Classical and quantum harmonic mean-field models coupled intensively and extensively with external baths

We study the nonequilibrium steady-state of a fully-coupled network of N quantum harmonic oscillators, interacting with two thermal reservoirs. Given the long-range nature of the couplings, we consider two setups: one in which the number of particles coupled to the baths is fixed (intensive coupling) and one in which it is proportional to the size N (extensive coupling). In both cases, we compute analytically the heat fluxes and the kinetic temperature distributions using the nonequilibrium Green's function approach, both in the classical and quantum regimes. In the large N limit, we derive the asymptotic expressions of both quantities as a function of N and the temperature difference between the baths. We discuss a peculiar feature of the model, namely that the bulk temperature vanishes in the thermodynamic limit, due to a decoupling of the dynamics of the inner part of the system from the baths. At variance with the usual case, this implies that the steady-state depends on the initial state of the bulk particles. We also show that quantum effects are relevant only below a characteristic temperature that vanishes as 1/N. In the quantum low-temperature regime the energy flux is proportional to the universal quantum of thermal conductance

Non-equilibrium steady states of long-range coupled harmonic chains

We perform a numerical study of transport properties of a one-dimensional chain with couplings decaying as an inverse power $r^{-(1+\sigma)}$ of the intersite distance $r$ and open boundary conditions, interacting with two heat reservoirs. Despite its simplicity, the model displays highly nontrivial features in the strong long-range regime, $-1<\sigma<0$. At weak coupling with the reservoirs, the energy flux departs from the predictions of perturbative theory and displays anomalous superdiffusive scaling of the heat current with the chain size. We trace back this behavior to the transmission spectrum of the chain, which displays a self-similar structure with a characteristic sigma-dependent fractal dimension.Comment: 9 pages, 8 figure

Evolution and architecture of a West Mediterranean Upper Pleistocene to Holocene coastal apron-fan system

The Quaternary deposits of tectonically stable areas are a powerful tool to investigate high-frequency climate variations (<10 ka) and to distinguish allogenic and autogenic factors controlling deposition. Therefore, an Upper Pleistocene—Holocene coastal apron-fan system in north—western Sardinia (Porto Palmas, Italy) was studied to investigate the relations between climate changes, sea-level fluctuations and sediment source-supply that controlled its development. The sedimentary sequence records the strong influence of local (wet/dry) and worldwide (sea-level) environmental variations in the sedimentation and preservation of the deposits. A multi-disciplinary approach allowed subdivision of the succession into four major, unconformity-bounded stratigraphic units: U1 U2, U3 and U4. Unit U1, tentatively dated to the warm and humid Marine Isotopic Stage (MIS) 5, consists of sandy, gravelly coastal/beach deposits developed during high sea-level in low-lying areas. Unit U2 consists of debris-flow dominated fan-deposits (ca 74 ka; MIS 4), preserved as partial fills of small valleys and coves. Unit U2 is mainly composed of reddish silty conglomerate to pebbly siltstones sourced from the Palaeozoic metamorphic inland hills (bedrock), superficially disintegrated during the preceding warm, vegetation-rich MIS 5. The cold and semi-arid climate strongly reduced vegetation cover along the valley flanks. Therefore, sediment gravity-flow processes, possibly activated by rainstorms, led to deposition of debris-flow dominated fans. Unit U3 consists of water-flow dominated alluvial-fan deposits (ca 47 to 23 ka; MIS 3), developed on a slightly inclined coastal plain. Unit U3 is composed of sandstone and sandy conglomerate fed from two main sediment sources: metamorphic inland bedrock and Quaternary bioclastic-rich shelf-derived sands. During this cold phase, sea-level dropped sufficiently to expose bioclastic sands accumulated on the shelf. Frequent climate fluctuations favoured inland aeolian transport of sand during dry phases, followed by reworking of the aeolian bodies by flash floods during wet phases. Bedrock-derived fragments mixed with water-reworked, wind-blown sands led to the development of water-flow dominated fans. The Dansgaard—Oeschger events possibly associated with sand landward deflation and main fan formations are Dansgaard—Oeschger 13 (ca 47 ka), Dansgaard—Oeschger 8 (ca 39 ka) and Dansgaard—Oeschger 2 (ca 23 ka). No record of sedimentation during MIS 2 was observed. Finally, bioclastic-rich aeolianites (Unit U4, ca 10 to 5 ka; MIS 1), preserved on a coastal slope, were developed during the Holocene transgression (ca 10 to 5 ka; MIS 1). The studied sequence shows strong similarities with those of other Mediterranean sites; it is, however, one of the few where the main MIS 4 and MIS 3 climatic fluctuations are registered in the sedimentary record

Paleoenvironmental implications through the study of an Eemian paleosol in northwestern Sardinia (Italy)

The aim of this work is to define the paleoenvironmental changes related to a soil belonging to the studied succession, by means of an in-depth micromorphological study. In particular, the presence of this paleosol is associated to the fast climatic fluctuations that took place between MIS5e and MIS5c

Stratigraphy and chronology of the Cala Mosca site, SW Sardinia (Italy)

