Finite H2 concentrations in superfluid 4He

We have studied the solubility of molecular hydrogen in bulk liquid $^4$He at zero temperature using the diffusion Monte Carlo method and realistic interatomic potentials between the different species of the mixture. Around the $^4$He equilibrium density, the H_2 molecules clusterize in liquid-like drops blocking the existence of a uniform dilution. On the contrary, at higher densities the cluster formation is less feasible and metastable dilute solutions may exist.Comment: 2 pages, 2 eps figures, contribution to the LT22 Conferenc

Isotopic effects of hydrogen adsorption in carbon nanotubes

We present diffusion Monte Carlo calculations of D$_2$ adsorbed inside a narrow carbon nanotube. The 1D D$_2$ equation of state is reported, and the one-dimensional character of the adsorbed D$_2$ is analyzed. The isotopic dependence of the constitutive properties of the quantum fluid are studied by comparing D$_2$ and H$_2$. Quantum effects due to their different masses are observed both in the energetic and the structural properties. The influence of the interatomic potential in one-dimensional systems is also studied by comparing the properties of D$_2$ and $^4$He which have nearly the same mass but a sizeably different potential. The physics of molecular hydrogen adsorbed in the interstitial channels of a bundle of nanotubes is analyzed by means of both a diffusion Monte Carlo calculation and an approximate mean field method.Comment: 17 pages, revtex, 9 ps figures, to be appear in Phys. Rev.

Reseñas

Obra ressenyada: José CHABÁS, Bernard R. GOLDSTEIN, A Survey of European Astronomical. Tables in the Late Middle Ages. [Time, Astronomy and Calendars. Texts and Studies, vol. 2] Brill : Leiden ; Boston, 2012

Mercat a la Rambla del Poblenou

El projecte busca la total adequació al lloc on es posa, trobant una ubicació estratègica del nou edifici en una dinàmica urbana com es la del barri del Poble Nou. El Projecte apunta a ser un executiu, tocant temes urbanístics, “de concepte”, 3D. També arriba a definir aspectes molt més tècnics (electricitat, sanejament, climatització, detalls constructius i estructurals)

Quantum Monte Carlo estimation of complex-time correlations for the study of the ground-state dynamic structure function

We present a method based on the Path Integral Monte Carlo formalism for the calculation of ground-state time correlation functions in quantum systems. The key point of the method is the consideration of time as a complex variable whose phase $\delta$ acts as an adjustable parameter. By using high-order approximations for the quantum propagator, it is possible to obtain Monte Carlo data all the way from purely imaginary time to $\delta$ values near the limit of real time. As a consequence, it is possible to infer accurately the spectral functions using simple inversion algorithms. We test this approach in the calculation of the dynamic structure function $S(q,\omega)$ of two one-dimensional model systems, harmonic and quartic oscillators, for which $S(q,\omega)$ can be exactly calculated. We notice a clear improvement in the calculation of the dynamic response with respect to the common approach based on the inverse Laplace transform of the imaginary-time correlation function.Comment: Accepted for publication on "Jornal of Chemical Physics