Partition of unity interpolation using stable kernel-based techniques

In this paper we propose a new stable and accurate approximation technique which is extremely effective for interpolating large scattered data sets. The Partition of Unity (PU) method is performed considering Radial Basis Functions (RBFs) as local approximants and using locally supported weights. In particular, the approach consists in computing, for each PU subdomain, a stable basis. Such technique, taking advantage of the local scheme, leads to a significant benefit in terms of stability, especially for flat kernels. Furthermore, an optimized searching procedure is applied to build the local stable bases, thus rendering the method more efficient

Morphology of galaxies with quiescent recent assembly history in a Lambda-CDM universe

The standard disc formation scenario postulates that disc forms as the gas cools and flows into the centre of the dark matter halo, conserving the specific angular momentum. Major mergers have been shown to be able to destroy or highly perturb the disc components. More recently, the alignment of the material that is accreted to form the galaxy has been pointed out as a key ingredient to determine galaxy morphology. However, in a hierarchical scenario galaxy formation is a complex process that combines these processes and others in a non-linear way so that the origin of galaxy morphology remains to be fully understood. We aim at exploring the differences in the formation histories of galaxies with a variety of morphology, but quite recent merger histories, to identify which mechanisms are playing a major role. We analyse when minor mergers can be considered relevant to determine galaxy morphology. We also study the specific angular momentum content of the disc and central spheroidal components separately. We used cosmological hydrodynamical simulations that include an effective, physically motivated supernova feedback that is able to regulate the star formation in haloes of different masses. We analysed the morphology and formation history of a sample of 15 galaxies of a cosmological simulation. We performed a spheroid-disc decomposition of the selected galaxies and their progenitor systems. The angular momentum orientation of the merging systems as well as their relative masses were estimated to analyse the role played by orientation and by minor mergers in the determination of the morphology. We found the discs to be formed by conserving the specific angular momentum in accordance with the classical disc formation model. The specific angular momentum of the stellar central spheroid correlates with the dark matter halo angular momentum and determines a power law. AbridgedComment: 10 pages, 9 figures, A&A in pres

The host galaxies of long-duration GRBs in a cosmological hierarchical scenario

We developed a Monte Carlo code to generate long-duration gamma ray burst (LGRB) events within cosmological hydrodynamical simulations consistent with the concordance model. As structure is assembled, LGRBs are generated in the substructure that formed galaxies today. We adopted the collapsar model so that LGRBs are produced by single, massive stars at the final stage of their evolution. We found that the observed properties of the LGRB host galaxies (HGs) are reproduced if LGRBs are also required to be generated by low metallicity stars. The low metallicity condition imposed on the progenitor stars of LGRBs selects a sample of HGs with mean gas abundances of 12 + log O/H \~ 8.6. For z<1 the simulated HGs of low metallicity LGRB progenitors tend to be faint, slow rotators with high star formation efficiency, compared with the general galaxy population, in agreement with observations. At higher redshift, our results suggest that larger systems with high star formation activity could also contribute to the generation of LGRBs from low metallicity progenitors since the fraction of low metallicity gas available for star formation increases for all systems with look-back time. Under the hypothesis of our LGRB model, our results support the claim that LGRBs could be unbiased tracers of star formation at high redshifts.Comment: Final revised version with minor changes. 9 pages, 9 figures, mn2e.cls. To appear in MNRA

Intrinsic electric field effects on few-particle interactions in coupled GaN quantum dots

We study the multi-exciton optical spectrum of vertically coupled GaN/AlN quantum dots with a realistic three-dimensional direct-diagonalization approach for the description of few-particle Coulomb-correlated states. We present a detailed analysis of the fundamental properties of few-particle/exciton interactions peculiar of nitride materials. The giant intrinsic electric fields and the high electron/hole effective masses give rise to different effects compared to GaAs-based quantum dots: intrinsic exciton-exciton coupling, non-molecular character of coupled dot exciton wavefunction, strong dependence of the oscillator strength on the dot height, large ground state energy shift for dots separated by different barriers. Some of these effects make GaN/AlN quantum dots interesting candidates in quantum information processing.Comment: 23 pages, 8 figures, 1 tabl

Intrinsic electric field effects on few-particle interactions in coupled GaN quantum dots

