How farms' structures and sustainability standards shape land availability for energy crops. Study cases in West Africa

Sustainability is crucial for biofuels and bioenergy production in general. However, historically speaking, the biofuels industry has largely ignored sustainability criteria and consequently has been the source of considerable controversy. Despite a real expansion worldwide, biofuels development has still to face many barriers in the three pillars of sustainability. In the environmental domain, biofuels have to face accusations of deforestation, loss of biodiversity, carbon emission, water usage, etc. In the economic domain, they are accused to compete with other land uses for basic needs such as food and material , and they must prove that they are more viable than oil and other renewable energies. In the social domain, they also have to answer to complaints about land grabbing, rural poverty, social acceptance. Over the past twenty years, a large number of studies aimed to estimate the amount of bioenergy that can be produced in a sustainable manner. Results are very contrasted for many reasons mainly due to the heterogeneity of methodologies, definitions, assumptions and datasets employed. However, most studies agree that among all possible sources of biomass energy, energy crops are considered as the most important. Other crops and forest residues can also be good sources but do not reach the potential of energy crops. These studies lead to consider that the main potential contribution of biomass for energy production will depend on one hand of the energy crops yields and on the other hand on the quantity, the quality and the location of available land to cultivate. Considering that grassland, savannah or shrubland are idle or non-used land, most of the studies locate the majority of potentially available land in developing countries, in Sub-Saharan Africa and South America. But there is considerable debates about the availability of land in these regions and many authors point out the need for a clearer picture of what it means. Thus, land availability is maybe the most crucial parameters in sustainable potential assessment. But this concept of availability encompasses many interlinked factors and is lacking a clear definition. Depending on methodologies, availability may include technical or economic or social or legal or environmental factors, or multiple combinations of these different factors. However, since the 1990s, in order to guarantee the sustainability of the global bioenergy potential, several governments, NGOs and private companies have proposed ecological and social sustainability criteria which bioenergy has to fulfill. Since the early 2000s a set of voluntary standards have emerged in the Agro-food sector. They are produced through multi-stakeholder initiatives (MSI), which are presented as their main source of legitimacy. Many of these initiatives also called “Roundtables” are recognized and used in the sector of biofuel feedstock production : Roundtable for sustainable Palm Oil ( RSPO 2004), Roundtable for Responsible Soy (RTRS 2006), Better Sugar Cane Initiative (BSI), Better Cotton Initiative (BCI), and Round Table Sustainable Biofuels (RSB). All these standards have in common to define principles and criteria that restrain the availability of land dedicated to energy crops. They place restrictions on i) the types of land that may be used to grow energy crops and on ii) the social and technical models of production. According to these schemes availability of land is defined by criteria including technical factors (slope, soil, …), legal factors (land rights, respect of legal conservation areas), logistics factors (accessibility, distance to plants), environmental factors (high conservation values, carbon stocks), conversion factors (loss of biodiversity, zero deforestation), or food security factors (no competition with food crops), etc. These standards are still controversial and without doubt need to be improved, but in many countries including developing ones they currently drive feedstock production and therefore land availability for energy crops. The main objective of this paper is to propose a spatially explicit methodology to assess and analyze land availability for energy crops at national scale. The originality of this methodology is to start from existing sustainability standards of production and to translate principles and criteria into spatial constraints of availability. The methodological framework is applied in two West African countries : Mali and Burkina Faso. The application shows that taking into account farms structures and sustainable production rules reduces the land considered to be available by a factor of at least 4. The other key lesson is that family agriculture and contract farming may present viable alternatives to agro-industrial models. The advantage of this approach is that the scenarios built do not represent starting points of the assessment, but are rather one of the results. The scenarios and the production models are clearly formalized and thus represent topics of discussion which can be understood by producers and decision makers, allowing rules for the sustainable use of areas to be negotiated and refined

Stability of trailing vortices with radial stratification

We look at the effects of the radial density stratification on the stability of the q-vortex, a commonly accepted model for aircraft trailing vortices. It has been demonstrated that the 2D Lamb-Oseen vortex develops a Rayleigh-Taylor instability when its core is heavier than the surrounding uid (Joly,Fontane & Chassaing 2005, Sipp et al. 2005). The underlying mechanism relies on baroclinic vorticity generation due to any misalignment between the density gradient and the centripetal acceleration field. The instability is triggered provided that the density decreases radially somewhere in the vortex core. This mechanism is also active in the 3D trailing vortex and affects its stability characteristics due to the addition of an axial component in the acceleration field. We show that the unstable center modes of the homogeneous case (Fabre & Jacquin 2004) are promoted in a q-vortex with a heavy core. Their growth rate increases while their m-spiral structure is preserved. For an Atwood number At = 0:5, their predicted growth rate can be ten times the ones found in the homogeneous case. Furthermore, the unstable domain is extended far beyond the neutral curve in the homogeneous case, with unstable modes observed for Swirl numbers up to q = 5. It is argued here that corresponding density perturbations could eventually lead to the development of new and original strategies to decrease the lifespan of aircraft trailing vortices and greatly reduce their unwanted side-effects on contrails persistence and air traffic regulations

