531 research outputs found
Alluvial gravel sedimentation in a contractional growth fold setting, Sant Llorenc de Morunys, southeastern Pyrenees
This paper is included in the Special Publication entitled 'Cenozoic foreland basins of Western Europe' edited by A. Mascle, C. Puigdefabregas, H.P. Luterbacher and M. Fernandez. New data are presented on the classic growth structure at Sant Llorenc de Morunys (NE Ebro Basin, Spain). During the late Eocene to Oligocene thick alluvial-fan gravel sediments accumulated principally by repetitive sub-aerial mass flow (cohesionless debris flow and fluidal sediment flow) events, with smaller volumes of fan-stream flows. Subaerial, high-viscosity (cohesive) debris flows contributed comparatively small volumes of sediment to the succession. These sediments constructed a complex architecture of conglomeratic and sandstone-bearing lithosomes that were affected by stratal thickening and erosion across a growth fold pair and genetically related internal unconformities, which formed a long-lived thrust-related structure in the immediate footwall of the SE Pyrenean mountain front. Four periods of evolution for the Sant Llorenc growth structure are defined on the basis of distintive stratigraphical architecture. These describe a gross evolution from onlapping to overlapping growth strata, related to the ultimate demise of growth folding. In detail complex erosional and offlapping events punctuated the growth history, which shows extreme variation parallel to the axis of the structure. Patterns of palaeoflow were highly complex, showing distinct axial and transverse directions relatable to growth fold evolutionary periods. Palaeocurrents are considered to have been deflected and diverted by surficial differential subsidence and areas of relative uplift and erosion generated by fold growth. The complexity of sediment dispersal is compounded by variables intrinsic to alluvial fan environments. The Sant Llorenc de Morunys growth strata provide information on how sediments are reorganized by syndepositionally-growing structures and on the nature of sediment distribution between external fold-and-thrust belts and foreland basins
Structural Disorder Induced Polaron Formation and Magnetic Scattering in the Disordered Holstein-Double Exchange Model
In this paper we present results on the disordered Holstein-Double Exchange
model, explicitly in three dimension and `metallic' densities, obtained by
using a recently developed Monte Carlo approach. Following up on our earlier
paper, cond-mat/0406085, here we provide a detailed microscopic picture of the
thermally driven metal-insulator transition (MIT) that arises close to the
ferromagnet to paramagnet transition in this problem. This paper is focused
mainly on the `diagnostics', clarifying the origin of the effective disorder
that drives the MIT in this system. To that effect, we provide results on the
thermal evolution of the distributions of (i) lattice distortions, (ii) the net
`structural disorder' and (iii) the `hopping disorder' arising from spin
randomness feeding back through the Hunds coupling. We suggest a phenomenology
for the thermally driven MIT, viewing it as an `Anderson-Holstein' transition.Comment: 6 pages, latex, JPSJ style, 7 eps figs. Style files included.
Proceedings of the SPQS Meeting at Sendai, Japan, 2004. To appear in JPS
Identification of animal species housed and herding practices in ancient sediments from the Vallone Inferno rock-shelter (Scillato, Sicily, Italy) using faecal biomarkers, hormones, and their metabolites
The interest in the identification of animal species housed in caves or rock-shelters used as livestock pen and herding management along prehistoric and historic ages, is increasing to understand better the development of pastoral activities. In this manuscript, a method for the quantification of β-sterol/phytosterols, bile acids, hormones and hormones metabolites has been developed to determine the main pastoral activities carried out in Vallone Inferno rock-shelter (Scillato, Sicily, Italy) from Middle Neolithic to Early Middle Age. According to the result obtained, the main animals housed in the rock-shelter went gradually changing from ovicaprids in Middle Neolithic to pigs in Early Middle Age. Additionally, new proxies (progesterone/Ʃbile acids and metabolites of progesterone/Ʃbile acids) were used to detect a high hormonal activity at Early Middle Age samples related with female pig management
Implications of Charge Ordering for Single-Particle Properties of High-Tc Superconductors
The consequences of disordered charge stripes and antiphase spin domains for
the properties of the high-temperature superconductors are studied. We focus on
angle-resolved photoemission spectroscopy and optical conductivity, and show
that the many unusual features of the experimentally observed spectra can be
understood naturally in this way. This interpretation of the data, when
