Temperature Dependence of the Optical Response of Small Sodium Clusters

We present an analysis of the temperature dependence of the optical response of small sodium clusters in a temperature range bracketing the melting phase transition. When the temperature increases, the mean excitation energy undergoes a red shift and the plasmon is significantly broadened, in agreement with recent experimental data. We show that the single--particle levels acquire a prominent width and the HOMO--LUMO gap as well as the width of the occupied band are reduced due to large thermal cluster size and shape fluctuations. This results in a sharp increase of the static polarizability with temperature.Comment: 9 pages, Revtex, 3 uuencoded postscript figure

Weighing the IMBH candidate CO-0.40-0.22* in the Galactic Centre

The high velocity gradient observed in the compact cloud CO-0.40-0.22, at a projected distance of 60 pc from the centre of the Milky Way, has led its discoverers to identify the closeby mm continuum emitter, CO-0.40-0.22*, with an intermediate mass black hole (IMBH) candidate. We describe the interaction between CO-0.40-0.22 and the IMBH, by means of a simple analytical model and of hydrodynamical simulations. Through such calculation, we obtain a lower limit to the mass of CO-0.40-0.22* of few $10^4 \times \; M_{\odot}$. This result tends to exclude the formation of such massive black hole in the proximity of the Galactic Centre. On the other hand, CO-0.40-0.22* might have been brought to such distances in cosmological timescales, if it was born in a dark matter halo or globular cluster around the Milky Way.Comment: 9 pages, 4 figures. To be published on MNRA

Forming circumnuclear disks and rings in galactic nuclei: a competition between supermassive black hole and nuclear star cluster

We investigate the formation of circumnuclear gas structures from the tidal disruption of molecular clouds in galactic nuclei, by means of smoothed particle hydrodynamics simulations. We model galactic nuclei as composed of a supermassive black hole (SMBH) and a nuclear star cluster (NSC) and consider different mass ratios between the two components. We find that the relative masses of the SMBH and the NSC have a deep impact on the morphology of the circumnuclear gas. Extended disks form only inside the sphere of influence of the SMBH. In contrast, compact rings naturally form outside the SMBH's sphere of influence, where the gravity is dominated by the NSC. This result is in agreement with the properties of the Milky Way's circumnuclear ring, which orbits outside the SMBH sphere of influence. Our results indicate that compact circumnuclear rings can naturally form outside the SMBH sphere of influence.Comment: Accepted for publication in ApJ. 12 pages, 6 figures, 3 tables. Comments welcom

Els efectes del context fonètic en el procés d'asil·labació de l'article lo/los en català

El català de l'Alguer conserva els articles definits masculins lo/los. Segons la bibliografia disponible, aquestos articles perden com a regla general la vocal nuclear quan són precedits de paraula que comença amb vocal, però no són disponibles estudis empírics de tipus quantitatiu a aquest propòsit. El nostre treball té com a objectiu principal investigar, a través d'una anàlisi impressionista sobre un corpus alguerès de parla espontània i semiespontània, quins contextos fonètics poden facilitar el procés d'asil·labació de lo/los. Els nostres resultats indiquen que la presència d'una vocal que precedeix l'article és una condició necessària però no suficient per a activar l'asil·labació. A més d'això, el procés en qüestió s'activa de manera quantitativament minoritària (ca. 1 ocurrència de cada 3) en el context V+article definit masculí, fet aquest no previst per la bibliografia disponible. També s'han trobat indicis de contextos fonètics immediatament successius que poden bloquejar l'asil·labació de l'article.Algherese Catalan preserves the masculine definite articles lo/los. According to the available literature, these determiners generally lose their vowel when they are immediately preceded by a word ending in a vowel. However, there are no empirical studies with quantitative data available on the subject. The main goal of our paper is to investigate, by means of an auditory impressionistic analysis of spontaneous and semi-spontaneous Algherese speech, which phonetic contexts trigger resyllabification of lo/los with deletion of the vowel. Our results show that the presence of a vowel preceding these articles is a necessary but not a sufficient condition to trigger vowel loss. Furthermore, contrary to the available literature, vowel loss in the context V+lo/los cannot be considered a general rule, since it only affects one article out of three. Our results indicate that there are specific phonetic contexts immediately following the articles that can block vowel loss

Els efectes del context fonètic en el procés d'asil·labació de l'article lo/los en català

