BEEKEEPING AND LOCAL SELF-RELIANCE IN RURAL SOUTHERN AFRICA*     

Pete M. Illgner  Etienne L. Nel  Mark P. Robertson 《Geographical review》1998,88(3):349-362

ABSTRACT. Beekeeping has the potential to supplement incomes in rural southern Africa. In light of regional economic constraints, self-reliance strategies that draw on local knowledge and skills take on a renewed importance. We consider the advantages and disadvantages of beekeeping and examine appropriate forms of development support. A short case study from Zimbabwe illustrates these issues.  相似文献   

Streamflow response to regional climate model output in the mountainous watershed: a case study from the Swiss Alps     

Kazi?RahmanEmail author  Christophe?Etienne  Ana?Gago-Silva  Chetan?Maringanti  Martin?Beniston  Anthony?Lehmann 《Environmental Earth Sciences》2014,72(11):4357-4369

Regional climate model (RCM) outputs are often used in hydrological modeling, in particular for streamflow forecasting. The heterogeneity of the meteorological variables such as precipitation, temperature, wind speed and solar radiation often limits the ability of the hydrological model performance. This paper assessed the sensitivity of RCM outputs from the PRUDENCE project and their performance in reproducing the streamflow. The soil and water assessment tool was used to simulate the streamflow of the Rhone River watershed located in the southwestern part of Switzerland, with the climate variables obtained from four RCMs. We analyzed the difference in magnitude of precipitation, maximum and minimum air temperature, and wind speed with respect to the observed values from the meteorological stations. In addition, we also focused on the impact of the grid resolution on model performance, by analyzing grids with resolutions of 50 × 50 and 25 × 25 km². The variability of the meteorological inputs from various RCMs is quite severe in the studied watershed. Among the four different RCMs, the Danish Meteorological Institute provided the best performance when simulating runoff. We found that temperature lapse rate is significantly important in the mountainous snow and glacier dominated watershed as compared to other variables like precipitation, and wind speed for hydrological performance. Therefore, emphasis should be given to minimum and maximum temperature in the bias correction studies for downscaling climatic data for impact modeling in the mountainous snow and glacier dominated complex watersheds.  相似文献   

Magnetic horizons of UHECR sources and the GZK feature     

Olivier Deligny  Antoine Letessier-Selvon  Etienne Parizot 《Astroparticle Physics》2004,21(6):609-615

We study the effect of random extra-galactic magnetic fields on the propagation of protons of energy larger than 10¹⁹ eV. We show that for reasonable field values (in the 100 nG range) the transition between diffusive and ballistic regimes occurs in the same energy range as the GZK cutoff (a few 10¹⁹ eV). The usual interpretation of the flux reduction above the GZK energy in terms of a sudden reduction of the visible horizon is modified. Moreover, since the size of the diffusion sphere of a continuous source of cosmic rays is of the order of 10 Mpc, the local structure of the Universe and, therefore, of potential local astrophysical sources plays a dominant role in the expected spectrum. Under reasonable assumptions on the sources configurations the expected GZK cutoff is reduced.  相似文献   

小型激光天文动力学空间计划概念   总被引：1，自引：0，他引：1  

倪维斗  朱进  武向平  褚桂柏  杨彬  高健  关敏  汤健仁  周翊  张中豪  黄天衣  曲钦岳  易照华  李广宇  陶金河  吴岸明  罗俊  叶贤基  周泽兵  熊耀恒  毕少兰  须重明  吴雪君  唐孟希  包芸  李芳昱  黄珹  杨福民  叶叔华  张书练  张元仲  聂玉昕  陈光  Joergen Christensen-Dalsgaard  Hansjoerg Dittus  Yasunori Fujii  Claus Laemmerzahl  Jean Francois Mangin  Achim Peters  Albrecht Ruediger  Etienne Samain  Stephan Schiller 《天文研究与技术》2002,(3):123-136

