2,986 research outputs found
Vacuumless kinks systems from vacuum ones, an example
Some years ago, Cho and Vilenkin, introduced a model which presents
topological solutions, despite not having degenerate vacua as is usually
expected. Here we present a new model with topological defects, connecting
degenerate vacua but which in a certain limit recovers precisely the one
proposed originally by Cho and Vilenkin. In other words, we found a kind of
parent model for the so called vacuumless model. Then the idea is extended to a
model recently introduced by Bazeia et al. Finally, we trace some comments the
case of the Liouville model.Comment: 11 pages, 4 figure
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
Sistemas silvipastoriles agroecológicos con espécies nativas como estratégia de conservassem de la biodiversidad.
IUFROLAT 2013. Disponibilizado online. Resumen
Diagnostic value of oral challenge tests with food additives or nickel sulphate
Objectivo: O uso crescente de aditivos na indústria alimentar e farmacêutica tem dificultado o diagnóstico das reacções adversas a estes produtos. O grande desafio é, actualmente, determinar em cada doente a substância a testar. Constituiu objectivo deste trabalho a avaliação do valor diagnóstico das provas de provocação, utilizando cápsulas de aditivos alimentares ou de nÃquel, em doentes com suspeita, respectivamente, de intolerância alimentar ou de hipersensibilidade ao nÃquel.
Métodos: IncluÃram-se num estudo prospectivo doentes observados consecutivamente, numa consulta de alergia alimentar, num perÃodo de dois anos, com suspeita de intolerância alimentar ou de dermatite sistémica ao nÃquel. Após exclusão de um mecanismo de hipersensibilidade mediado por IgE e revisão dos diários de dieta, os doentes foram submetidos, durante seis semanas, a dieta restritiva em aditivos alimentares ou alimentos com alto teor em nÃquel. Durante o perÃodo de estudo procedeu-se ao registo das reacções adversas e medicamentos consumidos. Nos doentes com lesões de eczema efectuaram-se testes epicutâneos. Os doentes que beneficiaram da dieta restritiva foram submetidos, em regime de internamento, a provas de provocação oral (PPO), controladas por placebo, utilizando cápsulas de aditivos alimentares ou de nÃquel. Os aditivos foram seleccionados de acordo com a história clÃnica.
Resultados: Dos 27 doentes submetidos a dieta restritiva, 19 (17 do sexo feminino) apresentaram melhoria clÃnica, pelo que foram submetidos a PPO. A ocorrência de urticária e/ou angioedema após ingestão de aditivos alimentares foi referida por 15 doentes (seis referiam sintomas também com medicamentos). Em três doentes observaram-se lesões de eczema generalizadas que foram, gradualmente, desaparecendo com a dieta restritiva em nÃquel. Em cinco doentes registaram-se testes epicutâneos positivos (em quatro ao sulfato de nÃquel e dicromato de potássio e numa doente a mistura de fragrâncias, timerosal e resina de butilfenol formaldeÃdo). Das 25 PPO efectuadas, 14 foram positivas (metabissulfito de sódio-5, benzoato de sódio-3, sulfato de nÃquel-3, lactose-1, soja-1, amido de trigo-1). Numa mesma doente obtivemos 2 PPO positivas: ao benzoato de sódio e à lactose. Com a evicção especÃfica dos aditivos ou de alimentos com alto teor em nÃquel, observou-se uma evolução favorável. Conclusões: As PPO permitiram o diagnóstico de dermatite de contacto sistémica, induzida pela ingestão de nÃquel em três doentes e de intolerância alimentar em dez, possibilitando o seguimento de dietas menos restritivas
Non-sequential double ionization below laser-intensity threshold: Anticorrelation of electrons without excitation of parent ion
Two-electron correlated spectra of non-sequential double ionization below
laser-intensity threshold are known to exhibit back-to-back scattering of the
electrons, viz., the anticorrelation of the electrons. Currently, the widely
accepted interpretation of the anticorrelation is recollision-induced
excitation of the ion plus subsequent field ionization of the second electron.
We argue that another mechanism, namely simultaneous electron emission, when
the time of return of the rescattered electron is equal to the time of
liberation of the bounded electron (the ion has no time for excitation), can
also explain the anticorrelation of the electrons in the deep below
laser-intensity threshold regime. Our conclusion is based on the results of the
numerical solution of the time-dependent Schr\"{o}dinger equation for a model
system of two one-dimensional electrons as well as an adiabatic analytic model
that allows for a closed-form solution.Comment: 6 pages and 3 figure
Abundance trend with condensation temperature for stars with different Galactic birth places
During the past decade, several studies reported a correlation between
chemical abundances of stars and condensation temperature (also known as Tc
trend). However, the real astrophysical nature of this correlation is still
debated. The main goal of this work is to explore the possible dependence of
the Tc trend on stellar Galactocentric distances, Rmean. We used high-quality
spectra of about 40 stars observed with the HARPS and UVES spectrographs to
derive precise stellar parameters, chemical abundances, and stellar ages. A
differential line-by-line analysis was applied to achieve the highest possible
precision in the chemical abundances. We confirm previous results that [X/Fe]
abundance ratios depend on stellar age and that for a given age, some elements
also show a dependence on Rmean. When using the whole sample of stars, we
observe a weak hint that the Tc trend depends on Rmean. The observed dependence
is very complex and disappears when only stars with similar ages are
considered. To conclude on the possible dependence of the Tc trend on the
formation place of stars, a larger sample of stars with very similar
atmospheric parameters and stellar ages observed at different Galactocentric
distances is neededComment: Accepted by A&
Nickel induced endogenous dermatitis: two cases report
A sensibilização ao nÃquel representa uma das principais causas de dermatite de contacto alérgica. Um número significativo de doentes apresenta lesões cutâneas, em locais que não estão em contacto directo com este metal. Nos últimos anos a influência do conteúdo em nÃquel da dieta na evolução da dermatite ao nÃquel tem merecido particular atenção.
Descrevem-se os casos de duas doentes com dermatite de contacto ao nÃquel em que, apesar da evicção total do contacto com este metal, persistiam lesões de dermatite eczematosa, predominando nas zonas de maior sudação. Com a exclusão da dieta de alimentos com alto teor em nÃquel observou-se uma redução progressiva da intensidade do eczema, conducente ao desaparecimento total das lesões. As doentes foram, então, submetidas a prova de provocação oral com sulfato de nÃquel. Na primeira doente estudada observou-se aparecimento de eritema, prurido e reacção eczematosa, generalizados, doze horas após a ingestão de 20 mg de sulfato de nÃquel. Concomitantemente verificou-se a ocorrência de eritema pruriginoso e pequenas vesÃculas, no local de aplicação do patch teste ao nÃquel. No segundo caso a reactivação da dermatite ocorreu seis horas após a ingestão de 10 mg de sulfato de nÃquel. A manutenção de dieta restritiva em alimentos com alto teor em nÃquel permitiu o desaparecimento total da dermatite e estabilização clÃnica que se mantém desde há 6 meses.
O diagnóstico de dermatite endógena induzida pela ingestão de nÃquel foi demonstrado através da realização de prova de provocação oral. A excreção de nÃquel através do suor parece ser relevante. A redução da ingestão diária de nÃquel, permitindo a menor concentração deste elemento no suor poderá explicar a melhoria da dermatite, particularmente, nas zonas cutâneas de maior sudação
- …