First Measurement of 72Ge(n,γ) at n_TOF

9th European Summer School on Experimental Nuclear AstrophysicsThe slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universo

Preparation and characterization of 33-S samples for 33-S(n,alpha)30-Si cross-section measurements at the n_TOF facility at CERN

Thin 33S samples for the study of the 33S(n,a)30Si cross-section at the n_TOF facility at CERN were made by thermal evaporation of 33S powder onto a dedicated substrate made of kapton covered with thin layers of copper, chromium and titanium. This method has provided for the first time bare sulfur samples a few centimeters in diameter. The samples have shown an excellent adherence with no mass loss after few years and no sublimation in vacuum at room temperature. The determination of the mass thickness of 33S has been performed by means of Rutherford backscattering spectrometry. The samples have been successfully tested under neutron irradiation.Ministerio de Economía y Competitividad de España-FPA2013-47327- C2-1-R, FPA2014-53290-C2-2-P, FPA2016-77689-C2-1-RJunta de Andalucía-P11-FQM-8229Ministerio de Economía y Empresa de España (Fondos FEDER)-FIS2015-69941-C2-1-PAECC (Asociación Española Contra el Cáncer)-PS16163811POR

Study of 12C(α,γ)16O reaction via the transfer reaction 12C(7Li,t)16O

International audienceThe 12C(a,g )16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of 12C(a,g )16O remains highly uncertain. The extrapolation of the measured cross sections to stellar energies (E=300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 (2+) and 7.12 (1−) MeV of 16O. In order to further investigate the contribution of these twosubthreshold resonances to the 12C(a,g )16O cross section, we performed a new determination of the a-reduced widths of the 6.92 and 7.12 MeV of 16O via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a-reduced widths for the 2+ and 1− sub-threshold states and their effect on the R-matrix calculations of 12C(a,g )16O

Recent results in nuclear astrophysics at the n_TOF facility at CERN

The neutron time of flight (n_TOF) facility at CERN is a spallation source characterized by a white neutron spectrum. The innovative features of the facility, in the two experimental areas, (20 m and 185 m), allow for an accurate determination of the neutron cross section for radioactive samples or for isotopes with small neutron capture cross section, of interest for Nuclear Astrophysics. The recent results obtained at n_TOF facility are presented

High precision measurement of the radiative capture cross section of 238U at the n-TOF CERN facility

The importance of improving the accuracy on the capture cross-section of 238U has been addressed by the Nuclear Energy Agency, since its uncertainty significantly affects the uncertainties of key design parameters for both fast and thermal nuclear reactors. Within the 7th framework programme ANDES of the European Commission three different measurements have been carried out with the aim of providing the 238U(n,γ) cross-section with an accuracy which varies from 1 to 5%, depending on the energy range. Hereby the final results of the measurement performed at the n TOF CERN facility in a wide energy range from 1 eV to 700 keV will be presented

The 236U neutron capture cross-section measured at the n-TOF CERN facility

The 236U isotope plays an important role in nuclear systems, both for future and currently operating ones. The actual knowledge of the capture reaction of this isotope is satisfactory in the thermal region, but it is considered insufficient for Fast Reactor and ADS applications. For this reason the 236U(n, γ) reaction crosssection has been measured for the first time in the whole energy region from thermal energy up to 1 MeV at the n TOF facility with two different detection systems: an array of C6D6 detectors, employing the total energy deposited method, and a 4π total absorption calorimeter (TAC), made of 40 BaF2 crystals. The two n TOF data sets agree with each other within the statistical uncertainty in the Resolved Resonance Region up to 800 eV, while sizable differences (up to 20%) are found relative to the current evaluated data libraries. Moreover two new resonances have been found in the n TOF data. In the Unresolved Resonance Region up to 200 keV, the n TOF results show a reasonable agreement with previous measurements and evaluated data

Measurement of the 241Am neutron capture cross section at the n-TOF facility at CERN

New neutron cross section measurements of minor actinides have been performed recently in order to reduce the uncertainties in the evaluated data, which is important for the design of advanced nuclear reactors and, in particular, for determining their performance in the transmutation of nuclear waste. We have measured the 241 Am(n,γ) cross section at the n TOF facility between 0.2 eV and 10 keV with a BaF2 Total Absorption Calorimeter, and the analysis of the measurement has been recently concluded. Our results are in reasonable agreement below 20 eV with the ones published by C. Lampoudis et al. in 2013, who reported a 22% larger capture cross section up to 110 eV compared to experimental and evaluated data published before. Our results also indicate that the 241 Am(n,γ) cross section is underestimated in the present evaluated libraries between 20 eV and 2 keV by 25%, on average, and up to 35% for certain evaluations and energy ranges.Plan Nacional I+D+I FPA2014-53290-C2-1Comisión Europea, ANDES FP7- 249671Comisión Europea, CHANDA FP7-60520