The relict beach deposit of the Cala Mosca marine terrace is considered an important section of Marine Isotopic Stage (MIS) 5e (ca. 125 ka) sea-level highstands. Analysis of the stratigraphy and sediments of the deposit indicates the presence of a composite marine terrace comprising two superimposed marine units, luminescence dated to the MIS 5e (137 ± 7, 134 ± 7 ka) and MIS 5c (92 ± 6 ka) substages. The stratigraphic superimposition of the two highstands, both placed ∼5 m above present sea level, agrees with other areas along the Sardinia coasts. The evident superimposition of two sea-level highstands and development of the composite terrace cannot be accounted solely by high-frequency sea-level oscillation that occurred within MIS 5 for the Mediterranean Sea. This suggests controversial, but significant, regional versus local tectonic activity occurred during the Late Pleistocen

Evolution and architecture of a West Mediterranean upper Pleistocene to Holocene coastal apron-fan system

The Quaternary deposits of tectonically stable areas are a powerful tool to investigate high-frequency climate variations (&#60;10 ka) and to distinguish allogenic and autogenic factors controlling deposition. Therefore, an Upper Pleistocene&#8212;Holocene coastal apron-fan system in north&#8212;western Sardinia (Porto Palmas, Italy) was studied to investigate the relations between climate changes, sea-level fluctuations and sediment source-supply that controlled its development. The sedimentary sequence records the strong influence of local (wet/dry) and worldwide (sea-level) environmental variations in the sedimentation and preservation of the deposits. A multi-disciplinary approach allowed subdivision of the succession into four major, unconformity-bounded stratigraphic units: U1 U2, U3 and U4. Unit U1, tentatively dated to the warm and humid Marine Isotopic Stage (MIS) 5, consists of sandy, gravelly coastal/beach deposits developed during high sea-level in low-lying areas. Unit U2 consists of debris-flow dominated fan-deposits (ca 74 ka; MIS 4), preserved as partial fills of small valleys and coves. Unit U2 is mainly composed of reddish silty conglomerate to pebbly siltstones sourced from the Palaeozoic metamorphic inland hills (bedrock), superficially disintegrated during the preceding warm, vegetation-rich MIS 5. The cold and semi-arid climate strongly reduced vegetation cover along the valley flanks. Therefore, sediment gravity-flow processes, possibly activated by rainstorms, led to deposition of debris-flow dominated fans. Unit U3 consists of water-flow dominated alluvial-fan deposits (ca 47 to 23 ka; MIS 3), developed on a slightly inclined coastal plain. Unit U3 is composed of sandstone and sandy conglomerate fed from two main sediment sources: metamorphic inland bedrock and Quaternary bioclastic-rich shelf-derived sands. During this cold phase, sea-level dropped sufficiently to expose bioclastic sands accumulated on the shelf. Frequent climate fluctuations favoured inland aeolian transport of sand during dry phases, followed by reworking of the aeolian bodies by flash floods during wet phases. Bedrock-derived fragments mixed with water-reworked, wind-blown sands led to the development of water-flow dominated fans. The Dansgaard&#8212;Oeschger events possibly associated with sand landward deflation and main fan formations are Dansgaard&#8212;Oeschger 13 (ca 47 ka), Dansgaard&#8212;Oeschger 8 (ca 39 ka) and Dansgaard&#8212;Oeschger 2 (ca 23 ka). No record of sedimentation during MIS 2 was observed. Finally, bioclastic-rich aeolianites (Unit U4, ca 10 to 5 ka; MIS 1), preserved on a coastal slope, were developed during the Holocene transgression (ca 10 to 5 ka; MIS 1). The studied sequence shows strong similarities with those of other Mediterranean sites; it is, however, one of the few where the main MIS 4 and MIS 3 climatic fluctuations are registered in the sedimentary record

Caratterizzazione fisiografica, geomorfologica e bionomica della <i>Rias</i> di Santa Teresa di Gallura: Sardegna nord-orientale = Physiographic, geomorphological and bionomic characterization of the Santa Teresa di Gallura <i>Rias</i> (N.E. Sardinia)

An underwater survey in the Rias of S. Teresa di Gallura was made to characterize the benthic environment by integrating three methods: Side Scan Sonar, ROV, SCUBA diving. The main bionomic features at different depths were described and mapped. The presence of Savalia savaglia, a rare Mediterranean species contributed to enhance the environmental value of the study area

Climatic changes and human impact on coastal areas of Sardinia: the example of the Mistras-Cabras barrier-lagoon system (Central-Western Sardinia)

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Indagini preliminari su ripartizione e morfologia della prateria a <i>Posidonia oceanica</i> nella rada di Alghero = Preliminary investigations on distribution and morphology of a <i>Posidonia oceanica</i> meadow in the bay of Alghero

An extensive side scan sonar survey has been conducted in the gulf of Alghero (N Sardinia, Italy) in order to map the main morphological and habitat features of the seafloor. The local Posidonia oceanica meadow covers a total area of 13 km2, extending from 2.5 to 35 meters depth and is medially divided by an ancient river channel developed during the last glacial stage