Why haven't loose globular clusters collapsed yet?

We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(r_t/r_c), i.e. the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of twenty Galactic GCs with solid GMF measurements from deep HST or VLT data. All the high-concentration clusters in the sample have a steep GMF, most likely reflecting their initial mass function. Conversely, low-concentration clusters tend to have a flatter GMF implying that they have lost many stars via evaporation or tidal stripping. No GCs are found with a flat GMF and high central concentration. This finding appears counter-intuitive, since the same two-body relaxation mechanism that causes stars to evaporate and the cluster to eventually dissolve should also lead to higher central density and possibly core-collapse. Therefore, more concentrated clusters should have lost proportionately more stars and have a shallower GMF than low concentration clusters, contrary to what is observed. It is possible that severely depleted GCs have also undergone core collapse and have already recovered a normal radial density profile. It is, however, more likely that GCs with a flat GMF have a much denser and smaller core than suggested by their surface brightness profile and may well be undergoing collapse at present. In either case, we may have so far seriously underestimated the number of post core-collapse clusters and many may be lurking in the Milky Way.Comment: Four pages, one figure, accepted for publication in ApJ Letter

Greedy kernel methods for accelerating implicit integrators for parametric ODEs

We present a novel acceleration method for the solution of parametric ODEs by single-step implicit solvers by means of greedy kernel-based surrogate models. In an offline phase, a set of trajectories is precomputed with a high-accuracy ODE solver for a selected set of parameter samples, and used to train a kernel model which predicts the next point in the trajectory as a function of the last one. This model is cheap to evaluate, and it is used in an online phase for new parameter samples to provide a good initialization point for the nonlinear solver of the implicit integrator. The accuracy of the surrogate reflects into a reduction of the number of iterations until convergence of the solver, thus providing an overall speedup of the full simulation. Interestingly, in addition to providing an acceleration, the accuracy of the solution is maintained, since the ODE solver is still used to guarantee the required precision. Although the method can be applied to a large variety of solvers and different ODEs, we will present in details its use with the Implicit Euler method for the solution of the Burgers equation, which results to be a meaningful test case to demonstrate the method's features

analysis of a new class of rational rbf expansions

Abstract We propose a new method, namely an eigen-rational kernel-based scheme, for multivariate interpolation via mesh-free methods. It consists of a fractional radial basis function (RBF) expansion, with the denominator depending on the eigenvector associated to the largest eigenvalue of the kernel matrix. Classical bounds in terms of Lebesgue constants and convergence rates with respect to the mesh size of the eigen-rational interpolant are indeed comparable with those of classical kernel-based methods. However, the proposed approach takes advantage of rescaling the classical RBF expansion providing more robust approximations. Theoretical analysis, numerical experiments and applications support our findings

Idrocarburi e aree ad alta diversit\ue0 culturale e biologica: un\u2019analisi geografica in Amazzonia

Le operazioni di esplorazione ed estrazione di idrocarburi in diversi contesti geografici sono ampiamente documentate tra le attivit\ue0 antropiche di maggiore impatto sui sistemi socio-ecologici e sul cambiamento climatico, cosi come \ue8 riconosciuta la necessit\ue0 di politiche pi\uf9 efficaci e l'uso di tecnologie pi\uf9 pulite. Lo studio presentato in questo contributo mira a: 1) analizzare e mappare le interazioni tra le attivit\ue0 legate agli idrocarburi e le aree che presentano un'elevata diversit\ue0 e sensibilit\ue0 culturale e biologica; 2) Discutere proposte di criteri geografici per individuare aree unburnable, ovvero dove lasciare gli idrocarburi sottoterra. La metodologia si basa sulla costruzione di un geodatabase open source dell'area di studio, che corrisponde all'Amazzonia dell'Ecuador e alla Region amazzonica di Loreto in Per\uf9, area riconosciuta per la sua elevata diversit\ue0 ecologica e culturale. \uc8 stata condotta un\u2019analisi in ambiente QGIS delle sovrapposizioni tra gli aspetti socio-ecologici (aree protette, territori indigeni) e le attivit\ue0 di esplorazione e produzione di idrocarburi (riserve, blocchi, pozzi, oleodotti), oltre alla revisione di documenti scientifici e non su questi aspetti. Alcuni risultati dell'analisi GIS mostrano che quasi l'intera area di studio fa parte della provincia geologica del Putumayo-Oriente-Mara\uf1on, con una stima di 7290 milioni barili di petrolio equivalente sottoterra, dove le concessioni di idrocarburi coprono il 33% della superficie e si trovano circa 1780 pozzi. Le aree protette ricadenti nelle concessioni risultano essere il 18% e importanti sono anche le sovrapposizioni con i territori indigeni, evidenziando cos\uec l'urgenza di politiche pi\uf9 efficaci per garantire la sostenibilit\ue0 ambientale e sociale e la definizione di criteri geografici per individuare aree unburnable

Comparing profitability of Burlina and Holstein Friesian cattle breeds

Aim of this study was to compare profitability of Burlina and Holstein Friesian cows in northern Italy. Cow's profitability was calculated for each breed, with consideration of economic incentive programs and alternative milk pricing scenarios. The difference in annual profitability between Burlina and Holstein Friesian ranged from −€719 to −€274 per cow per year. In a low-input management level with a cow's incentive payment and a specific cheese market strategy the low milk yield of Burlina can be compensate respect to Holstein Friesian

Contribution of White Dwarfs to Cluster Masses

I present a literature search through 31 July 1997 of white dwarfs (WDs) in open and globular clusters. There are 36 single WDs and 5 WDs in binaries known among 13 open clusters, and 340 single WDs and 11 WDs in binaries known among 11 globular clusters. From these data I have calculated WD mass fractions for four open clusters (the Pleiades, NGC 2168, NGC 3532, and the Hyades) and one globular cluster (NGC 6121). I develop a simple model of cluster evolution that incorporates stellar evolution but not dynamical evolution to interpret the WD mass fractions. I augment the results of my simple model with N-body simulations incorporating stellar evolution (Terlevich 1987; de la Feunte Marcos 1996; Vesperini & Heggie 1997). I find that even though these clusters undergo moderate to strong kinematical evolution the WD mass fraction is relatively insensitive to kinematical evolution. By comparing the cluster mass functions to that of the Galactic disk, and incorporating plausibility arguments for the mass function of the Galactic halo, I estimate the WD mass fraction in these two populations. I assume the Galactic disk is ~10 Gyrs old (Winget et al. 1987; Liebert, Dahn, & Monet 1988; Oswalt et al. 1996) and that the Galactic halo is ~12 Gyrs old (Reid 1997b; Gratton et al. 1997; Chaboyer et al. 1998), although the WD mass fraction is insensitive to age in this range. I find that the Galactic halo should contain 8 to 9% (alpha = -2.35) or perhaps as much as 15 to 17% (alpha = -2.0) of its stellar mass in the form of WDs. The Galactic disk WD mass fraction should be 6 to 7% (alpha = -2.35), consistent with the empirical estimates of 3 to 7% (Liebert, Dahn, & Monet 1988; Oswalt et al. 1996). (abridged)Comment: 20 pages, uuencoded gunzip'ed latex + 3 postscrip figures, to be published in AJ, April, 199

Análise online da qualidade de produtos agro-alimentares com técnica de RMN-CPMG com pulso de refocalização de baixo ângulo.

bitstream/item/77117/1/CT111-2010.pd