23 research outputs found
Peierls Instabilities in Quasi-One-Dimensional Quantum Double-Well Chains
Peierls-type instabilities in quarter-filled () and half-filled
() quantum double-well hydrogen-bonded chain are investigated
analytically in the framework of two-stage orientational-tunnelling model with
additional inclusion of the interactions of protons with two different optical
phonon branches. It is shown that when the energy of proton-phonon coupling
becomes large, the system undergoes a transition to a various types of
insulator states. The influence of two different transport amplitudes on ground
states properties is studied. The results are compared with the pressure effect
experimental investigations in superprotonic systems and hydrogen halides at
low temperatures.Comment: 7 pages, RevTeX, 9 eps figure
Dipolar-controlled spin tunneling and relaxation in molecular magnets
Spin tunneling in molecular magnets controlled by dipole-dipole interactions
(DDI) in the disordered state has been considered numerically on the basis of
the microscopic model using the quantum mean-field approximation. In the actual
case of a strong DDI spin coherence is completely lost and there is a slow
relaxation of magnetization, described by t^{3/4} at short times. Fast
precessing nuclear spins, included in the model microscopically, only
moderately speed up the relaxation.Comment: 10 pages, 9 figures, to be published in EPJ
Thermodynamic properties and structural features of water at normal and high pressures
International audienc
Thermodynamic properties and structural features of water at normal and high pressures
International audienc
The Campanian Ignimbrite and Codola tephra layers: two temporal/stratigraphic markers for the Early Upper Palaeolithic in southern Italy and eastern Europe
Tephra layers from archaeological sites in southern Italy and eastern Europe stratigraphically associated with
cultural levels containing Early Upper Palaeolithic industry were analysed. The results confirm the
occurrence of the Campanian Ignimbrite tephra (CI; ca. 40 cal ka BP) at Castelcivita Cave (southern Italy),
Temnata Cave (Bulgaria) and in the KostenkiâBorshchevo area of the Russian Plain. This tephra, originated
from the largest eruption of the Phlegrean Field caldera, represents the widest volcanic deposit and one of
the most important temporal/stratigraphic markers of western Eurasia. At Paglicci Cave and lesser sites in the
Apulia region we recognise a chemically and texturally different tephra, which lithologically, chronologically
and chemically matches the physical and chemical characteristics of the Plinian eruption of Codola; a poorly
known Late Pleistocene explosive event from the Neapolitan volcanoes, likely SommaâVesuvius. For this
latter, we propose a preliminary age estimate of ca. 33 cal ka BP and a correlation to the widespread C-10
marine tephra of the central Mediterranean. The stratigraphic position of both CI and Codola tephra layers at
Castelcivita and Paglicci help date the first and the last documented appearance of Early Upper Palaeolithic
industries of southern Italy to ca. 41â40 and 33 cal ka BP, respectively, or between two interstadial
oscillations of the Monticchio pollen record â to which the CI and Codola tephras are physically correlated â
corresponding to the Greenland interstadials 10â9 and 5. In eastern Europe, the stratigraphic and
chronometric data seem to indicate an earlier appearance of the Early Upper Palaeolithic industries, which
would predate of two millennia at least the overlying CI tephra. The tephrostratigraphic correlation indicates
that in both regions the innovations connected with the so-called Early Upper Palaeolithic â encompassing
subsistence strategy and stone tool technology â appeared and evolved during one of the most unstable
climatic phases of the Last Glacial period. On this basis, the marked environmental unpredictability
characterising this time-span is seen as a potential ecological factor involved in the cultural changes
observed