El català de l'Alguer conserva els articles definits masculins lo/los. Segons la bibliografia disponible, aquestos articles perden —com a regla general— la vocal nuclear quan són precedits de paraula que comença amb vocal, però no són disponibles estudis empírics de tipus quantitatiu a aquest propòsit. El nostre treball té com a objectiu principal investigar, a través d'una anàlisi impressionista sobre un corpus alguerès de parla espontània i semiespontània, quins contextos fonètics poden facilitar el procés d'asil·labació de lo/los. Els nostres resultats indiquen que la presència d'una vocal que precedeix l'article és una condició necessària però no suficient per a activar l'asil·labació. A més d'això, el procés en qüestió s'activa de manera quantitativament minoritària (ca. 1 ocurrència de cada 3) en el context V+article definit masculí, fet aquest no previst per la bibliografia disponible. També s'han trobat indicis de contextos fonètics immediatament successius que poden bloquejar l'asil·labació de l'article.Algherese Catalan preserves the masculine definite articles lo/los. According to the available literature, these determiners generally lose their vowel when they are immediately preceded by a word ending in a vowel. However, there are no empirical studies with quantitative data available on the subject. The main goal of our paper is to investigate, by means of an auditory impressionistic analysis of spontaneous and semi-spontaneous Algherese speech, which phonetic contexts trigger resyllabification of lo/los with deletion of the vowel. Our results show that the presence of a vowel preceding these articles is a necessary but not a sufficient condition to trigger vowel loss. Furthermore, contrary to the available literature, vowel loss in the context V+lo/los cannot be considered a general rule, since it only affects one article out of three. Our results indicate that there are specific phonetic contexts immediately following the articles that can block vowel loss

Early die out events in SIR epidemic models

We are interested in the behavior of an SIR epidemic model with respect to low-probability events. Specifically, we want to identify the probability of the early die out of a disease. Ordinary differential equations are commonly used to model SIR systems. However, this approach fails to describe the spontaneous die out event. We develop a Markov SIR model from which the probability of early die out can be captured. Additional simulations reveal that this model agrees closely with the ODE solutions when these low-probability events are ignored

Sobre la correcta interpretació dels fonemes vocàlics de l’alguerès: un estudi acústic

Resum: En els treballs de dialectologia catalana són sovent presents errors en la interpretació dels fonemes vocàlics del català de l’Alguer, i especialment dels fonemes mitjans /e, ?, ?, o/. L’objectiu principal d’aquest estudi és d’avaluar instrumentalment el rol que la distribució al·lofònica de les vocals tòniques en l’espai vocàlic pot jugar en augmentar el risc de no interpretar correctament els fonemes algueresos per part de locutors d’altres àrees dialectals del domini lingüístic català.Les dades obtingudes indiquen que és suposable una correlació entre diferències acústiquesdialectals i errades interpretacions dels fonemes vocàlics de l’alguerès per part d’estudiosos catalanoparlants no algueresos. Per exemple, una certa tendència a interpretar les vocals mitjanes obertes de l’alguerès com a mitjanes tancades pot ésser atribuïda (entre d’altres possibles factors) a la llur realització perceptiblement més alta respecte a les corresponents en quasi totes les altres varietats considerades.Paraules clau: alguerès, català, vocals, fonètica segmental, fonologia, escala Bark.Abstract: Research on the Catalan dialects, often include mistakes in the interpretation of the Algherese vowel phonemes, and especially of the mid vowels /e, ?, ?, o/. The main goal of this study is to instrumentally evaluate the role played by the allophonic distribution of stressed vowels in the vowel space in increasing the risk of the misinterpretation of Algherese vowels by other Catalan speakers.As a result, the data obtained suggest a correlation between dialectal acoustic differences and the incorrect interpretation of Algherese vowel phonemes by non-Algherese scholars. For example, a tendency to interpret open-mid Algherese vowels as close-mid can be attributed (among otherfactors) to their realisation as perceptively higher than the corresponding ones in almost all the other varieties analysed in this study.Key words: Algherese, Catalan, vowels, segmental phonetics, phonology, Bark scale

Mesophases in Nearly 2D Room-Temperature Ionic Liquids

Computer simulations of (i) a [C12mim][Tf2N] film of nanometric thickness squeezed at kbar pressure by a piecewise parabolic confining potential reveal a mesoscopic in-plane density and composition modulation reminiscent of mesophases seen in 3D samples of the same room-temperature ionic liquid (RTIL). Near 2D confinement, enforced by a high normal load, relatively long aliphatic chains are strictly required for the mesophase formation, as confirmed by computations for two related systems made of (ii) the same [C12mim][Tf2N] adsorbed at a neutral solid surface and (iii) a shorter-chain RTIL ([C4mim][Tf2N]) trapped in the potential well of part i. No in-plane modulation is seen for ii and iii. In case ii, the optimal arrangement of charge and neutral tails is achieved by layering parallel to the surface, while, in case iii, weaker dispersion and packing interactions are unable to bring aliphatic tails together into mesoscopic islands, against overwhelming entropy and Coulomb forces. The onset of in-plane mesophases could greatly affect the properties of long-chain RTILs used as lubricants.Comment: 24 pages 10 figure