Comment on "Collective dynamics in liquid lithium, sodium, and aluminum"

In a recent paper, S. Singh and K. Tankeshwar (ST), [Phys. Rev. E \textbf{67}, 012201 (2003)], proposed a new interpretation of the collective dynamics in liquid metals, and, in particular, of the relaxation mechanisms ruling the density fluctuations propagation. At variance with both the predictions of the current literature and the results of recent Inelastic X-ray Scattering (IXS) experiments, ST associate the quasielastic component of the $S(Q,\omega)$ to the thermal relaxation, as it holds in an ordinary adiabatic hydrodynamics valid for non-conductive liquids and in the $Q \to 0$ limit. We show here that this interpretation leads to a non-physical behaviour of different thermodynamic and transport parameters.Comment: 4 pages, 1 figure, to appear in PRE (scheduled in 1 June issue

Heat capacity of liquids: A hydrodynamic approach

We study autocorrelation functions of energy, heat and entropy densities obtained by molecular dynamics simulations of supercritical Ar and compare them with the predictions of the hydrodynamic theory. It is shown that the predicted by the hydrodynamic theory single-exponential shape of the entropy density autocorrelation functions is perfectly reproduced for small wave numbers by the molecular dynamics simulations and permits the calculation of the wavenumber-dependent specific heat at constant pressure. The estimated wavenumber-dependent specific heats at constant volume and pressure, $C_{v}(k)$ and $C_{p}(k)$, are shown to be in the long-wavelength limit in good agreement with the macroscopic experimental values of $C_{v}$ and $C_{p}$ for the studied thermodynamic points of supercritical Ar.Comment: 8 pages, 5 figure

Acoustic attenuation in glasses and its relation with the boson peak

A theory for the vibrational dynamics in disordered solids [W. Schirmacher, Europhys. Lett. {\bf 73}, 892 (2006)], based on the random spatial variation of the shear modulus, has been applied to determine the wavevector ($k$) dependence of the Brillouin peak position ($\Omega_k)$ and width ($\Gamma_k$), as well as the density of vibrational states ($g(\omega)$), in disordered systems. As a result, we give a firm theoretical ground to the ubiquitous $k^2$ dependence of $\Gamma_k$ observed in glasses. Moreover, we derive a quantitative relation between the excess of the density of states (the boson peak) and $\Gamma_k$, two quantities that were not considered related before. The successful comparison of this relation with the outcome of experiments and numerical simulations gives further support to the theory.Comment: To appear on PR

Benets of tight coupled architectures for the integration of GNSS receiver and Vanet transceiver

Vehicular adhoc networks (VANETs) are one emerging type of networks that will enable a broad range of applications such as public safety, traffic management, traveler information support and entertain ment. Whether wireless access may be asynchronous or synchronous (respectively as in the upcoming IEEE 8021.11p standard or in some alternative emerging solutions), a synchronization among nodes is required. Moreover, the information on position is needed to let vehicular services work and to correctly forward the messages. As a result, timing and positioning are a strong prerequisite of VANETs. Also the diffusion of enhanced GNSS Navigators paves the way to the integration between GNSS receivers and VANET transceiv ers. This position paper presents an analysis on potential benefits coming from a tightcoupling between the two: the dissertation is meant to show to what extent Intelligent Transportation System (ITS) services could benefit from the proposed architectur

Negative electronic compressibility and nanoscale inhomogeneity in ionic-liquid gated two-dimensional superconductors

When the electron density of highly crystalline thin films is tuned by chemical doping or ionic liq- uid gating, interesting effects appear including unconventional superconductivity, sizeable spin-orbit coupling, competition with charge-density waves, and a debated low-temperature metallic state that seems to avoid the superconducting or insulating fate of standard two-dimensional electron systems. Some experiments also find a marked tendency to a negative electronic compressibility. We suggest that this indicates an inclination for electronic phase separation resulting in a nanoscopic inhomo- geneity. Although the mild modulation of the inhomogeneous landscape is compatible with a high electron mobility in the metallic state, this intrinsically inhomogeneous character is highlighted by the peculiar behaviour of the metal-to-superconductor transition. Modelling the system with super- conducting puddles embedded in a metallic matrix, we fit the peculiar resistance vs. temperature curves of systems like TiSe2, MoS2, and ZrNCl. In this framework also the low-temperature debated metallic state finds a natural explanation in terms of the pristine metallic background embedding non-percolating superconducting clusters. An intrinsically inhomogeneous character naturally raises the question of the formation mechanism(s). We propose a mechanism based on the interplay be- tween electrons and the charges of the gating ionic liquid.Comment: substantially modified presentation: 12 pages 7 figure

Sampled 3D models for Cultural Heritage: which uses beyond visualization?

