1,582 research outputs found
On the predictability horizon in Impact Monitoring of Near Earth Objects
No full textThe Impact Monitoring (IM) of Near Earth Objects (NEOs) is a fundamental part of the planetary defense strategy. Current NEO IM systems (Aegis, NEODyS and Sentry) scan the Confidence Region (CR) of each observed object looking for Virtual Impactors (VIs) with a time horizon of about 100 years. This procedure is performed regardless of the uncertainty with which the orbit of the object is known, and without considering whether a scattering encounter is present in the propagation time span. In view of the likely future increase of the IM workload due to higher future NEO discovery rates, it might be more reasonable to adapt the predictability horizon of the impacts to each object, taking into account the orbit uncertainty and the close encounters experienced. In this paper we discuss the problem of estimating a reasonable predictability horizon when multiple close encounters are present and start to address the problem proposing a formal mathematical definition of scattering encounter
Powder bed irregularity and hot-spot detection in electron beam melting by means of in-situ video imaging
No full textThe electron beam melting process has been successfully applied in various sectors to produce high-value-added products. Being a hot process operating in vacuum environment with x-rays and material vaporization among by-products, in-situ sensing and monitoring presents more challenges than in laser powder bed fusion. However, an automated and robust detection of unstable process conditions represents a key capability to meet challenging qualification requirements imposed by industry. This study presents novel in-situ monitoring methods based on high spatial resolution imaging for powder bed homogeneity monitoring and high temporal resolution video-imaging for hot-spot detection, i.e., the detection of anomalous local heat accumulations
On the possible values of the orbit distance between a near-Earth asteroid and the Earth
No full textWe consider all the possible trajectories of a near-Earth asteroid (NEA), corresponding to the whole set of heliocentric orbital elements with perihelion distance q ≤ 1.3 au and eccentricity e ≤ 1 (NEA class). For these hypothetical trajectories, we study the range of the values of the distance from the trajectory of the Earth (assumed on a circular orbit) as a function of selected orbital elements of the asteroid. The results of this geometric approach are useful to explain some aspects of the orbital distribution of the known NEAs. We also show that the maximal orbit distance between an object in the NEA class and the Earth is attained by a parabolic orbit, with apsidal line orthogonal to the ecliptic plane. It turns out that the threshold value of q for the NEA class (qmax = 1.3 au) is very close to a critical value, below which the above result is not valid
Social influences on the food preferences of house mice (Mus musculus)
No full textIn a series of studies undertaken to determine the conditions under which naive house mice (observers) develop preferences for foods eaten by recently-fed conspecifics (demonstrators), we found that observer mice exhibited enhanced preference for a food following interaction with either a healthy or an ill recently-fed demonstrator that had eaten that food. We also found that house mice developed an enhanced preference for a food after exposure to an anesthetized conspecific demonstrator powdered with that food, but not after exposure to a cotton-batting, conspecific-sized surrogate powdered with the same food. Results of other studies have indicated that, for both rats and mice, the presence in a food of carbon disulfide (a substance found on the breath of rats) increases preference for a carbon-disulfide-contaminated food. taken together, the parallels between Norway rats and house mice in social learning processes suggest homologous rather than analogous systems of communication about distant foods in these two murid rodents
La ricerca della paternità deve essere ammessa. La civilistica postunitaria e le riforme del diritto di famiglia. Questioni di diritto transitorio
No full textLa norma del codice civile italiano del 1865 che prevede il divieto di indagini sulla paternità naturale costituisce una profonda innovazione, sia rispetto alla prassi giudiziaria medievale e moderna, sia rispetto alla legislazione preunitaria di primo Ottocento.
La circostanza determina un vasto dibattito dottrinale, con una forte corrente di civilisti impegnati nel chiedere una riforma del codice, ma produce anche una rilevante casistica giurisprudenziale, in relazione soprattutto alla risoluzione di questioni di diritto transitorio. Complessa in specie la situazione dei territori già appartenuti al Lombardo-Veneto e sottoposti in precedenza alla molto diversa disciplina dell’ A. B. G. B. austriac
Low solar elongation searches for NEO: a deep sky test and its implications for survey strategies
No full textThe distribution of energy perturbations at planetary close encounters
No full textOpik’s theory of close encounters allows us to deduce an analytic expression for the distribution of energy perturbations at close encounters between small bodies and planets. The derivation of this expression highlights a simple geometric structure in the plane containing the planet and
perpendicular to the unperturbed planetocentric velocity vector. The analytic formulation reproduces
well the results of the numerical integrations that first pointed out the asymmetries in the distribution of energy perturbations
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