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Characterization of the noble gases and CRE age of the D'Orbigny angrite
Introduction: The D’Orbigny angrite, a 16.55 kg stone, was found 1979 in Argentina [1]. Mineralogy and chemistry of this meteorite were characterized in detail [2-6]. A Pb-U-Th age of 4.559 Ga was obtained for pyroxenes by Jagoutz et al. [7]. Here we report results on the noble gas isotopic composition and, in particular, on the cosmic-ray exposure (CRE) age of D’Orbigny
Runoff at the micro-plot and slope scale following wildfire, central Portugal
Through their effects on soil properties and vegetation/litter cover, wildfires can strongly enhance overland flow generation and accelerate soil erosion [1] and, thereby, negatively affect land-use sustainability as well as downstream aquatic and flood zones. Wildfires are a common phenomenon in present-day Portugal, devastating in an average year some 100.000 ha of forest and woodlands and in an exceptional year like 2003 over 400.000 ha. There therefore exists a clear need in Portugal for a tool that can provide guidance to post-fire land management by predicting soil erosion risk, on the one hand, and, on the other, the mitigation effectiveness of soil conservation measures. Such a tool has recently been developed for the Western U.S.A. [3: ERMiT] but its suitability for Portuguese forests will need to be corroborated by field observations.
Testing the suitability of existing erosion models in recently burned forest areas in Portugal is, in a nutshell, the aim of the EROSFIRE projects. In the first EROSFIRE project the emphasis was on the prediction of erosion at the scale of individual hill slopes. In the ongoing EROSFIRE-II project the spatial scope is extended to include the catchment scale, so that also the connectivity between hill slopes as well as channel and road processes are being addressed. Besides ERMiT, the principal models under evaluation for slope-scale erosion prediction are: (i) the variant of USLE [4] applied by the Portuguese Water Institute after the wildfires of 2003; (ii) the Morgan–Morgan–Finney model (MMF) [5]; (iii) MEFIDIS [6]. From these models, MEFIDIS and perhaps MMF will, after successful calibration at the slope scale, also be applied for predicting catchment-scale sediment yields of extreme events
Runoff and erosion at the micro-plot and slope scale in a small burnt catchment, central Portugal
Wildfires can have important impacts on hydrological processes and soil erosion in forest catchments, due to the destruction of vegetation cover and changes to soil properties. However, the processes involved are non-linear and not fully understood. This has severely limited the understanding on the impacts of wildfires, especially in the up-scaling from hillslopes to catchments; in consequence, current models are poorly adapted for burnt forest conditions.
The objective of this presentation is to give an overview of the hydrological response and sediment yield from the micro-plot to slope scale, in the first year following a wildfire (2008/2009) that burnt an entire catchment nearby the Colmeal village, central Portugal. The overview will focus on three slopes inside the catchment, with samples including:
• Runoff at micro-plot scale (12 bounded plots) and slope scale (12 open plots); • Sediments and Organic Matter loss at micro-plot scale (12 bounded plots) and slope scale (12 open plots plus 3 Sediment fences); • Rainfall and Soil moisture data; • Soil Water Repellency and Ground Cover data.
The analysis of the first year following the wildfire clearly shows the complexity of runoff generation and the associated sediment transport in recently burnt areas, with pronounced differences between hillslopes and across spatial scales as well as with marked variations through time.
This work was performed in the framework of the EROSFIRE-II project (PTDC/AGR-CFL/70968/2006) which has as overall aim to predict soil erosion risk in recently burnt forest areas, including common post-fire forest management practices; the project focuses on the simultaneous measurement of runoff and soil erosion at multiple spatial scales.The results to be presented in this session are expected to show how sediment is generated, transported and exported in the Colmeal watershed; and contribute to understand and simulate erosion processes in burnt catchments, including for model development and evaluation
Effects of epitaxial strain on the growth mechanism of YBa2Cu3O7-x thin films in [YBa2Cu3O7-x / PrBa2Cu3O7-x] superlattices
We report on the growth mechanism of YBa2Cu3O7-x (YBCO). Our study is based
on the analysis of ultrathin, YBa2Cu3O7-x layers in c-axis oriented YBa2Cu3O7-x
/ PrBa2Cu3O7-x superlattices. We have found that the release of epitaxial
strain in very thin YBCO layers triggers a change in the dimensionality of the
growth mode. Ultrathin, epitaxially strained, YBCO layers with thickness below
3 unit cells grow in a block by block two dimensional mode coherent over large
lateral distances. Meanwhile, when thickness increases, and the strain relaxes,
layer growth turns into three dimensional, resulting in rougher layers and
interfaces.Comment: 10 pages + 9 figures, accepted in Phys. Rev.