combined with evidence from neutron scattering and NMR, suggests that
disordered and fluctuating stripe phases are a common feature of
high-temperature superconductors.Comment: 4 pages, figures by fax or mai
Superconductivity of a Metallic Stripe Embedded in an Antiferromagnet
We study a simple model for the metallic stripes found in
: two chain Hubbard ladder embedded in a static
antiferromagnetic environments. We consider two cases: a ``topological
stripe'', for which the phase of the Neel order parameter shifts by
across the ladder, and a ``non-topological stripe'', for which there is no
phase shift across the ladder. We perform one-loop renormalization group
calculations to determine the low energy properties. We compare the results
with those of the isolated ladder and show that for small doping
superconductivity is enhanced in the topological stripe, and suppressed in the
non-topological one. In the topological stripe, the superconducting order
parameter is a mixture of a spin singlet component with zero momentum and a
spin triplet component with momentum . We argue that this mixture is
generic, and is due to the presence of a new term in the quantum
Ginzburg-Landau action. Some consequences of this mixing are discussed.Comment: 6 pages, 3 eps figure
Zinc oxide as an ozone sensor
Journal of Applied Physics, Vol. 96, nº3This work presents a study of intrinsic zinc oxide thin film as ozone sensor based on the ultraviolet sUVd photoreduction and subsequent ozone re oxidation of zinc oxide as a fully reversible process performed at room temperature. The films analyzed were produced by spray pyrolysis, dc and rf
magnetron sputtering. The dc resistivity of the films produced by rf magnetron sputtering and constituted by nanocrystallites changes more than eight orders of magnitude when exposed to an UV dose of 4 mW/cm2. On the other hand, porous and textured zinc oxide films produced by spray pyrolysis at low substrate temperature exhibit an excellent ac impedance response where the reactance changes by more than seven orders of magnitude when exposed to the same UV dose,
with a response frequency above 15 kHz, thus showing improved ozone ac sensing
discrimination
Antiferromagnetism in the Exact Ground State of the Half Filled Hubbard Model on the Complete-Bipartite Graph
As a prototype model of antiferromagnetism, we propose a repulsive Hubbard
Hamiltonian defined on a graph \L={\cal A}\cup{\cal B} with and bonds connecting any element of with all the
elements of . Since all the hopping matrix elements associated with
each bond are equal, the model is invariant under an arbitrary permutation of
the -sites and/or of the -sites. This is the Hubbard model
defined on the so called -complete-bipartite graph,
() being the number of elements in (). In this
paper we analytically find the {\it exact} ground state for at
half filling for any ; the repulsion has a maximum at a critical
-dependent value of the on-site Hubbard . The wave function and the
energy of the unique, singlet ground state assume a particularly elegant form
for N \ra \inf. We also calculate the spin-spin correlation function and show
that the ground state exhibits an antiferromagnetic order for any non-zero
even in the thermodynamic limit. We are aware of no previous explicit analytic
example of an antiferromagnetic ground state in a Hubbard-like model of
itinerant electrons. The kinetic term induces non-trivial correlations among
the particles and an antiparallel spin configuration in the two sublattices
comes to be energetically favoured at zero Temperature. On the other hand, if
the thermodynamic limit is taken and then zero Temperature is approached, a
paramagnetic behavior results. The thermodynamic limit does not commute with
the zero-Temperature limit, and this fact can be made explicit by the analytic
solutions.Comment: 19 pages, 5 figures .ep
Optimal trapping wavelengths of Cs molecules in an optical lattice
The present paper aims at finding optimal parameters for trapping of Cs
molecules in optical lattices, with the perspective of creating a quantum
degenerate gas of ground-state molecules. We have calculated dynamic
polarizabilities of Cs molecules subject to an oscillating electric field,
using accurate potential curves and electronic transition dipole moments. We
show that for some particular wavelengths of the optical lattice, called "magic
wavelengths", the polarizability of the ground-state molecules is equal to the
one of a Feshbach molecule. As the creation of the sample of ground-state
molecules relies on an adiabatic population transfer from weakly-bound
molecules created on a Feshbach resonance, such a coincidence ensures that both
the initial and final states are favorably trapped by the lattice light,
allowing optimized transfer in agreement with the experimental observation
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