The potential of discs from a "mean Green function"

By using various properties of the complete elliptic integrals, we have derived an alternative expression for the gravitational potential of axially symmetric bodies, which is free of singular kernel in contrast with the classical form. This is mainly a radial integral of the local surface density weighted by a regular "mean Green function" which depends explicitly on the body's vertical thickness. Rigorously, this result stands for a wide variety of configurations, as soon as the density structure is vertically homogeneous. Nevertheless, the sensitivity to vertical stratification | the Gaussian profile has been considered | appears weak provided that the surface density is conserved. For bodies with small aspect ratio (i.e. geometrically thin discs), a first-order Taylor expansion furnishes an excellent approximation for this mean Green function, the absolute error being of the fourth order in the aspect ratio. This formula is therefore well suited to studying the structure of self-gravitating discs and rings in the spirit of the "standard model of thin discs" where the vertical structure is often ignored, but it remains accurate for discs and tori of finite thickness. This approximation which perfectly saves the properties of Newton's law everywhere (in particular at large separations), is also very useful for dynamical studies where the body is just a source of gravity acting on external test particles.Comment: Accepted for publication in MNRAS, 11 page

Orally available Mn porphyrins with superoxide dismutase and catalase activities

Superoxide dismutase/catalase mimetics, such as salen Mn complexes and certain metalloporphyrins, catalytically neutralize reactive oxygen and nitrogen species, which have been implicated in the pathogenesis of many serious diseases. Both classes of mimetic are protective in animal models of oxidative stress. However, only AEOL11207 and EUK-418, two uncharged Mn porphyrins, have been shown to be orally bioavailable. In this study, EUK-418 and several new analogs (the EUK-400 series) were synthesized and shown to exhibit superoxide dismutase, catalase, and peroxidase activities in vitro. Some also protected PC12 cells against staurosporine-induced cell death. All EUK-400 compounds were stable in simulated gastric fluid, and most were substantially more lipophilic than the salen Mn complexes EUK-189 and EUK-207, which lack oral activity. Pharmacokinetics studies demonstrate the presence of all EUK-400 series compounds in the plasma of rats after oral administration. These EUK-400 series compounds are potential oral therapeutic agents for cellular damage caused by oxidative stress

Model Risk Management. Le prassi e il modello a tendere.

I modelli hanno assunto un ruolo pervasivo nell’operatività bancaria configurandosi come driver essenziali nel decision making sia in ambito regolamentare che gestionale, e questa considerazione, seppur con caratterizzazioni diverse, risulta valida sia per banche “significant” che “less significant”. Si evidenzia che il numero e la complessità dei modelli hanno raggiunto un livello di ampiezza tale da richiederne una gestione dedicata e strumenti specifici per evitare che la base decisionale si poggi su algoritmi, dati o elaborazioni non adeguati. Oltre alla complessità intrinseca dei modelli, si aggiunge una crescente interconnessione tra gli stessi per cui le criticità di un modello possono riverberarsi sui modelli collegati con effetti poco prevedibili. Le mutevoli condizioni di contesto (accentuate dall’emergenza Covid), hanno ulteriormente amplificato l’esigenza di ridurre la distanza tra l’identificazione delle criticità sui modelli, la presa in carico delle azioni correttive, il relativo monitoraggio e il rilascio degli interventi. Una catena di trasmissione non adeguata comporta inevitabilmente tempi di risposta più lunghi, con modelli che non sono in grado di rappresentare adeguatamente il contesto operativo

Predicting default probabilities and implementing trading strategies for emerging markets bond portfolios

In this paper we address two main issues: the computation of default probability implicit in emerging markets bond prices and the impact on portfolio risks and returns of expected changes in default probability. Using a reduced-form model, weekly estimates of default probabilities for US Dollar denominated Global bonds of twelve emerging markets are extrapolated for the sample period 1997-2001. The estimation of a logit type econometric model shows that weekly changes of the default probabilities can be explained by means of some capital markets factors. Recursively estimating the logit model using rolling windows of data, out-of-sample forecasts for the dynamics of default probabilities are generated and used to form portfolios of bonds. The practical application provides interesting results, both in terms of testing the ability of a naive trading strategy based on model forecasts to outperform a \u201dcustomized benchmark\u201d, and in terms of the model ability to actively manage the portfolio risk (evaluated in terms of VaR) with respect to a constant proportion allocation

Finite element models of rock samples electrical responses under geothermal thermo-baric conditions

Budapest, Hungar

Resistivity changes related to microcracks produced by rock internal fluid pressure at different thermo-baric conditions: laboratory experiments and numerical model

Copenhagen, D