268 research outputs found
Conditionally Heteroskedastic Factor Models: Identification and Instrumental Variables Estimation
This paper provides a semiparametric framework for modelling multivariate conditional heteroskedasticity. First, we show that stochastic volatility factor models with possibly cross-correlated disturbances cannot be identified from returns conditional variance structure only, except when strong restrictions on the support of the probability distribution of latent factors volatility are maintained. Second, we provide an alternative way to maintain identifying restrictions through either higher order moments or through a specification of risk premiums based on constant prices of factor risks. In both cases, identification is obtained with conditional moment restrictions which pave the way for instrumental variables estimation and inference. A preliminary step of determination of the number of factors and identification of mimicking portfolios is proposed through a sequence of GMM overidentification tests which encompass Engle and Kozicki (1993) tests for common features. Cet article propose un cadre semi-paramĂ©trique adaptĂ© Ă la modĂ©lisation de l'hĂ©tĂ©roscĂ©dasticitĂ© conditionnelle multivariĂ©e. Nous montrons d'abord qu'un modĂšle factoriel Ă volatilitĂ© stochastique ne peut pas ĂȘtre identifiĂ© seulement Ă partir de la structure de variance conditionnelle des rendements, sauf si l'on impose des restrictions importantes au support de la loi de probabilitĂ© des facteurs latents. Nous proposons ensuite des restrictions alternatives permettant d'identifier le modĂšle de volatilitĂ© multivariĂ©e. Ces restrictions portent soit sur les moments d'ordre supĂ©rieur, soit sur une spĂ©cification de la prime de risque fondĂ©e sur un prix constant du risque des facteurs. Dans les deux cas, l'identification du modĂšle est obtenue Ă partir de restrictions sur les moments conditionnels, ce qui permet l'estimation par variables instrumentales. Une Ă©tape prĂ©liminaire de dĂ©termination du nombre de facteurs et d'identification de portefeuilles reprĂ©sentatifs est proposĂ©e. Elle est fondĂ©e sur une sĂ©quence de tests de sur-identification qui englobe les tests de caractĂ©ristiques communes d'Engle et Kozicki (1993).asset pricing, stochastic volatility, conditional factor models, multivariate conditional heteroskedasticity, common features, multiperiod conditional moment restrictions, Generalized Method of Moments., Ă©valuation d'actifs financiers, volatilitĂ© stochastique, modĂšles conditionnels Ă facteurs, hĂ©tĂ©roscĂ©dasticitĂ© conditionnelle multivariĂ©e, caractĂ©ristiques communes, restrictions de moments conditionnels avec retards, MĂ©thode des Moments GĂ©nĂ©ralisĂ©s
Transforming Maineâs Economy: Innovation and Entrepreneurship Policy
Innovation and entrepreneurship are major drivers of economic growth. Support for them is a primary role of state government in order to increase the well being of its citizens through the provision of well-paying jobs that cannot be easily exported. Today, the stateâs role is described as âenhancing the innovation ecosystem,â with the goal of increased productivity, innovation and competitiveness. Policies to build the ecosystem include: (1) building and supporting a stateâs research and development capacity; (2) encouraging a stateâs entrepreneurial community, (3) increasing the productivity of a stateâs economy though the commercialization of new products, services, processes, business models and marketing strategies and (4) supporting sectors and/or clusters. Each of these is part of an overall policy environment that will support innovation and entrepreneurship
« Sur la carte de lâĂąme allemande, une tache blanche », le passĂ© de lâAllemagne vu au prĂ©sent de la troisiĂšme gĂ©nĂ©ration
Les trois jeunes auteurs (nĂ©s en 1965, 1968, 1974) ne se posent plus la question de la culpabilitĂ© mais celle du souvenir, celle du vĂ©cu, par delĂ le long silence des gĂ©nĂ©rations prĂ©cĂ©dentes. Seul le sentiment de ce vĂ©cu leur permettra de trouver leur place dans la lignĂ©e des gĂ©nĂ©rations. Il nây a pas prescription, le passĂ© est partie intĂ©grante des plus jeunes aussi, mais lâHistoire transmet autre chose que la mĂ©moire; Ainsi, les grands-parents sont-ils soumis au questionnement (DĂŒckers / Beyer), ou si ce ne sont eux, leur gĂ©nĂ©ration (Amend) ou alors, lâauteur se livre Ă une reconstitution par la fiction, de la rĂ©alitĂ© dâalors (Beyer). Ces trois auteurs se situent Ă lâopposĂ© du monde mĂ©diatique qui a choisi de se focaliser sur lâanecdote et, grĂące Ă la distance historique, ils ouvrent ainsi de nouvelles possibilitĂ©s Ă la littĂ©rature.Die drei jungen Autoren (1965, 1968, 1974 geboren) stellen sich nicht mehr die Schuldfrage sondern die der Erinnerung, die der erlebten Wirklichkeit ĂŒber die langjĂ€hrige Verschwiegenheit der vorigen Generationen hinĂŒber. Allein das GefĂŒhl dieser Erlebnisse wird möglich machen, dass die JĂŒngeren ihren Platz in der Reihenfolge der Generationen finden. Es gibt keine VerjĂ€hrung, die Vergangenheit ist Teil auch der JĂŒngeren, aber Geschichte vermittelt Anderes als Erinnerung, so werden die GroĂeltern (DĂŒckers / Beyer) â oder deren Generation (Amend) â abgefragt oder die damalige Gegenwart fiktional rekonstruiert (Beyer). Am entgegengesetzten Pol der Medienwelt und deren Fixierung aufs Anekdotische, finden die drei Autoren den Weg zu einer anderen Auffassung der deutschen Geschichte, der historische Abstand ist hier am Werk und öffnet neue Möglichkeiten in der Literatur