[EN] Digital technologies are now mature for producing high quality digital replicas of Cultural Heritage (CH) artefacts. The research results produced in the last decade have shown an impressive evolution and consolidation of the technologies for acquiring high-quality digital 3D models (3D scanning) and for rendering those models at interactive speed. Technology is now mature enough to push us to go beyond the plain visualization of those assets, devising new tools able to extend our insight and intervention capabilities and to revise the current consolidated procedures for CH research and management. The paper presents a few recent experiences where high-quality 3D models have been used in CH research, restoration and conservation. These examples constitutes a broad review of different uses of digital 3Dassets in the CH domain.[ES] Se puede afirmar que las tecnologías digitales han alcanzado un punto de madurez suficiente como para producir réplicas digitales de alta calidad del patrimonio cultural, especialmente de artefactos. Los resultados de la investigación producidos en la última década han mostrado una impresionante evolución y consolidación de las tecnologías utilizadas para la producción de modelos digitales 3D de alta calidad (escaneado 3D) y para el renderizado de esos modelos a una velocidad interactiva. En este sentido la tecnología es hoy perfectamente capaz de empujarnos a ir más allá de la simple visualización de los bienes culturales, hasta elaborar nuevas herramientas capaces de ampliar nuestra visión y capacidades de intervención así como de revisar los procedimientos actuales de investigación y gestión del patrimonio cultural. Este artículo presenta algunas experiencias recientes en las que modelos 3D de alta calidad han sido utilizados para mejorar la investigación, restauración y conservacióThe research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007- 2013) under grant agreements no. 231809 (IST IP "3DCOFORM") and no. 270404 (IST NoE "V-Must.Net").Scopigno, R. (2012). Sampled 3D models for Cultural Heritage: which uses beyond visualization?. Virtual Archaeology Review. 3(5):109-115. https://doi.org/10.4995/var.2012.4537OJS10911535CALLIERI M., CIGNONI P., GANOVELLI F., IMPOCO G., MONTANI C., PINGI P., PONCHIO F., SCOPIGNO R. (2004): "Visualization and 3D data processing in David's restoration". IEEE Computer Graphics & Applications 24, 2 (Mar.-Apr. 2004), pp. 16-21. http://dx.doi.org/10.1109/MCG.2004.1274056CORSINI M., DELLEPIANE M., DERCKS U., PONCHIO F., CALLIERI M., KEULTJES D., MARINELLO A., SIGISMONDI R., SCOPIGNO R., WOLF G. (2010): "Cenobium - putting together the romanesque cloister capitals of the mediterranean region". In Bar International Series BAR S2118 2010 (Proc. of III International Conference on Remote Sensing in Archaeology, 17th-21st August 2009) (2010), S. Campana M. F., Liuzza C., (Eds.), pp. 189-194.DELLEPIANE M., CALIERI M., DELL'UNTO N. (2011): "Monitoring archeological excavation using dense stereo matching techniques". Tech. rep., CNR-ISTI, Pisa, Italy, 2011.DELLEPIANE M., CALLIERI M., FONDERSMITH M., CIGNONI P., SCOPIGNO R. (2007): "Using 3D scanning to analyze a proposal for the attribution of a bronze horse to Leonardo da Vinci". In The 8th Int. Symp. on International Symposium on Virtual Reality, Archaeology and Cultural Heritage (VAST 07) (Nov 2007), Eurographics, pp. 117-124.DYLLA K., FRISCHER B., MUELLER P., ULMER A., HAEGLER S. (2009): "Rome Reborn 2.0: A case study of virtual city reconstruction using procedural modeling techniques". In 37th Proceedings of the CAA Conference, March 22-26, 2009 (2009), pp. 62-66.HUANG Q.-X., FLORY S., GELFAND N., HOFER M., POTTMANN H. (2006): "Reassembling fractured objects by geometric matching". ACM Trans. Graphics 25, 3 (2006), pp. 569-578. http://dx.doi.org/10.1145/1141911.1141925LEVOY M., PULLI K., CURLESS B., RUSINKIEWICZ S., KOLLER D., PEREIRA L., GINZTON M., ANDERSON S., DAVIS J., GINSBERG J., SHADE J., FULK D. (2000): "The Digital Michelangelo Project: 3D scanning of large statues". In SIGGRAPH 2000, Computer Graphics Proceedings (July 24-28, 2000), Annual Conference Series, AddisonWesley, pp. 131-144. http://dx.doi.org/10.1145/344779.344849SCOPIGNO, Roberto et al. (2011): "Sampled 3D models for CH: beyond plain visualization", IEEE Computer, IEEE Press, July-Aug. 2011, (in press).STANCO F., BATTIATO S., GALLO G., (ed.) (2011): "Digital Imaging for Cultural Heritage Preservation". Taylor & Francis Group, 2011.TOLER-FRANKLIN C., BROWN B., WEYRICH T., FUNKHOUSER T., RUSINKIEWICZ S. (2010): "Multi-feature matching of fresco fragments". ACM Trans. Graphics (Proc. SIGGRAPH Asia) 29, 6 (2010), pp. 185-197. http://dx.doi.org/10.1145/1882262.1866207http://dx.doi.org/10.1145/1882261.186620

Evidence of short time dynamical correlations in simple liquids

We report a molecular dynamics (MD) study of the collective dynamics of a simple monatomic liquid -interacting through a two body potential that mimics that of lithium- across the liquid-glass transition. In the glassy phase we find evidences of a fast relaxation process similar to that recently found in Lennard-Jones glasses. The origin of this process is ascribed to the topological disorder, i.e. to the dephasing of the different momentum $Q$ Fourier components of the actual normal modes of vibration of the disordered structure. More important, we find that the fast relaxation persists in the liquid phase with almost no temperature dependence of its characteristic parameters (strength and relaxation time). We conclude, therefore, that in the liquid phase well above the melting point, at variance with the usual assumption of {\it un-correlated} binary collisions, the short time particles motion is strongly {\it correlated} and can be described via a normal mode expansion of the atomic dynamics.Comment: 7 pages, 7 .eps figs. To appear in Phys. Rev.