The mystery of the end of the green Sahara

Mit dem Erdsystemmodell des Max-Planck-Instituts für Meteorologie haben wir die Änderungen im globalen Klimasystem während der letzten 8000 Jahre in einer räumlich detaillierten Darstellung berechnet. So konnten wir einen Teil des Rätsels um das Ende der grünen Sahara lösen. Rekonstruktionen zeigen ein komplexes Änderungsmuster. In unserer Simulation wird das Ende der feuchten Phase nicht nur vom Rückzug des Monsuns, sondern auch von der Änderung der Zugbahn extratropischer Tiefdruckgebiete bestimmt. Als deren Zusammenspiel vor rund 4000 Jahren aufbrach, nahmen Niederschlag und Vegetation in der Westsahara rasch abWith the Earth System Model of the Max Planck Institute for Meteorology we have calculated the changes in the global climate system during the last 8000 years in a spatially detailed representation. This enabled us to solve part of the mystery about the end of the green Sahara. Reconstructions show a complex structure. In our simulation, the end of the humid phase is determined not only by the retreat of the monsoon but also by the change in the path of extratropical troughs. When their interplay broke up about 4000 years ago, the precipitation and vegetation in the Western Sahara rapidly decreased

Contribution of oceanic and vegetation feedbacks to Holocene climate change in monsoonal Asia

The impact of vegetation-atmosphere and ocean-atmosphere interactions on the mid- to late Holocene climate change as well as their synergy is studied for different parts of the Asian monsoon region, giving consideration to the large climatic and topographical heterogeneity in that area. We concentrate on temperature and precipitation changes as the main parameters describing monsoonal influenced climates. For our purpose, we analyse a set of coupled numerical experiments, performed with the comprehensive Earth system model ECHAM5/JSBACH-MPIOM under present-day and mid-Holocene (6 k) orbital configurations (Otto et al., 2009b). The temperature change caused by the insolation forcing reveals an enhanced seasonal cycle, with a pronounced warming in summer (0.58 K) and autumn (1.29 K) and a cooling in the other seasons (spring: -1.32 K; winter: -0.97 K). Most of this change can be attributed to the direct response of the atmosphere, but the ocean, whose reaction has a lagged seasonal cycle (warming in autumn and winter, cooling in the other seasons), strongly modifies the signal. The simulated contribution of dynamic vegetation is small and most effective in winter, where it slightly warms the near-surface atmosphere (approx. 0.03 K). The temperature difference attributed to the synergy is on average positive, but also small. Concerning the precipitation, the most remarkable change is the postponement and enhancement of the Asian monsoon (0.46 mm/day in summer, 0.53 mm/day in autumn), mainly related to the direct atmospheric response. On regional average, the interactive ocean (ca. 0.18 mm/day) amplifies the direct effect, but tends to weaken the East Asian summer monsoon and strongly increases the Indian summer monsoon rainfall rate (0.68 mm/day). The influence of dynamic vegetation on precipitation is comparatively small (<0.04 mm/day). The synergy effect has no influence, on average

Stoner vs. spin-mixing behavior in the bulk magnetism of Gd: a spin-resolved photoemission study

The temperature dependence of the rare-earth Δ2-bulk band has been regarded as an exemplary case which realizes the simple Stoner behavior. We examined the evolution of GdΔ2 bulk bands with temperature in the range 0.5≤ T/TC≤ 1 with spin-resolved, photoemission spectroscopy. The direct observation of the spin-dependent spectral line shapes reveals a complex temperature dependence and manifests a clear inadequacy of the Stoner model to the description of the magnetism in rare earths

Finite temperature magnetism in Gd: evidence against a Stoner behavior

The temperature dependence of the rare-earth valence bands has been regarded as a realization of the Stoner behavior. The exchange splitting of the electronic states appears to scale as the magnetic order parameter for T<TC and to vanish at T = TC. We report here a spin-resolved photoemission study on the evolution of Gd bulk bands for 0.5≤ T/TC≤ 1. The spin-polarized spectral line shapes display a complex temperature dependence, which clearly contrasts with the interpretation of previous experimental results. The spin-resolved photoemission data demonstrate the inadequacy of the Stoner model to the description of magnetism in rare earths

Alteração do campo visual em função do uso de cabinas em tratares agrícolas.

Com o objetivo de avaliar a alteração do campo visual de um trator, ocasionada pela instalação de uma cabina, foram determinadas as áreas de visibilidade nula em função da presença ou não da mesma, para cada campo visual. Os procedimentos adotados basearam-se na norma ISO 5721-1981 - Agricultural tractors - Operator's field of vision. A cabina aumentou em 34,42% a área de visibilidade nula. A relação área de projeção do trator/área total sombreada foi de 0,075 para o trator sem cabina, e 0,057 para o trator com cabina, indicando as melhores condições de visibilidade do primeiro em relação ao segundo. No que se refere aos campos visuais, a maior redução ocorreu no campo visual dos olhos e no obtido com o movimento da cabeça, em função dos suportes da cabina e da estrutura de proteção contra o capotamento. A cabina diminui o campo de visão do operador, e adequações no projeto da estrutura avaliada são necessárias para melhorar as condições de visibilidade. ALTERATION OF THE VISUAL FIELD IN FUNCTION OF THE USE OF CABINS IN AGRICULTURAL TRACTORS. Aiming to evaluate the alteration of the visual field of a tractor occasioned by the installation of a cabin were determined the null visibility areas due to the presence or not of this structure, for each visual field. The procedures adopted were based on ISO 5721-1981 - Agricultural tractors - Operator's field of vision. The cabin increased in 34,42% the area of null visibility. The relationship projection area of tractor/total shadowed area was 0,075 to the tractor without a cabin, and 0,057 for the tractor with cabin, indicating the best conditions of visibility of the first in relation to the second. With respect to the visual area, the largest reduction happened in the eyes visual field and in the obtained with the head movement in function of the cabin supports and the rollover protection structure. The cabin decreases the operator?s area of vision, and adjustments in the project of the structure evaluated are necessary to improve the visibility conditions

Magnetism and interlayer coupling in fcc Fe/Co films

The magnetism of epitaxial fee Fe films deposited on Co(100) and sandwiched between two Co(100) films was investigated by x-ray magnetic circular dichroism. The dependence of the Fe magnetism on the film thickness is complex and qualitatively similar on Co(100) and in fee Co/Fe/Co(100) trilayers. The fee Fe film magnetization presents a pronounced oscillation, suggesting a partial antiferromagnetic ordering in the 5-10 monolayer thickness range. The fee Fe films mediate an oscillatory, indirect coupling in Co/Fe/Co(100) structures that alternates in correspondence with the changes of the Fe magnetization

Exploring International Law: Opportunities and Challenges for Political Science Research

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148360/1/1521-9488.00223.pd