redistribute scarce funds efficiently across divisions. But there is a conflict between rewarding winners (investing) and producing resources internally to reward winners (incentives). Managers in winning divisions are tempted to free-ride on resources produced by managers in loosing divisions whose incentives to produce resources, anticipating their loss, are also weakened. Corporate headquarter's investment and incentive policy are therefore inextricably linked and have to be treated as jointly endogenous. The analysis links corporate strategy, compensation and the value of diversification to the characteristics of multi-divisional firms.Conglomerate, Internal capital market

Gigwa—Genotype investigator for genome-wide analyses

Background Exploring the structure of genomes and analyzing their evolution is essential to understanding the ecological adaptation of organisms. However, with the large amounts of data being produced by next-generation sequencing, computational challenges arise in terms of storage, search, sharing, analysis and visualization. This is particularly true with regards to studies of genomic variation, which are currently lacking scalable and user-friendly data exploration solutions. Description Here we present Gigwa, a web-based tool that provides an easy and intuitive way to explore large amounts of genotyping data by filtering it not only on the basis of variant features, including functional annotations, but also on genotype patterns. The data storage relies on MongoDB, which offers good scalability properties. Gigwa can handle multiple databases and may be deployed in either single- or multi-user mode. In addition, it provides a wide range of popular export formats. Conclusions The Gigwa application is suitable for managing large amounts of genomic variation data. Its user-friendly web interface makes such processing widely accessible. It can either be simply deployed on a workstation or be used to provide a shared data portal for a given community of researchers. (Résumé d'auteur

One single static measurement predicts wave localization in complex structures

A recent theoretical breakthrough has brought a new tool, called \emph{localization landscape}, to predict the localization regions of vibration modes in complex or disordered systems. Here, we report on the first experiment which measures the localization landscape and demonstrates its predictive power. Holographic measurement of the static deformation under uniform load of a thin plate with complex geometry provides direct access to the landscape function. When put in vibration, this system shows modes precisely confined within the sub-regions delineated by the landscape function. Also the maxima of this function match the measured eigenfrequencies, while the minima of the valley network gives the frequencies at which modes become extended. This approach fully characterizes the low frequency spectrum of a complex structure from a single static measurement. It paves the way to the control and engineering of eigenmodes in any vibratory system, especially where a structural or microscopic description is not accessible.Comment: 5 pages, 4 figure

Conception itérative et semi-supervisée d'assistants conversationnels par regroupement interactif des questions

National audienceThe design of a dataset needed to train a chatbot is most often the result of manual and tedious step. To guarantee the efficiency and objectivity of the annotation, we propose an active learning method based on constraints annotation. It’s an iterative approach, relying on a clustering algorithm to segment data and using annotator knowledge to lead clustering from unlabeled question to relevant intents structure. In this paper, we study the optimal modeling parameters to get an exploitable dataset with a minimum of annotations, and show that this approach allows to make a coherent structure for the training of a chatbot.La création d’un jeu de données pour l’entrainement d’un chatbot repose sur un a priori de connaissance du domaine. En conséquence, cette étape est le plus souvent manuelle, fastidieuse et soumise aux biais. Pour garantir l’efficacité et l’objectivité de l’annotation, nous proposons une méthodologie d’apprentissage actif par annotation de contraintes. Il s’agit d’une approche itérative, reposant sur un algorithme de clustering pour segmenter les données et tirant parti de la connaissance de l’annotateur pour guider le regroupement des questions en une structure d’intentions. Dans cet article, nous étudions les paramètres optimaux de modélisation pour réaliser une segmentation exploitable en un minimum d’annotations, et montrons que cette approche permet d’aboutir à une structure cohérente pour l’entrainement d’un assistant conversationnel

Towards drop your thesis 2018: 4.7 seconds of microgravity conditions to enable future CubeSat landings on asteroids

An increasing number of interplanetary missions are aiming at visiting asteroids and other small bodies, since these may provide clues to understand the formation and evolution of our Solar System. CubeSats allow a low-cost solution to land on these objects, as opposed to risking a much more expensive mothership. The weak gravitational field on these small bodies may also enable the possibility of simply dropping a CubeSat from afar (i.e. ballistic landing). However, ballistic landing of an unpowered spacecraft may be feasible solely within certain asteroid locations, and only if sufficient energy can be dissipated at touchdown. If such conditions are not met, the spacecraft will rebound off the surface. It is likely that the necessary energy dissipation may already occur naturally due to energy loss expected through the deformation of the regolith during touchdown. Indeed, previous low-velocity impact experiments in microgravity seem to indicate that this is exactly the case. However, data from past asteroid touchdowns, Hayabusa and Philae, indicate the contrary. This paper describes the development of an experiment which aims to bridge the aforementioned disagreement between mission data and microgravity experiment; to understand the behaviour of CubeSat landing on asteroids. The experiment will also test a novel damping system made by origami paper that should increase the dissipated energy at touchdown. The experiment will take place at the ZARM Drop Tower in Bremen in November 2018. With the constraint of 5 drops, the experiment will measure the coefficient of restitution during an available time window of 4.74 seconds of microgravity conditions. A 1UCubeSat mock-up will be used to represent a future asteroid lander. In order to mimic the landing of actual missions, the mock-up will have a mass of about 4 kg and it will be given a velocity of 15 cm/s with minimal rotation. This will be achieved by an automated spring-based release mechanism. An asteroid simulant, ESA03-A KM Bentonite Granules will be used to replicate an asteroid mechanical properties at the surface. This paper reviews the final design and the engineering challenges of the experiment