نتایج جستجو برای: Sahara

تعداد نتایج: 2126  

2017
Jessica E Tierney Francesco S R Pausata Peter B deMenocal

During the "Green Sahara" period (11,000 to 5000 years before the present), the Sahara desert received high amounts of rainfall, supporting diverse vegetation, permanent lakes, and human populations. Our knowledge of rainfall rates and the spatiotemporal extent of wet conditions has suffered from a lack of continuous sedimentary records. We present a quantitative reconstruction of western Sahar...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2011
Nick A Drake Roger M Blench Simon J Armitage Charlie S Bristow Kevin H White

Evidence increasingly suggests that sub-Saharan Africa is at the center of human evolution and understanding routes of dispersal "out of Africa" is thus becoming increasingly important. The Sahara Desert is considered by many to be an obstacle to these dispersals and a Nile corridor route has been proposed to cross it. Here we provide evidence that the Sahara was not an effective barrier and in...

2009
Widodo John H. Patterson Ed Newbigin Mark Tester Antony Bacic Ute Roessner

Plants show varied cellular responses to salinity that are partly associated with maintaining low cytosolic Na(+) levels and a high K(+)/Na(+) ratio. Plant metabolites change with elevated Na(+), some changes are likely to help restore osmotic balance while others protect Na(+)-sensitive proteins. Metabolic responses to salt stress are described for two barley (Hordeum vulgare L.) cultivars, Sa...

2017
Rosemarie Kentie Rocío Marquez-Ferrando Jordi Figuerola Laura Gangoso Jos C E W Hooijmeijer A H Jelle Loonstra Frédéric Robin Mathieu Sarasa Nathan Senner Haije Valkema Mo A Verhoeven Theunis Piersma

Migrating long distances requires time and energy, and may interact with an individual's performance during breeding. These seasonal interactions in migratory animals are best described in populations with disjunct nonbreeding distributions. The black-tailed godwit (Limosa limosa limosa), which breeds in agricultural grasslands in Western Europe, has such a disjunct nonbreeding distribution: Th...

Journal: :Biology letters 2016
Janne Ouwehand Christiaan Both

Each year more than two billion songbirds cross the Sahara, but how they perform this formidable task is largely unknown. Using geolocation tracks from 27 pied flycatchers, a nocturnally migrating passerine, we show that most birds made diurnal flights in both autumn and spring. These diurnal flights were estimated to be part of non-stop flights of mostly 40-60 h. In spring, birds flew across t...

Journal: :J. Economic Theory 2011
An Chen Antoon Pelsser Michel Vellekoop

We develop a new class of utility functions, SAHARA utility, with the distinguishing feature that it allows absolute risk aversion to be non-monotone and implements the assumption that agents may become less risk-averse for very low values of wealth. The class contains the well-known exponential and power utility functions as limiting cases. We investigate the optimal investment problem under S...

2003
H. Renssen V. Brovkin H. Goosse

[1] The termination of the Holocene African Humid Period ( 9 to 6 kyr BP) is simulated with a threedimensional global coupled climate model that resolves synoptic variability associated with weather patterns. In the simulation, the potential for ‘‘green’’ and ‘‘desert’’ Sahara states becomes equal between 7.5 and 5.5 thousand years ago, causing the climate system to fluctuate between these stat...

Journal: :Proceedings of the National Academy of Sciences of the United States of America 2003
Christophe J Douady François Catzeflis Jaishree Raman Mark S Springer Michael J Stanhope

Although the Sahara is a major geographical feature of the African continent, its role in the diversification of animal species is not well understood. We present here a molecular phylogeny for members of the endemic African mammalian order Macroscelidea (elephant shrews) with molecular-clock calculations; this molecular phylogeny provides convincing evidence that the genus Elephantulus is diph...

Journal: :Encyclopédie berbère 1991

Journal: :Tensões Mundiais 2018

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