Bayesian nonparametric sparse VAR models

High dimensional vector autoregressive (VAR) models require a large number of parameters to be estimated and may suffer of inferential problems. We propose a new Bayesian nonparametric (BNP) Lasso prior (BNP-Lasso) for high-dimensional VAR models that can improve estimation efficiency and prediction accuracy. Our hierarchical prior overcomes overparametrization and overfitting issues by clustering the VAR coefficients into groups and by shrinking the coefficients of each group toward a common location. Clustering and shrinking effects induced by the BNP-Lasso prior are well suited for the extraction of causal networks from time series, since they account for some stylized facts in real-world networks, which are sparsity, communities structures and heterogeneity in the edges intensity. In order to fully capture the richness of the data and to achieve a better understanding of financial and macroeconomic risk, it is therefore crucial that the model used to extract network accounts for these stylized facts.Comment: Forthcoming in "Journal of Econometrics" ---- Revised Version of the paper "Bayesian nonparametric Seemingly Unrelated Regression Models" ---- Supplementary Material available on reques

Will a Black Hole Soon Emerge from SN 1997D ?

Observations combined with theoretical modeling of the light curve of the recently discovered supernova 1997D in NGC 1536 suggest that it might host a black hole formed in the aftermath of the explosion. We consider some observable consequences of a black hole in SN 1997D and estimate the late--time accretion luminosity of the material which falls back onto the hole. We find that this luminosity, decaying with a characteristic power--law dependence on time, may emerge above the emission of the envelope in just a few years. Its detection would thus provide unmistakable evidence for the presence of a black hole.Comment: 8 pages, LaTeX, aaspp4.sty style file (AASTEX package), 2 postscript figures (included). To appear in The Astrophysical Journal Letters (scheduled for August 1, 1998 issue, Vol. 502

Settis, Koolhaas e l’architettura del futuro del classico. Per una nuova gipsoteca: due mostre alla Fondazione Prada a Milano e Venezia

The recent double exhibition “Serial/Portable Classic” opened in the new beautiful spaces of the Fondazione Prada in Milano and in Venezia suggests a re-assessment on the theme of the architecture of the Gipsoteca. There is a renewed interest around the plaster cast collections, not merely as museum, but with an experimental and laboratorial meaning. This exhibition indicates a new way (both contextual and European) for a rebirth of the architecture for a contemporary Gipsoteca Milanese

A flexible space-variant anisotropic regularisation for image restoration with automated parameter selection

We propose a new space-variant anisotropic regularisation term for variational image restoration, based on the statistical assumption that the gradients of the target image distribute locally according to a bivariate generalised Gaussian distribution. The highly flexible variational structure of the corresponding regulariser encodes several free parameters which hold the potential for faithfully modelling the local geometry in the image and describing local orientation preferences. For an automatic estimation of such parameters, we design a robust maximum likelihood approach and report results on its reliability on synthetic data and natural images. For the numerical solution of the corresponding image restoration model, we use an iterative algorithm based on the Alternating Direction Method of Multipliers (ADMM). A suitable preliminary variable splitting together with a novel result in multivariate non-convex proximal calculus yield a very efficient minimisation algorithm. Several numerical results showing significant quality-improvement of the proposed model with respect to some related state-of-the-art competitors are reported, in particular in terms of texture and detail preservation

Spherical Accretion onto Neutron Stars Revisited: Are Hot Solutions Possible ?

Stationary, spherical accretion onto an unmagnetized neutron star is here reconsidered on the wake of the seminal paper by Zel'dovich \& Shakura (1969). It is found that new ``hot'' solutions may exist for a wide range of luminosities. These solutions are characterized by a high temperature, $10^{9}\div 10^{11}$ K, and arise from a stationary equilibrium model where the dominant radiative mechanisms are multiple Compton scattering and bremsstrahlung emission. For low luminosities, \mincir 10^{-2} \ L_{E}, only the ``cold'' (\`a la Zel'dovich and Shakura) solution is present.Comment: 11 pages (3 postscript files figures available on request), PlainTeX, Ref. SISSA 21/94/

Reinke’s crystals in perivascular and peritubular Leydig cells of men with nonobstructive and obstructive azoospermia: a retrospective case-control study

Aim To analyze the differences in the population of perivascular and peritubular Leydig cells (LC) and the number of Reinke’s crystals (RCs) in the testicles of infertile men with non-obstructive and obstructive azoospermia. Methods This retrospective case-control study was conducted on the testicle tissue of infertile men with obstructive (n = 10) and those with non-obstructive azoospermia (n = 100). Stereological analysis was performed on 7-μm paraffin sections. Measurements were carried out by using the Weibel multipurpose test system. Results Patients with non-obstructive azoospermia had a higher total/absolute number of LCs in the perivascular space (P = 0.034). In these patients, no significant difference was found in the total and absolute number of RCs between the peritubular and perivascular space. Patients with obstructive azoospermia had around three times higher absolute number of RCs in both the peritubular and perivascular spaces (P = 0.002; P < 0.001) than non-obstructive group. Conclusion Our results suggest that in patients with nonobstructive azoospermia LCs migrated or had different densities in the peritubular and perivascular space compared with patients with obstructive azoospermia. Moreover, the lower number of RCs could imply their utilization by LCs in testosterone production

HEBE: Highly Engaging eBook Experiences

Despite more and more books are made available in electronic format and technology is increasingly present in children’s everyday life, thus far the potential of the electronic book (eBook) medium has been only partially exploited. With the Highly Engaging eBook Experiences (HEBE) project we studied how to design and evaluate eBooks for children with the goal of making the reading experience more engaging. The project began with an investigation of the many facets that characterize the reading experience of children in order to understand how it could possibly be enhanced by electronic books. In a later stage an intergenerational design team used different techniques of Cooperative Inquiry to explore a range of design ideas. Then, based on those ideas, we developed a prototype of enhanced eBook and elaborated a shortlist of design recommendations that are intended to help designers in creating more engaging eBooks. The research project ended with a stage of evaluation where children’s User Experience with the eBook prototype was assessed. We took inspiration from Csikszentmihalyi’s Flow theory to define a benchmark for evaluating the reading experience. Then, by means of the Experience Sampling Method (ESM), we investigated and collected data on the reading experience of two groups of children, one of which read an eBook enhanced following our design recommendations while the other read a basic version of the same eBook. Following a mixed-method approach, with quantitative analysis we verified whether participants who read the enhanced eBook had a better reading experience, while with qualitative analysis we tried to understand why. The results of the evaluation showed that that an eBook designed following our design recommendations may have a positive effect on children’s reading experience by making it more engaging