30 years of cosmic fullerenes

In 1985, "During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells", Harry Kroto and his collaborators serendipitously discovered a new form of carbon: fullerenes. The most emblematic fullerene (i.e. C$_{60}$ "buckminsterfullerene"), contains exactly 60 carbon atoms organized in a cage-like structure similar to a soccer ball. Since their discovery impacted the field of nanotechnologies, Kroto and colleagues received the Nobel prize in 1996. The cage-like structure, common to all fullerene molecules, gives them unique properties, in particular an extraordinary stability. For this reason and since they were discovered in experiments aimed to reproduce conditions in space, fullerenes were sought after by astronomers for over two decades, and it is only recently that they have been firmly identified by spectroscopy, in evolved stars and in the interstellar medium. This identification offers the opportunity to study the molecular physics of fullerenes in the unique physical conditions provided by space, and to make the link with other large carbonaceous molecules thought to be present in space : polycyclic aromatic hydrocarbons.Comment: To appear in the Proceedings of the annual meeting of the French society of astronomy and astrophysics (SF2A 2015

Relativistic global and local divergences in hydrogenic systems: A study in position and momentum spaces

Relativistic effects in one-particle densities of hydrogenic systems are quantified by means of global and local density functionals: the Jensen-Shannon and the Jensen-Fisher divergences, respectively. The Schrödinger and Dirac radial densities are compared, providing complementary results in position and momentum spaces. While the electron cloud gets compressed towards the origin in the Dirac case, the momentum density spreads out over its domain, and the raising of minima in position space does not occur in the momentum space. Regarding the dependence on the nuclear charge and the state quantum numbers for all divergences here considered, as well as their mutual interconnection, accurate powerlike laws y˜Cxa are found systematically. The parameters {C,a} defining the respective dependences are extremely sensitive to the closeness of the system to the ground and/or the circular state. Particularly interesting are the analyses of (i) the plane subtended by the Jensen-Shannon and Jensen-Fisher divergences, in a given space (position or momentum), and (ii) either of the above two divergences in the position-momentum plane. These kinds of results show the complementary role of global and local divergences and that of both conjugate spaces

A quasi-isodynamic configuration with good confinement of fast ions at low plasma β\beta

A new quasi-isodynamic stellarator configuration optimized for the confinement of energetic ions at low plasma $\beta$ is obtained. The numerical optimization is carried out using the STELLOPT suite of codes. New proxies to measure closeness to quasi-isodynamicity and quality of fast ion confinement have been included. The new configuration has poloidally closed contours of magnetic field strength, low magnetic shear and a rotational transform profile allowing an island divertor. It shows ideal and ballooning magnetohydrodynamic stability up to $\beta = 5$, reduced effective ripple, with $\epsilon_{eff} < 0.5$ in the plasma core. Even at low $\beta$, the configuration approximately satisfies the maximum-$J$ property, and the confinement of fast ions is good at $\beta \sim 1.5$ and becomes excellent at reactor values, $\beta \sim 4$. An evaluation of the $D_{31}$ neoclassical mono-energetic coefficient supports the expectation of a reduced bootstrap current for plasmas confined in quasi-isodynamic configurations. A set of filamentary coils that preserve the good confinement of fast ions in the core is presented.Comment: 21 pages, 16 figure

Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: application to polycyclic aromatic hydrocarbons

The van der Waals dispersion coefficients of a set of polycyclic aromatic hydrocarbons, ranging in size from the single-cycle benzene to circumovalene (C66H20), are calculated with a real-time propagation approach to time-dependent density functional theory (TDDFT). In the non-retarded regime, the Casimir-Polder integral is employed to obtain C6, once the dynamic polarizabilities have been computed at imaginary frequencies with TDDFT. On the other hand, the numerical coefficient that characterizes the fully retarded regime is obtained from the static polarizabilities. This ab initio strategy has favorable scaling with the size of the system - as demonstrated by the size of the reported molecules - and can be easily extended to obtain higher order van der Waals coefficients.Comment: submitted to J. Chem. Phy

All-optical trapping and acceleration of heavy particles

A scheme for fast, compact, and controllable acceleration of heavy particles in vacuum is proposed, in which two counterpropagating lasers with variable frequencies drive a beat-wave structure with variable phase velocity, thus allowing for trapping and acceleration of heavy particles, such as ions or muons. Fine control over the energy distribution and the total charge of the beam is obtained via tuning of the frequency variation. The acceleration scheme is described with a one-dimensional theory, providing the general conditions for trapping and scaling laws for the relevant features of the particle beam. Two-dimensional, electromagnetic particle-in-cell simulations confirm the validity and the robustness of the physical mechanism.Comment: 10 pages, 3 figures, to appear in New Journal of Physic

