Face amplitude of spinfoam quantum gravity

The structure of the boundary Hilbert-space and the condition that amplitudes behave appropriately under compositions determine the face amplitude of a spinfoam theory. In quantum gravity the face amplitude turns out to be simpler than originally thought.Comment: 5 pages, 2 figure

An anatomy of industry merger waves

We propose a novel panel Bayesian Markov regime-switching Poisson regression model with time-varying transition probabilities to test existing theories on the driving forces of wave-like patterns in same-industry mergers and acquisitions. We show that the dynamics and persistence of merger waves change substantially in the cross-section of deal flow. This suggests that any inference on existing economically justified competing explanations of merger waves at the aggregate market level could be misleading, as the observed cross-industry heterogeneity in waves is shown to be the consequence of different responses to common or distinct drivers of merger activity

The dynamics of expected returns: evidence from multi-scale time series modelling

Conventional wisdom posits that all the relevant investors' information lies at the highest possible frequency of observation, so that long-run expected returns can be mechanically inferred by a forward aggregation of short-run estimates. We reverse such logic and propose a novel framework to model and extract the dynamics of latent short-term expected returns by coherently combining the lower-frequency information embedded in multiple predictors. We show that the information cascade from low- to high-frequency levels allows to identify long-lasting effects on expected returns that cannot be captured by standard persistent ARMA processes. The empirical analysis demonstrates that the ability of the model to capture simultaneously medium- to long-term fluctuations in the dynamics of expected returns, has first order implications for forecasting and investment decisions

The dynamics of returns predictability in cryptocurrency markets

In this paper, we take a forecasting perspective and compare the information content of a set of market risk factors, cryptocurrency-specific predictors, and sentiment variables for the returns of cryptocurrencies vs traditional asset classes. To this aim, we rely on a flexible dynamic econometric model that not only features time-varying coefficients, but also allows for the entire forecasting model to change over time to capture the time variation in the exposures of major digital currencies to the predictive variables. Besides, we investigate whether the inclusion of cryptocurrencies in an already diversified portfolio leads to additional economic gains. The main empirical results suggest that cryptocurrencies are not systematically predicted by stock market factors, precious metal commodities or supply factors. On the contrary, they display a time-varying but significant exposure to investors' attention. In addition, also because of a lack of predictability compared to traditional asset classes, cryptocurrencies lead to realized expected utility gains for a power utility investor

El papel de los vínculos organizativos en las empresas virtuales. El caso de Perting SRL

El artículo analiza los vínculos organizativos recreados en los departamentos o áreas funcionales de Perting LtD, empresa virtual que desde 2001 se ha venido desarrollando en la Universidad de Bolonia. Estos vínculos se analizaron entre dichos departamentos y los profesores/tutores (vínculos educativos), entre los propios departamentos (vínculos operativos internos), y con agentes externos (vínculos operativos externos), durante el primer semestre del curso académico 2016/2017. Los resultados delatan una cierta estabilidad en la evolución de los vínculos y una prevalencia de vínculos internos. Además, en relación al feedback o tiempo de espera en la respuesta fue menor en las relaciones internas entre los departamentos de Perting que en los contactos externos

Metabolic impacts of climate change on marine ecosystems : Implications for fish communities and fisheries

Unidad de excelencia María de Maeztu MdM-2015-0552Aim:Climate change will reshape marine ecosystems over the 21st century through diverse and complex mechanisms that are difficult to assess quantitatively. Here, we characterize expectations for how marine community biomass will respond to the energetic consequences of changes in primary production and temperature-dependent metabolic rates, under a range of fishing/conservation scenarios. Location: Global ocean. Time period: 1950-2100.Major taxa studied: Commercially harvested marine ectotherms ('fish'). Methods: We use a size-structured macroecological model of the marine ecosystem, coupled with a catch model that allows for calibration with global historical data and simulation of fishing. We examine the four energetic mechanisms that, within the model framework, determine the community response to climate change: net primary production, phytoplankton cell size, and the temperature dependencies of growth and natural mortality. Results: Climate change decreases the modelled global fish community biomass by as much as 30% by 2100. This results from a diminished energy supply to upper trophic levels as photosynthesis becomes more nutrient limited and phytoplankton cells shrink, and from a temperature-driven increase of natural mortality that, together, overwhelm the effect of accelerated somatic growth rates. Ocean circulation changes drive regional variations of primary production, producing patterns of winners and losers that largely compensate each other when averaged globally, whereas decreasing phytoplankton size drives weaker but more uniformly negative changes. The climate impacts are similar across the range of conservation scenarios but are slightly amplified in the strong conservation scenarios owing to the greater role of natural mortality. Main conclusions: The spatial pattern of climate impacts is mostly determined by changes in primary production. The overall decline of community biomass is attributed to a temperature-driven increase of natural mortality, alongside an overall decrease in phytoplankton size, despite faster somatic growth. Our results highlight the importance of the competition between accelerated growth and mortality in a warming ocean

Rapid coastal deoxygenation due to ocean circulation shift in the NW Atlantic.

Global observations show that the ocean lost approximately 2% of its oxygen inventory over the last five decades 1-3, with important implications for marine ecosystems 4, 5. The rate of change varies with northwest Atlantic coastal waters showing a long-term drop 6, 7 that vastly outpaces the global and North Atlantic basin mean deoxygenation rates 5, 8. However, past work has been unable to resolve mechanisms of large-scale climate forcing from local processes. Here, we use hydrographic evidence to show a Labrador Current retreat is playing a key role in the deoxygenation on the northwest Atlantic shelf. A high-resolution global coupled climate-biogeochemistry model 9 reproduces the observed decline of saturation oxygen concentrations in the region, driven by a retreat of the equatorward-flowing Labrador Current and an associated shift toward more oxygen-poor subtropical waters on the shelf. The dynamical changes underlying the shift in shelf water properties are correlated with a slowdown in the simulated Atlantic Meridional Overturning Circulation 10. Our results provide strong evidence that a major, centennial-scale change of the Labrador Current is underway, and highlight the potential for ocean dynamics to impact coastal deoxygenation over the coming century