Superconductivity and charge carrier localization in ultrathin bilayers
/ (LSCO15/LCO) bilayers
with a precisely controlled thickness of N unit cells (UCs) of the former and M
UCs of the latter ([LSCO15\_N/LCO\_M]) were grown on (001)-oriented {\slao}
(SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and
reciprocal space map (RSM) studies confirmed the epitaxial growth of the
bilayers and showed that a [LSCO15\_2/LCO\_2] bilayer is fully strained,
whereas a [LSCO15\_2/LCO\_7] bilayer is already partially relaxed. The
\textit{in situ} monitoring of the growth with reflection high energy electron
diffraction (RHEED) revealed that the gas environment during deposition has a
surprisingly strong effect on the growth mode and thus on the amount of
disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15
containing one plane each). For samples grown in pure
gas (growth type-B), the first LSCO15 UC next to the SLAO
substrate is strongly disordered. This disorder is strongly reduced if the
growth is performed in a mixture of and gas
(growth type-A). Electric transport measurements confirmed that the first UC of
LSCO15 next to the SLAO substrate is highly resistive and shows no sign of
superconductivity for growth type-B, whereas it is superconducting for growth
type-A. Furthermore, we found, rather surprisingly, that the conductivity of
the LSCO15 UC next to the LCO capping layer strongly depends on the thickness
of the latter. A LCO capping layer with 7~UCs leads to a strong localization of
the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity.
The magneto-transport data suggest a similarity with the case of weakly hole
doped LSCO single crystals that are in a so-called {"{cluster-spin-glass
state}"
Spin polarization induced by decoherence in a tunneling one-dimensional Rashba model
Basic questions on the nature of spin polarization in two terminal systems
and the way in which decoherence breaks Time-Reversal Symmetry (TRS) are
analyzed. We exactly solve several one-dimensional models of tunneling
electrons and show the interplay of spin precession and decay of the
wavefunction in either a U(1) magnetic field or an effective Spin-Orbit (SO)
magnetic field. Spin polarization is clearly identified as the emergence of a
spin component parallel to either magnetic field. We show that Onsager's
reciprocity is fulfilled when time reversal symmetry is present and no spin
polarization arises, no matter the barrier parameters or the SO strength.
Introducing a Buttiker's decoherence probe, that preserves unitarity of time
evolution, we show that breaking of TRS results in a strong spin polarization
for realistic SO, and barrier strengths. We discuss the significance of these
results as a very general scenario for the onset of the Chiral-Induced Spin
Selectivity effect (CISS), now possibly matching experiments in a quantitative
manner.Comment: 24 pages, 14 figure
Surface roughness and thermal conductivity of semiconductor nanowires: going below the Casimir limit
By explicitly considering surface roughness at the atomic level, we
quantitatively show that the thermal conductivity of Si nanowires can be lower
than Casimir's classical limit. However, this violation only occurs for deep
surface degradation. For shallow surface roughness, the Casimir formula is
shown to yield a good approximation to the phonon mean free paths and
conductivity, even for nanowire diameters as thin as 2.22 nm. Our exact
treatment of roughness scattering is in stark contrast with a previously
proposed perturbative approach, which is found to overpredict scattering rates
by an order of magnitude. The obtained results suggest that a complete
theoretical understanding of some previously published experimental results is
still lacking.Comment: 11 pages, 4 figure
Riscos genĂ©ticos da produção de hĂbridos de peixes nativos.
A produção de peixes nativos e seus hĂbridos chama a atenção daqueles que observam o Brasil como alvo de investimentos agropecuários e futura potĂŞncia da aquicultura mundial. Dada a competitividade e dinamismo, o mercado aquĂcola nacional tem motivado a produção de hĂbridos em maior escala nos Ăşltimos anos, buscando neles caracterĂsticas favoráveis de ganho de peso, resistĂŞncia ao frio, rusticidade e adaptação Ă alimentação artificial. Por outro lado, a mistura de animais hĂbridos sobre as linhagens puras e o seu escape inadvertido para os ambientes naturais certamente expõe a sustentabilidade da aquicultura. Sendo assim, este documento buscou reunir informações sobre a produção, impacto genĂ©tico, riscos e desafios do cultivo de hĂbridos frente ao desafio de equilibrar a conservação da biodiversidade com a produção sustentável de alimentos.bitstream/item/131431/1/cnpasadoc3.pd
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