Dynamics and control of the expansion of finite-size plasmas produced in ultraintense laser-matter interactions

The strong influence of the electron dynamics provides the possibility of controlling the expansion of laser-produced plasmas by appropriately shaping the laser pulse. A simple irradiation scheme is proposed to tailor the explosion of large deuterium clusters, inducing the formation of shock structures, capable of driving nuclear fusion reactions. Such a scenario has been thoroughly investigated, resorting to two- and three-dimensional particle-in-cell simulations. Furthermore, the intricate dynamics of ions and electrons during the collisionless expansion of spherical nanoplasmas has been analyzed in detail using a self-consistent ergodic-kinetic model. This study clarifies the transition from hydrodynamic-like to Coulomb-explosion regimes

Petrological and chronological considerations on the hercynian granitic rocks from Galicia (NW Spain)

[Resumen] Se realiza un estudio sobre más de 600 análisis químicos correspondientes a los diversos grupos de granitoides hercínicos de Galicia, y se establecen valores medios representativos para la composición química mayoritaria de estos grupos. La comparación con las medias previamente establecidas para el N. O. de Galicia, permite observar un desplazamiento hacia términos composicionales más ácidospara el conjunto de los granitoides sincinemáticos más profundos, que resulta notablemente más acentuado en el grupo de los granitoides sincinemáticos predominantemente biotíticos. Para los granitoides postcinemáticos, las desviaciones observadas son en cambio poco significativas. El examen de los datos normativos medios, pone en evidencia un carácter peralumínico generalizado para todo el conjunto, apreciándose no obstante un drástico descenso en el contenido en corindón para los granitoides postcinemáticos, que marca una distribución bimodal para este componente normativo. La clasificación petrológica con base en la mineralogía normativa pone de manifiesto un espectro composicional que fluctúa esencialmente entre granitos y monzogranitos, con muy escasa representación de los términos granodior1ticos. La variabilidad observada para los elementos mayores más signiflcativos presenta pautas poco dispersivas. Los espectros de tierras raras tienen una configuración muy similar para los granitoides precoces predominantemente biotíticos, los granitos de dos micas sincinemáticos y los granitoides inhomogéneos, con anomalías negativas de Eu poco acentuadas. Por el contrario, los granitoides tardicinemáticos someros y los granitoides post-cinemáticos, presentan también espectros bastante similares entre sí, con anomalís negativas de Eu que pueden ser considerables. Las dataciones cronológicas efectuadas por el método de Rb-Sr en roca total en algunos de los plutones post-cinemáticos se encuentran en un intervalo aproximado de 275-287 m. a., mientras que la mayoría de las dataciones sobre unidades sincinemáticas de dos micas y predominantemente biotíticas fluctúan entre 295 y 323 m. a., aunque se encuentran algunos datos fuera de este entorno, que precisan futuras verificaciones..[Abstract] A survey over more than 600 chemical analysis of Hercynian granitic rocks from Galicia is presented, and a new set of representative mean compositional values of the main groups is calculated. In general, these new mean values are richer in Si02 than the previously available ones. This difference is more conspicous in the biotite rich synkinematic group, and is minium in the postkynematic granitoids. The average normative compostion, shows a systematic peraluminous character for aH the granitoids. However, the group of postkynematic granitoids, are poorer in normative corundum than the other groups, which results in a bimodal distribution of this normative component. The normative petrological c1assification shows a compositional spectrúm ranging mainly from granites to monzogranites. The Granodioritic rocks are very scarce. The variation trends for the main mayor elements display patterns with little dispersion. The REE spectra for the biotite rich synkinematic granites, two mica synkinematic granites and inhomogenous granites are very similar, and show negligible Eu anomalies. By contrast, the shaHow level intrusion late-kynematic and postkynematic granites, display conspicous Eu anomalies and have similar spectra patterns, but different from the previously referred ones. Whole-rock-Rb-Sr ages for the postkynematic plutons range from 287 to 275 M. y. The majority of the data the synkinematic units range from 323 to 295 M. y. However, sorne chronological data faH out of these intervals, showing the need of further studies