1,008 research outputs found
Jahn-Teller Spectral Fingerprint in Molecular Photoemission: C60
The h_u hole spectral intensity for C60 -> C60+ molecular photoemission is
calculated at finite temperature by a parameter-free Lanczos diagonalization of
the electron-vibration Hamiltonian, including the full 8 H_g, 6 G_g, and 2 A_g
mode couplings. The computed spectrum at 800 K is in striking agreement with
gas-phase data. The energy separation of the first main shoulder from the main
photoemission peak, 230 meV in C60, is shown to measure directly and rather
generally the strength of the final-state Jahn-Teller coupling.Comment: 5 pages, 3 figure
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
Mechanical properties of carbynes investigated by ab initio total-energy calculations
As sp carbon chains (carbynes) are relatively rigid molecular objects, can we
exploit them as construction elements in nanomechanics? To answer this
question, we investigate their remarkable mechanical properties by ab-initio
total-energy simulations. In particular, we evaluate their linear response to
small longitudinal and bending deformations and their failure limits for
longitudinal compression and elongation.Comment: 6 pages, 4 figures, 1 tabl
Low-energy excitations of a linearly Jahn-Teller coupled orbital quintet
The low-energy spectra of the single-mode h x (G+H) linear Jahn-Teller model
is studied by means of exact diagonalization. Both eigenenergies and
photoemission spectral intensities are computed. These spectra are useful to
understand the vibronic dynamics of icosahedral clusters with partly filled
orbital quintet molecular shells, for example C60 positive ions.Comment: 14 pages revte
Circular Economy: A Performance Evaluation Perspective
Circular Economy has emerged in the last years as an industrial pattern that rethinks the entire design and production cycle of products and goods, to obtain the minimal environmental impact and maximize the energy efficiency. This pattern creates product transformation cycles, that allow to re-use parts and renew energy, defining Circular Economy Ecosystems. Such cycles, are very interesting systems from a performance evaluation point of view: in this paper we give a Colored Petri Net perspective to circular economy. In particular, we focus on an example taken from the literature that considers car manufacturing, and we show how we can deal with the problem using standard performance evaluation techniques. Results from performance analysis of the case study, allow to focus on new interesting metrics and performance indicators, that might not be fully studied with conventional techniques applied by expert of the economical domain
Exactly quantized dynamics of classical incommensurate sliders
We report peculiar velocity quantization phenomena in the classical motion of
an idealized 1D solid lubricant, consisting of a harmonic chain interposed
between two periodic sliders. The ratio v_cm/v_ext of the chain center-of-mass
velocity to the externally imposed relative velocity of the sliders stays
pinned to exact "plateau" values for wide ranges of parameters, such as sliders
corrugation amplitudes, external velocity, chain stiffness and dissipation, and
is strictly determined by the commensurability ratios alone. The phenomenon is
explained by one slider rigidly dragging the kinks that the chain forms with
the other slider. Possible consequences of these results for some real systems
are discussed.Comment: 5 pags 4 fig
Monitoraggio ambientale e biologico dell’esposizione ad idrocarburi mono-aromatici ed a metil tert-butil etere in un gruppo di lavoratori addetti all’erogazione di carburanti
Lo studio è stato condotto per valutare
gli indicatori biologici di esposizione a vapori di benzina
in lavoratori addetti all’erogazione di carburante tramite
un approccio combinato di monitoraggio ambientale
e biologico. L’esposizione personale a benzene, toluene,
etilbenzene e xilene (BTEX) e l’escrezione urinaria di BTEX,
metil tert-butil etere (MTBE-U), degli acidi trans,transmuconico
(t,t-MA) ed S-fenilmercapturico (S-PMA) e della
cotinina sono stati valutati con tecniche cromatografiche
accoppiate alla spettrometria di massa. I livelli di MTBE-U
erano influenzati dalla sola esposizione professionale a vapori
di benzina, mentre quelli di B-U ed S-PMA dipendevano
da abitudine tabagica ed esposizione professionale
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