Optimization of selective laser sintering process conditions using stable sintering region approach

The optimization of process parameters represents one of the major drawbacks of selective laser sintering (SLS) technology since it is largely empirical and based on performing a series of trial-and-error builds. This approach is time con-suming, costly, and it ignores the properties of starting powders. This paper provides new results into the prediction of processing conditions starting from the material properties. The stable sintering region (SSR) approach has been applied to two different polymer-based powders: a polyamide 12 filled with chopped carbon fibers and polypropylene. This study shows that the laser exposure parameters suitable for successful sintering are in a range that is significantly smaller than the SSR. For both powders, the best combination of mechanical properties, dimensional accuracy, and porosity level are in fact, achieved by using laser energy density values placed in the middle of the SSR

Nothing is as it seems: genetic analyses on stranded fin whales unveil the presence of a fin-blue whale hybrid in the Mediterranean Sea (Balaenopteridae)

The fin whale Balaenoptera physalus is a large rorqual species occurring worldwide, mainly in temperate and subpolar zones. In contrast to many baleen whales, not all the fin whale populations show the same model of migration. In fact, migratory behaviours of this latter species range from long seasonal migration between high and low latitudes to a complete nonmigratory behaviour. A resident fin whale population was described in the Mediterranean Sea, which is also frequented by North Atlantic individuals entering through the Strait of Gibraltar in winter to feed. Between 2020 and 2021 three individuals initially identified as fin whales died along the Tyrrhenian coasts (Mediterranean Sea, Italy). Their mitochondrial DNA control region (mtDNA CR) was analysed and compared to fin whale haplotypes previously described in North Atlantic Ocean and Mediterranean Sea to identify their geographical origin. Our results show that two individuals most likely belong to the Mediterranean fin whale population, while an individual was recognised as a putative fin-blue whale hybrid (Balaenoptera physalus x Balaenoptera musculus) with a North Atlantic origin. The discovery of the first fin-blue whale hybrid in the Mediterranean Sea was confirmed by the analysis of a biparentally inherited marker, the α-lactalbumin (α-lac) nuclear gene, demonstrating that the morphological analysis alone does not allow to correctly identify hybrids, especially if intermediate characters of both parental species are not clearly distinguishable

On Phase-Type Distribution in Ruin Theory

The aim of this paper is to serve as an introduction to the use of phase-type distributions and at the same time to outline their use in ruin theory. Phase-type distributions, a particular class of matrix-exponential distributions, have the important advantage of being suitable for approximating most of other distributions as well as being mathematically tractable

On Gerber-Shiu equation with Erlang claims

In the classical Poisson risk model, we find an analytical solution of Gerber-Shiu equation when the claim size distribution is an Erlang, by mean of Laplace transform

Un procedimento di risoluzione dell’equazione integro-differenziale di Gerber-Shiu

Nell’ambito del modello classico della teoria del Rischio, con un processo dei sinistri poissoniano, troviamo una soluzione analitica dell’equazione integro-differenziale di Gerber-Shiu nell’ipotesi in cui la distribuzione delle somme a rischio sia una Erlang riconducendo il problema alla risoluzione di un’equazione differenziale

On matrix-exponential distributions in Risk Theory

In this paper, a particular class of matrix-exponential distributions is described, also with respect to its use in risk theory, namely phase-type distributions. Phase-type distributions have the important advantage of being suitable for approximating most of other distributions as well as being mathematically tractable. After a review on phase-type distributions and their properties, it is illustrated a possible use in risk theory. Modelling both interarrival claim times and individual claim sizes with this class of distributions an explicit formula for the probability of ultimate ruin is given

Ruin probability approximation for a class of renewal processes with heavy tails

This paper examines an integro-differential equation of the survival probability d(u) for a class of risk processes in which claims occur as an ordinary renewal process. Specifically, according to the model proposed by Dickson, claims are assumed to occur as an Erlang process. We determine d(u) by using an exponential claim size distribution, thus comparing the results to those obtained from the classical Cramér-Lundberg model. After having transformed the integro-differential equation into an integral equation, we find an approximate solution for d(u). We then test it in exponential cases. Furthermore, we consider the case of large claims characterized by heavy-tailed claim size distributions. The approximate solution found for d(u) also applies to certain subexponential distributions. Finally, we obtain an expression for the asymptotic behaviour of when the claim size distribution has a regularly varying tail

Stochastic Convergence of Income and Total Factor Productivity: Evidence from the Italian Regions

In this paper, we apply the non-parametric method proposed by Quah to examine convergence hypothesis for Italian regions using GDP and total factor productivity measured by the Malmquist index. Using the stochastic kernel approach, this study suggests that the measure of total factor productivity is a crucial precondition for the estimation of a region’s growth. Our results applied to the 20 Italian regions show no convergence for both GDP and TFP variables. For the GDP case, it confirms the Italian divide but for the TFP variable, it reveals the creation of three clubs. However, looking at the long-run density, it reveals that the shape of the ergodic density distribution, for the TFP, is clearly unimodal and it could imply a long-run convergence of regional productivity in Italy