91 research outputs found
La "realtà" secondo la Meccanica Quantistica: dalla funzione d'onda all'entanglement.
No full textQuantum Mechanics is the very successful theory on which our understanding of the “microscopic” world is based. However, the weltanschauung put forward by Quantum Mechanics clashes with the familiar rules of the “macroscopic” world in which we customarily live in. In this essay, after briefl y recapping the history of the origin of Quantum Mechanics, I will describe the three major points of departure between the classical and quantum-mechanical description of the world, namely the superposition principle, the complementarity principle and the phenomenon of entanglement. Th ese concepts are introduced by a constant comparison between ideal and actual experiments
Zeolitic imidazolate frameworks for separation of binary mixtures of CO2, CH4,N2 and H2 : A computer simulation investigation
No full textCollective properties of water confined in carbon nanotubes: a computer simulation study.
No full textThe collective properties of water confined in the (10,10), (8,8) and (6,6) carbon nanotubes are studied by analysing the longitudinal-current autocorrelation function, calculated from computer-simulated trajectories. The corresponding spectra clearly show the presence of two excitations, but their behaviour is quite different from that observed in the case of bulk water. Instead of the strong positive dispersion of the hydrodynamic sound mode characteristic of bulk water (the fast-sound phenomenon), the sound dispersion relation of confined water is observed to flatten into a non-propagating mode, while a second excitation appears at a higher frequency. This behaviour is analysed in terms of the localized oscillation modes of the hydrogen-bond network
Quantum states of rigid linear rotors confined in a slit pore: quantum sieving of hydrogen isotopes and extreme one dimensional confinement
No full textThe quantum states of molecular hydrogen isotopes confined in carbon slit
pores of varying width are calculated by direct diagonalization of the single
particle Hamiltonian, evaluated with a model potential.
The results are used to calculate the zero-pressure isotopic selectivity that
can be expected from adsorption on these nanostructures, and the contribution
from the rotational degrees of freedom is analysed in detail. It is shown
that the role of the rotational degrees of freedom is far from negligible,
resulting in values of the isotopic separation 8 to 50 times higher
than those calculated using spherically symmetric models for the hydrogen
molecule.
It is also shown that if the pores are narrow enough, the molecular axis in
the ground state is found preferentially aligned along the slit planes, and
the conditions when this happens will be analysed in detail. This behaviour,
termed “extreme one dimensional confinement”, is analogous to a similar
behaviour observed in carbon nanotubes
Instantaneous normal mode analysis of correlated cluster motions in hydrogen bonded liquids
No full textWe analyze the correlated motions of hydrogen bonded clusters in liquid hydrogen fluoride, methanol, and water using the Instantaneous Normal Mode approach. In the case of hydrogen fluoride and methanol, which form a topologically linear hydrogen bond network, the relevant cluster is a triplet formed by a molecule and its two neighbors. In the case of water, whose hydrogen bond structure has a local tetrahedral symmetry, the basic unit considered is the pentamer formed by a molecule and its four neighbors. For each of these clusters we identify, using symmetry arguments, the a priori modes describing the relative motions of the cluster molecules and introduce suitable projections in order to evaluate how much these modes contribute to the actual motions at different frequencies. In the case of hydrogen fluoride we confirm the assignment of a 50 rad/ps peak observed in the single and collective correlation function spectra to the stretching of the hydrogen bonded network. In the case of methanol the analysis of the correlated motions of the triplets shows that in the intermediate frequency range (around 25 rad/ps) a picture similar to what is observed in hydrogen fluoride applies, whereas the high frequency properties of the liquid (beyond 50 rad/ps) are mostly due to the asymmetric stretching motion. In the case of water we demonstrate that the a priori modes, based on the full tetrahedral symmetry of the water pentamer, do indeed mix strongly under the effect of the interaction with the neighbors. The results are related to the spectroscopic measurement. (C) 2002 American Institute of Physics
Finite-range effects in dilute Fermi gases at unitarity
No full textWe develop a theoretical method going beyond the contact-interaction approximation frequently used in mean-field theories of many-fermion systems, based on the low-energy T matrix of the pair potential to rigorously define the effective radius of the interaction. One of the main consequences of our approach is the possibility to investigate finite-density effects, which are outside the range of validity of approximations based on δ-like potentials. We apply our method to the calculation of density-dependent properties of an ultracold gas of 6Li atoms at unitarity, whose two-body interaction potential is calculated using ab initio quantum chemistry methods. We find that density effects will be significant in ultracold gases with densities 1 order of magnitude higher than those attained in current experiments
Microscopic structure of phospholipid bilayers: comparison between molecular dynamics simulations and wide angle X-ray spectra
No full textWe present results of molecular dynamics simulations of fully hydrated dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine bilayers in the disordered liquid crystalline phase (Lalpha) and compare them to wide-angle X-ray scattering experiments. Though we find a generally good agreement between the simulated and experimental spectra, there are some deviations whose origin has been investigated by a reparametrization of the aliphatic chains' force field. A detailed analysis of the various contribution to the X-ray spectra shows that a non-negligible contribution to the total scattered intensity comes from the headgroups and the head-tail cross correlation
Dynamical properties of hydrogen bonded liquids
No full textWe present computer simulation results for the spectra of collective quantities of hydrogen bonded systems which present a different degree of hydrogen bond strength. The present analysis allows to clarify which are the features connected with the presence of a structural arrangement of molecules induced by the hydrogen bonding. Localized motion, is found to be reflected in the appearance of extra peaks in the spectra besides the one related to the acoustic like propagation of density fluctuations. The nature of these modes is discussed taking into account recent investigations performed through ail instantaneous normal mode analysis. For very weakly hydrogen bonded systems (e.g. hydrogen chloride) the spectral behaviour is found to be much more similar to that of simple monatomic liquids
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