Tidal Effects on the Habitability of Exoplanets: The Case of GJ 581 d

Tides may be crucial to the habitability of exoplanets. If such planets form around low-mass stars, then those in the circumstellar habitable zone will be close enough to their host stars to experience strong tidal forces. Tides may result in orbital decay and circularization, evolution toward zero obliquity, a fixed rotation rate (not necessarily synchronous), and substantial internal heating. Due to tidal effects, the range of habitable orbital locations may be quite different from that defined by the traditional concept of a habitable zone (HZ) based on stellar insolation, atmospheric effects, and liquid water on a planet's surface. Tidal heating may make locations within the traditional HZ too hot, while planets outside the traditional zone could be rendered quite habitable due to tides. Here we consider these effects on the exoplanet GJ 581 d.Comment: 2 pages, 1 figure

Quantitatively consistent computation of coherent and incoherent radiation in particle-in-cell codes - a general form factor formalism for macro-particles

Quantitative predictions from synthetic radiation diagnostics often have to consider all accelerated particles. For particle-in-cell (PIC) codes, this not only means including all macro-particles but also taking into account the discrete electron distribution associated with them. This paper presents a general form factor formalism that allows to determine the radiation from this discrete electron distribution in order to compute the coherent and incoherent radiation self-consistently. Furthermore, we discuss a memory-efficient implementation that allows PIC simulations with billions of macro-particles. The impact on the radiation spectra is demonstrated on a large scale LWFA simulation.Comment: Proceedings of the EAAC 2017, This manuscript version is made available under the CC-BY-NC-ND 4.0 licens

Asymmetric Smiles, Leverage Effects and Structural Parameters

In this paper, we characterize the asymmetries of the smile through multiple leverage effects in a stochastic dynamic asset pricing framework. The dependence between price movements and future volatility is introduced through a set of latent state variables. These latent variables can capture not only the volatility risk and the interest rate risk which potentially affect option prices, but also any kind of correlation risk and jump risk. The standard financial leverage effect is produced by a cross-correlation effect between the state variables which enter into the stochastic volatility process of the stock price and the stock price process itself. However, we provide a more general framework where asymmetric implied volatility curves result from any source of instantaneous correlation between the state variables and either the return on the stock or the stochastic discount factor. In order to draw the shapes of the implied volatility curves generated by a model with latent variables, we specify an equilibrium-based stochastic discount factor with time non-separable preferences. When we calibrate this model to empirically reasonable values of the parameters, we are able to reproduce the various types of implied volatility curves inferred from option market data.Dans cet article, nous caractérisons les asymétries observées dans les courbes de volatilités implicites par la présence d'effets de levier multiples dans un modèle dynamique stochastique d'évaluation des actifs financiers. La dépendance entre les mouvements de prix et la volatilité future est introduite par l'intermédiaire d'un ensemble de variables d'état latentes. Ces variables d'état sont susceptibles de capter non seulement le risque de volatilité et le risque de taux d'intérêt qui peuvent influer sur les prix d'options, mais encore les risques de corrélation et de saut. L'effet de levier financier traditionnel est produit quant à lui par une corrélation instantanée entre les variables d'état qui entrent dans le processus de volatilité stochastique du prix de l'action et le processus du prix de l'action proprement dit. Nous disposons toutefois d'un cadre plus général dans lequel l'asymétrie des courbes de volatilités implicites résulte de toute corrélation instantanée entre les variables d'état et soit le rendement de l'action soit le facteur d'actualisation stochastique. Dans le but de tracer les formes des courbes de volatilités implicites générées par un modèle avec variables latentes, nous spécifions un facteur d'actualisation stochastique fondé sur un modèle d'équilibre avec préférences non séparables dans le temps. Lorsque nous calibrons ce modèle avec des valeurs raisonnables des paramètres, nous reproduisons les diverses formes de courbes de volatilités implicites qui sont produites à partir des données de prix d'options observées sur le marché

Adicción a los Videojuegos: ¿Qué podemos aprender desde la perspectiva de la neurociencia de la comunicación?

In recent years, video game addiction has received considerable empirical attention. Unfortunately, this research is stymied by inconsistencies in both conceptual and operational definitions of video game addiction. Moreover, the use of several video game addiction scales makes it difficult to estimate the prevalence and potential effects of video game addiction. While game genre is often treated as a predictor of video game addiction, existing measures often downplay the structural and social characteristics of video games that may contribute to behavioral outcomes such as increased playing time and addiction. In an effort to provide the clarity necessary to overcome these issues, we review research on video game addiction with a focus on the largely ignored unique characteristics of video games that are crucial for a more complete conceptualization of video game addiction. With this review in mind, we offer a conceptual framework for the integration of video game addiction within the broader context of behavioral addictions. Finally, we consider the neurological foundation of addiction and suggest opportunities for media neuroscientists to increase understanding and prediction of video game addiction and explore how game content features interact with reward systems in the brain.En los últimos años, la adicción a los videojuegos ha recibido una atención empírica considerable. Desafortunadamente, la investigación en este campo se encuentra obstaculizada por inconsistencias en definiciones conceptuales y operacionales de la adicción a los videojuegos. Por otro lado, el uso de varias escalas de adicción a los videojuegos dificulta la estimación de la prevalencia y los efectos potenciales de la adicción a los videojuegos. Mientras el género del juego es considerado frecuentemente como un predictor de la adicción a los videojuegos, las medidas existentes restan importancia a las características sociales y estructurales de los videojuegos que pueden contribuir a resultados conductuales tales como un incremento en el tiempo de juego y adicción. En un esfuerzo por proveer de claridad necesaria para subsanar estos problemas, se realiza una revisión sobre investigaciones relacionadas a la adicción a los videojuegos con un enfoque en las características de los videojuegos extensamente ignoradas y que son cruciales para una conceptualización más completa acerca de la adicción a los videojuegos. Con esta revisión, ofrecemos un marco conceptual para la integración de la adicción a los videojuegos dentro un contexto más amplio como el de las adicciones conductuales. Finalmente, consideramos la base neurológica de la adicción y sugerimos oportunidades para los neurocientíficos de la comunicación con el objetivo de incrementar la comprensión y predicción de la adicción a los videojuegos y explorar cómo los elementos de un juego interactúan con los sistemas de recompensa en el cerebro