Histoire et tabous : une imposture dâĂtat.OĂč comment Christa Wolf et Christoph Hein avaient entrepris de dĂ©jouer lâimposture de lâHistoire officielle en RDA
On peut considĂ©rer le rapport Ă lâHistoire comme un indice de lâĂ©tat dâune sociĂ©tĂ©. Ici, câest le rapport que la RDA entretenait avec lâHistoire qui est au centre de la notion dâimposture. Les ouvrages historiques, quâils soient ou non destinĂ©s Ă lâenseignement, nous montrent Ă quels niveaux se situe lâimposture, celui de la mise en avant dâĂ©lĂ©ments au dĂ©triment dâautres, celui de lâignorance dĂ©libĂ©rĂ©e, celui de causalitĂ©s que lâHistoire rend improbables. Face Ă cette construction factice affluent les souvenirs et le vĂ©cu de la population qui a la mĂ©moire des traumatismes subis. Christa Wolf et Christoph Hein remettent en scĂšne leurs propres souvenirs pour redonner une consistance et une dignitĂ©, mais aussi une image plus conforme Ă la rĂ©alitĂ© de ce que fut leur jeunesse. Nazisme et stalinisme sont dĂ©crits dans Trame dâenfance et dans La fin de Horn comme des Ă©lĂ©ments constitutifs de lâidentitĂ© est-allemande.Als Indikator des Zustands einer Gesellschaft spielt das VerhĂ€ltnis, das sie zur Geschichte pflegt, eine wichtige Rolle. Hier steht das VerhĂ€ltnis des Staates zur Geschichte in der DDR im Mittelpunkt des Begriffs « Betrug ». DDR-GeschichtsbĂŒcher, ob zum Unterricht bestimmt oder nicht, zeigen auf welcher Ebene der Betrug liegt : gewisse AblĂ€ufe werden in den Vordergrund gestellt, andere werden schlicht ignoriert, andere sind inzwischen von der Geschichte als irrelevant erklĂ€rt worden. Diesem trĂŒgerischen Konstrukt gegenĂŒber erinnert sich die DDR-Bevölkerung an die erlebten Traumata. Christa Wolf und Christoph Hein bearbeiten ihre eigenen Erfahrungen und Erinnerungen, um von ihrer Jugend ein echteres und volleres Bild zu geben. Nazismus und Stalinismus sind in Horns Ende und Kindheitsmuster als Teile einer Bestandsaufnahme der DDR-IdentitĂ€t aufgefaĂt
Sustainability and Workforce Development in Maine
Maine is facing challenges in terms of its workÂforce: education levels lag behind those in the other New England states; population growth is slow; and the economy is undergoing a change that has shifted from manufacturing to more knowledge-based jobs. Catherine Renault, Linda Silka and Jake Ward discuss these challenges, looking at what employers want in their employees and at the kinds of jobs the state is likely to see in the future. They point out that the Sustainability Solutions Initiative, with its emphasis on a boundary-crossing approach to educaÂtion, is an example of a way to train todayâs students to fill and create the jobs of the future
Static and dynamic behaviour of a 3D periodic structure
This contribution deals with the assessment of static and dynamic behavior a 3D-periodic structure. Equivalent Young and shear moduli are evaluated respectively via a spring-network calculation performed on a representative volume element (RVE)of the structure and an energy approach. To assess the accuracy of the two methods, FE simulations are performed, and tensile experiments are conducted on specimens cut out from 3D-structure panels. Results show disagreement for stiffness values along y-direction. This is thought to be due to stiffness variation between RVE's due to boundary conditions. A new analytical/numerical approach is proposed taking into consideration the presence of different types of boundary conditions on RVE's. Static results are further used as an input for FE investigations of the dynamic behavior of the structure. Two models are proposed: a) homogeneous and b) laminated models. Vibration tests are performed on different specimens and fundamental frequencies are noted. Results for both models correlate well with experimental data. However, the homogeneous model is limited to low frequencies
Reconstruction of directed neuronal networks in a microfluidic device with asymmetric microchannels
International audienceMicrofluidic devices for controlling neuronal connectivity in vitro are extremely useful tools for deciphering pathological and physiological processes occurring in neuronal networks. These devices allow the connection between different neuronal populations located into separate culture chambers through axon-selective microchannels. In order to implement specific features of brain connectivity such as directionality, it is necessary to control axonal growth orientation in these devices. Among the various strategies proposed to achieve this goal, one of the most promising and easily reproducible is the use of asymmetric microchannels. We present here a general protocol and several guidelines for the design, production and testing of a new paradigm of asymmetric microchannels geometries based on a âreturn to senderâ strategy. In this method, axons are either allowed to travel between the emitting and receiving chambers within straight microchannels (forward direction), or are rerouted toward their initial location through curved microchannels (reverse direction). We introduce variations of these âarchesâ microchannels and evaluate their respective axonal filtering capacities. Importantly, one of these variants presents an almost complete filtration of axonal growth in the non-permissive direction while allowing robust axonal invasion in the other one, with a selectivity ratio as high as 99.7%
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