小型激光天文动力学空间计划是 :使用在太阳轨道上无拖曳航天器和地面站以激光干涉和脉冲测距的方法 ,精确地探讨天文动力学 ,检测相对论与时空基本定律 ,改进探测引力波的灵敏度以及更准确地测定太阳、行星和小行星的参数。 1 969年开始的月球激光 (反射 )测距 ,对地球物理、参考坐标的选定、相对论的检验均有重要的贡献。 3 0年来 ,激光技术的长足进步 ,使现在正是适合于开始进行研究空间有源 (主动 )测距和光波空间通讯的时候。激光天文动力学的兴起是必然的趋势 ,其精确度将比现在提高 3到 6个数量级 ,将是天文动力学革命性的发展。小型激光天文动力学空间计划可以起到带头作用。它的关键技术有三 ,即 :弱光锁相、极精确无拖曳航天和高衰减日冕仪。弱光锁相已有长足的进步。对高衰减日冕仪的研究 ,也有了初步的方案。LISA空间计划将于 2 0 0 6年 8月发射SMART -2 ,研究测试极精确无拖曳航天。小型激光天文动力学空间计划的关键技术已日趋成熟。在第一届国际激光天文动力学研讨会 ( 2 0 0 1 ,9.1 3 -2 3 )中介绍了各相关学科背景及前沿研究 ,讨论了激光天文动力学空间计划科学目标及相关技术 ,并召开了两次小型激光天文动力学空间计划预研究筹备会 ,建立了和欧洲的合作关系。会后着手进行此项对基础  相似文献   

Lander radioscience for obtaining the rotation and orientation of Mars     

Veronique Dehant  William Folkner  Etienne Renotte  Daniel Orban  Sami Asmar  Georges Balmino  Jean-Pierre Barriot  Jeremy Benoist  Richard Biancale  Jens Biele  Frank Budnik  Stefaan Burger  Olivier de Viron  Bernd Häusler  Özgur Karatekin  Sébastien Le Maistre  Philippe Lognonné  Michel Menvielle  Michel Mitrovic  Martin Pätzold  Marie Yseboodt 《Planetary and Space Science》2009,57(8-9):1050-1067

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space.Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers.A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia.The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level).The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO₂ in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO₂ sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.  相似文献   

The impact of dust on the scaling properties of galaxy clusters     

Antonio C. da Silva  rea Catalano  Ludovic Montier  Etienne Pointecouteau  Joseph Lanoux  Martin Giard 《Monthly notices of the Royal Astronomical Society》2009,396(2):849-859

We investigate the effect of dust on the scaling properties of galaxy clusters based on hydrodynamic N -body simulations of structure formation. We have simulated five dust models plus radiative cooling and adiabatic models using the same initial conditions for all runs. The numerical implementation of dust was based on the analytical computations of Montier & Giard. We set up dust simulations to cover different combinations of dust parameters that make evident the effects of size and abundance of dust grains. Comparing our radiative plus dust cooling runs with a purely radiative cooling simulation, we find that dust has an impact on cluster scaling relations. It mainly affects the normalization of the scalings (and their evolution), whereas it introduces no significant differences in their slopes. The strength of the effect critically depends on the dust abundance and grain size parameters as well as on the cluster scaling. Indeed, cooling due to dust is effective in the cluster regime and has a stronger effect on the 'baryon driven' statistical properties of clusters such as   L _X– M , Y – M , S – M   scaling relations. Major differences, relative to the radiative cooling model, are as high as 25 per cent for the   L _X– M   normalization, and about 10 per cent for the Y – M and S – M normalizations at redshift zero. On the other hand, we find that dust has almost no impact on the 'dark matter driven'   T _mw– M   scaling relation. The effects are found to be dependent in equal parts on both dust abundances and grain size distributions for the scalings investigated in this paper. Higher dust abundances and smaller grain sizes cause larger departures from the radiative cooling (i.e. with no dust) model.  相似文献   

Structural control over equilibrium silicon and oxygen isotopic fractionation: A first-principles density-functional theory study     

Merlin Méheut  Michele Lazzeri  Etienne Balan  Francesco Mauri 《Chemical Geology》2009,258(1-2):28-37