Empirical Assessment of an Intertemporal Option Pricing Model with Latent variables

This paper assesses the empirical performance of an intertemporal option pricing model with latent variables which generalizes the Hull-White stochastic volatility formula. Using this generalized formula in an ad-hoc fashion to extract two implicit parameters and forecast next day S&P 500 option prices, we obtain similar pricing errors than with implied volatility alone as in the Hull-White case. When we specialize this model to an equilibrium recursive utility model, we show through simulations that option prices are more informative than stock prices about the structural parameters of the model. We also show that a simple method of moments with a panel of option prices provides good estimates of the parameters of the model. This lays the ground for an empirical assessment of this equilibrium model with S&P 500 option prices in terms of pricing errors.On évalue dans cet article la performance empirique d’un modèle dynamique d’évaluation d’options qui fournit une formule de prix fondée sur des processus latents de variables d’état. Cette formule est une généralisation de la formule dite de Hull et White (1987) qui évalue une option européenne écrite sur un actif à volatilité stochastique. On propose dans un premier temps de fonder sur cette formule une procédure empirique ad hoc permettant l’évaluation d’une option à partir du calcul de deux paramètres implicites extraits sur les prix d’options observés la veille. Appliquée à la prévision des prix d’options sur l’indice S&P 500, cette procédure offre un gain de précision significatif par rapport à la pratique usuelle de prévision des prix à travers une volatilité implicite conformément à ce que suggère la formule de Hull et White. Dans un second temps, on propose de particulariser le modèle dans un contexte d’équilibre intertemporel avec utilité récursive. On fournit alors des résultats d’expériences de Monte Carlo montrant que les statistiques de prix d’options produisent des estimateurs des paramètres structurels de l’équilibre beaucoup plus précis que les données de prix de l’actif sous-jacent. Ceci suggère en retour que les paramètres structurels devraient jouer un rôle important dans l’évaluation d’options. Cette affirmation est validée empiriquement sur les données d’options sur l’indice S&P 500 en montrant que la formule de Hull et White est dominée, en termes de prévision des prix d’options hors-échantillon par une formule dépendant explicitement de paramètres de préférence, a fortiori si ceux-ci prennent en compte de façon non contrainte à la fois l’aversion pour le risque et l’élasticité de substitution intertemporelle

Chateaubriand\u27s Travels in America

Chateaubriand’s Travels in America, presented here in its first modern translation, was a reflection of the attitudes of his epoch toward the New World. And at the same time, because of his enormous literary reputation, it has continued to be a major source of European impressions about America. The America portrayed by Chateaubriand was much more a product of his reading and his imagination than of his actual visit. (His supposed itinerary included a trip up the Hudson to Albany, a visit to Niagara Falls via the Mohawk Trail, a trip down the Mississippi to the Natchez country, and even a visit to the Carolinas and the southern tip of Florida). Though the Frenchman of the nineteenth century could have obtained a much truer picture of America in any number of realistic works, he still chose the poetic evocation of Chateaubriand because he shared the same temperament, the same prejudices, and the same particular view of the world. Richard Switzer is chairman of the department of French and Italian at the University of Wisconsin.https://uknowledge.uky.edu/upk_united_states_history/1083/thumbnail.jp

School adjustment and substance use in early adolescent boys: association with paternal alcoholism with and without dad in the home

The present study examined the association of paternal alcoholism with early adolescent boys’ school adjustment and substance use, and its moderation by paternal absence, controlling for parents’ socioeconomic resources. A community sample of 653 urban, low socioeconomic status (SES) families from Montreal, Canada, was assessed and information collected from parents, teachers, and adolescents’ self-reports, and school records. Paternal alcoholism was significantly associated with boys’ lower academic performance, lower grades, higher frequency of tobacco, marijuana and hard drugs use, of getting drunk, and using a variety of hard drugs. However, the separation from the alcoholic father represented a significant factor of moderation in regard to boys’ substance use: Sons of alcoholic fathers living with their dad in intact families were more likely to use tobacco and marijuana, to get drunk, and to use a variety of hard drugs than their peers not living with their alcoholic father, whether in single-mother or stepfamilies