La croissance démographique ou accroissement démographique ou variation totale de population est la différence entre l’effectif d’une population à la fin et au début d’une période donnée (généralement un an). Elle peut être exprimée par le taux d'évolution du nombre d’individus au sein d’une population par unité de temps et pour aussi n’importe quelle espèce (animale ou végétale, par exemple). Elle se décompose en deux parties distinctes :

l’accroissement naturel ;

le solde migratoire.

Si la somme de ces deux composantes est négative, la croissance de la population sera alors négative (c'est la décroissance démographique). Une démographie peut également être stable avec une croissance démographique nulle. Taux d’accroissement démographique En démographie, la « croissance démographique » est l'évolution de la taille d'une population pour un territoire donné, le « taux d’accroissement démographique » décrit le rythme de cette évolution (augmentation ou diminution

Constructing the desert. Hotel and coach station (Ouarzazate, Maroc)

Pietro Berta, Adèle Moret

Desertification process keeps on expanding, particularly on the African continent, arid areas cover one third of the surface. At the same time, the world human population increases exponentially. For these reasons, it is important to keep on exploiting these desert zones. Ouarzazate is situated in the south of Morocco in a sub-desert climate. The city is nicknamed “Door of the desert” because of its strategic location: it is situated at the junction of the two roads, which give accessibility to the south of Morocco and the Sahara desert. The region is well known for its architectural patrimony and more recently for the cinema activities. These two different domains make increase the number of visitors in this part of the country and there will soon be a lack of host infrastructure including hotels. The project, a hotel and a coach station, doesn't want to be closed-off on itself, but to take place in the city centre to benefit of the existing activities; at the same time the two programs are close to the main crossroad of the region. This situation is accorded with the way tourists travel in the region: moving a lot in order to discover a maximum of sites spread in the south and staying a short time in the same place. The hotel is inspired by the caravanserai, which was a roadside inn along the trade routes where travellers could rest and recover from the day's journey. It supported the flow of commerce, information and people. It was a place where travellers could acquire new supplies and there were also shops where merchants could dispose of some of their goods. The issue of this project in the desert is to build in a sustainable way using contemporary building construction modes being in the same time inspired by vernacular architecture.

2009

Magnetic Properties of Surface Adsorbed Metal Adatoms and Dimers

Dante Philippe Sblendorio

This thesis investigates the magnetic properties of single atoms and dimers adsorbed on graphene and oxide decoupling layers supported by single crystal metal substrates, using scanning tunneling microscopy (STM) and spin-polarized scanning tunneling microscopy (SP-STM). The goal is twofold: to use SP-STM to further advance the understanding of the interactions that determine the magnetic stability of Dy adatoms on graphene/Ir(111) and Ho adatoms on MgO/Ag(100), and to use insights from these systems to motivate the study of new systems-- mainly, IrCo heterodimers on graphene/Ir(111).For Dy adatoms on graphene/Ir(111), the characteristic lifetime of the spin system is measured as a function of temperature and tunnel bias, probing the available magnetization reversal pathways in the energy level diagram. The necessity of including the intra-atomic exchange to correctly describe spin lifetimes is demonstrated. In addition, naturally abundant Dy isotopes possess two possible nuclear spin values. Models of both nuclear spin cases of Dy are compared, and shown to produce similar behavior in the temperature and bias ranges probed by SP-STM. Furthermore, accounting for both nuclear spin cases allows for modeling of X-ray magnetic circular dichroism (XMCD) magnetization sweeps. For Ho adatoms on MgO/Ag(100), novel measurement protocols are used to determine the zero-field stability, and the correct ground state model. These protocols are also used to induce magnetic state reversal via Landau-Zener tunneling at avoided level crossings due to the hyperfine interaction. Finally, the study of the IrCo heterodimer adsorbed on graphene is motivated with stability considerations derived from the studies of Dy adatoms on graphene/Ir(111) and Ho adatoms on MgO/Ag(100), in addition to calculations based on density function theory (DFT). Strategies of engineering these heterodimers using statistical growth and atomic manipulation are successfully implemented. The heterodimer is highly mobile on graphene/Ir(111) and displays geometric instability, consistent with its predicted upstanding geometry. Despite this, measurement via STM and SP-STM is demonstrated. Observations are consistent with the robust magnetic stability expected from DFT studies, but additional investigation is needed to disentangle the measurements made thus far.

EPFL2022

Effects of different soil amendments on phytoremediation from a cadmium and DDTs co-contaminated soil by Sedum alfredii (Cd hyperaccumulator) co-cropped with Ricinus communis (DDT accumulator)

Pauline Grandjean

Soil pollution is a major environmental problem actually in China and in the world. It increases environmental risks and can affect humans through the food chain. Like solutions to clean-up the soils are generally expensive and can have side effects on environment, phytoremediation, an environmental friendly technology is a good alternative to traditional remediation. Nevertheless, some improvements must be done to increase its efficiency and make it economically viable. The goal of this work is to study two strategies respectful of the environment to improve the efficiency of phytoremediation: the co-cropping and the addition of amendments. Two Chinese species, Sedum alfredii (hyperaccumulator of cadmium) and Ricinus communis (accumulator of DDT) were co-cropped in pots with a soil contaminated by cadmium and DDT, in which different amendments (rapeseed waste, pig manure, a bio-surfactant: tea saponin, one of its by-product, and sulfur) were added to observe if they increase the efficiency of the phytoremediation. Bacteria were also used to improve DDT degradation. If the ricinus grew fast and easily, sedum biomass was very low and seems not suitable for co-cropping in these conditions. The rapeseed waste inhibit the growth of plants, suggesting that the dose was probably to high. Other amendments allowed a relatively similar growth with sensitively the best for tea saponin and microbes do not affect significantly the biomass. After determined in laboratory that tea saponin enhance the desorption of DDT and Cd in soil, an other pot experiment was started with Ricinus communis in soil amended with different concentrations of saponin to see if it also improve the phytoremediation. In the future, if the addition of amendments can enhance the phytoremediation as expected, analysis of parameters such as the quantity of nutrients or pollutants bioavailable or the structure of dissolve organic matter (DOM) might be done to see if they can explain this phenomenon. Further analysis in field conditions and with optimal concentrations of amendments are needed to determine if and in which conditions these strategies can be applicable at large scale.

2011