Isotopic fractionation factors for oxygen and silicon in selected silicates (quartz, enstatite, forsterite, lizardite, kaolinite) are calculated using first-principles methods based on density-functional theory. Good agreement between theory and experiment is found in the case of oxygen. In the case of silicon, agreement and differences with existing estimates of equilibrium fractionation factors are discussed. The relationship between silicon and oxygen fractionation factors, silicate polymerization degree and chemical composition is studied and compared with previous semi-empirical models.  相似文献   

Evidence of multiple evaporite recycling processes in a salt‐tectonic context,Sivas Basin,Turkey          下载免费PDF全文

Alexandre Pichat  Guilhem Hoareau  Jean‐Paul Callot  Etienne Legeay  Kaan Sevki Kavak  Sidonie Révillon  Corinne Parat  Jean‐Claude Ringenbach 《地学学报》2018,30(1):40-49

The isotopic composition of evaporites can shed light on their environment of precipitation and their subsequent recycling processes. In this study, we performed Sr, O and S isotopic analyses on evaporitic sulphates in the halokinetic Sivas Basin. The main objectives were to decipher the age and origin of the evaporites responsible for the salt tectonics, and to test whether diapir dissolution acts as the source of younger evaporitic layers in continental mini‐basins. The Sr isotopes demonstrate that the first evaporites precipitated from seawater during the Middle–Late Eocene. The similar isotopic values measured in the halokinetic domain confirm that the Eocene evaporites triggered the salt tectonics and were continuously recycled in Oligo‐Miocene mini‐basins as lacustrine to sabkha evaporites. Modern halite precipitates suggest that the dissolution and recycling of diapiric halite is ongoing. This study demonstrates the efficiency of isotopic analyses in constraining evaporite recycling processes in continental halokinetic domains.  相似文献   

Momentum- and Heat-Flux Parametrization at Dome C,Antarctica: A Sensitivity Study     

Etienne Vignon  Christophe Genthon  Hélène Barral  Charles Amory  Ghislain Picard  Hubert Gallée  Giampietro Casasanta  Stefania Argentini 《Boundary-Layer Meteorology》2017,162(2):341-367

An extensive meteorological observational dataset at Dome C, East Antarctic Plateau, enabled estimation of the sensitivity of surface momentum and sensible heat fluxes to aerodynamic roughness length and atmospheric stability in this region. Our study reveals that (1) because of the preferential orientation of snow micro-reliefs (sastrugi), the aerodynamic roughness length \(z_{0}\) varies by more than two orders of magnitude depending on the wind direction; consequently, estimating the turbulent fluxes with a realistic but constant \(z_{0}\) of 1 mm leads to a mean friction velocity bias of \(24\,\%\) in near-neutral conditions; (2) the dependence of the ratio of the roughness length for heat \(z_{0t}\) to \(z_{0}\) on the roughness Reynolds number is shown to be in reasonable agreement with previous models; (3) the wide range of atmospheric stability at Dome C makes the flux very sensitive to the choice of the stability functions; stability function models presumed to be suitable for stable conditions were evaluated and shown to generally underestimate the dimensionless vertical temperature gradient; as these models differ increasingly with increases in the stability parameter z / L, heat flux and friction velocity relative differences reached \(100\,\%\) when \(z/L > 1\); (4) the shallowness of the stable boundary layer is responsible for significant sensitivity to the height of the observed temperature and wind data used to estimate the fluxes. Consistent flux results were obtained with atmospheric measurements at heights up to 2 m. Our sensitivity study revealed the need to include a dynamical parametrization of roughness length over Antarctica in climate models and to develop new parametrizations of the surface fluxes in very stable conditions, accounting, for instance, for the divergence in both radiative and turbulent fluxes in the first few metres of the boundary layer.  相似文献   

The dictionary of human geography, 5th edition – Edited by Derek Gregory,Ron Johnston,Geraldine Pratt,Michael J. Watts and Sarah Whatmore     

Etienne Nel 《New Zealand geographer》2010,66(3):234-236

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