We study the multiexciton optical spectrum of vertically coupled GaN/AlN quantum dots with a realistic three-dimensional direct-diagonalization approach for the description of few-particle Coulomb-correlated states. We present a detailed analysis of the fundamental properties of few-particle/ exciton interactions peculiar of nitride materials. The giant intrinsic electric fields and the high electron/ hole effective masses give rise to different effects compared to GaAs-based quantum dots: intrinsic exciton-exciton coupling, non molecular character of coupled dot exciton wave function, strong dependence of the oscillator strength on the dot height, large ground-state energy shift for dots separated by different barriers. Some of these effects make GaN/AlN quantum dots interesting candidates in quantum information processing

Low delta-V near-Earth asteroids: A survey of suitable targets for space missions

In the last decades Near-Earth Objects (NEOs) have become very important targets to study, since they can give us clues to the formation, evolution and composition of the Solar System. In addition, they may represent either a threat to humankind, or a repository of extraterrestrial resources for suitable space-borne missions. Within this framework, the choice of next-generation mission targets and the characterisation of a potential threat to our planet deserve special attention. To date, only a small part of the 11,000 discovered NEOs have been physically characterised. From ground and space-based observations one can determine some basic physical properties of these objects using visible and infrared spectroscopy. We present data for 13 objects observed with different telescopes around the world (NASA-IRTF, ESO-NTT, TNG) in the 0.4 - 2.5 um spectral range, within the NEOSURFACE survey (http://www.oa-roma.inaf.it/planet/NEOSurface.html). Objects are chosen from among the more accessible for a rendez-vous mission. All of them are characterised by a delta-V (the change in velocity needed for transferring a spacecraft from low-Earth orbit to rendez-vous with NEOs) lower than 10.5 km/s, well below the Solar System escape velocity (12.3 km/s). We taxonomically classify 9 of these objects for the first time. 11 objects belong to the S-complex taxonomy; the other 2 belong to the C-complex. We constrain the surface composition of these objects by comparing their spectra with meteorites from the RELAB database. We also compute olivine and pyroxene mineralogy for asteroids with a clear evidence of pyroxene bands. Mineralogy confirms the similarity with the already found H, L or LL ordinary chondrite analogues.Comment: 9 pages, 7 figures, to be published in A&A Minor changes by language edito

Differences in telomere length between sporadic and familial cutaneous melanoma

BACKGROUND: Several pieces of evidence indicate that a complex relationship exists between constitutional telomere length (TL) and the risk of cutaneous melanoma. Although the general perception is that longer telomeres increase melanoma risk, some studies do not support this association. We hypothesise that discordant data are due to the characteristics of the studied populations. OBJECTIVES: To evaluate the association of telomere length with familial and sporadic melanoma. METHODS: TL was measured by multiplex quantitative PCR in leukocytes from 310 melanoma patients according to familial/sporadic and single/multiple cancers and 216 age-matched controls. RESULTS: Patients with sporadic melanoma were found to have shorter telomeres as compared to those with familial melanoma. In addition, shorter telomeres, while tending to reduce the risk of familial melanoma regardless of single or multiple tumors, nearly trebled the risk of single sporadic melanoma. CONCLUSIONS: This is the first time that TL has been correlated to opposite effects on melanoma risk according to the presence or absence of familial predisposition. Individual susceptibility to melanoma should be taken into account when assessing the role of TL as a risk factor. This article is protected by copyright. All rights reserved

Soft Concurrent Constraint Programming

Soft constraints extend classical constraints to represent multiple consistency levels, and thus provide a way to express preferences, fuzziness, and uncertainty. While there are many soft constraint solving formalisms, even distributed ones, by now there seems to be no concurrent programming framework where soft constraints can be handled. In this paper we show how the classical concurrent constraint (cc) programming framework can work with soft constraints, and we also propose an extension of cc languages which can use soft constraints to prune and direct the search for a solution. We believe that this new programming paradigm, called soft cc (scc), can be also very useful in many web-related scenarios. In fact, the language level allows web agents to express their interaction and negotiation protocols, and also to post their requests in terms of preferences, and the underlying soft constraint solver can find an agreement among the agents even if their requests are incompatible.Comment: 25 pages, 4 figures, submitted to the ACM Transactions on Computational Logic (TOCL), zipped file