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ECONOMETRIC METHODS FOR LAND USE MICROSIMULATION
No full textTypically, urban development models have been based on aggregate principles. UrbanSim (Waddell et al. 2003) is among a new breed of models that use microsimulation in an effort to overcome the limitations of earlier models and provide a more dynamic and detailed paradigm. The advantages and disadvantages of using microsimulation are not within the scope of this chapter, but the main implication is that more data, as well as more detailed ones are required for microsimulation than for aggregate models. In the context of the SustainCity project (http://www.sustaincity.org), three European cities (Brussels, Paris and Zürich, described in other chapters of this handbook) have been modelled using the land use microsimulation platform UrbanSim. This platform relies on various models interacting with each other, to predict long–term urban development. The aim of this chapter is to provide some econometric insight into this process. A common set of notations and assumptions are first defined, and the more common model structures (linear regression, multinomial logit, nested logit, mixed MNL and latent variable models) are described in a consistent way. Special treatments and approaches that are required due to the specific nature of the data in this type of applications (i.e. involving very large number of alternatives, and often exhibiting endogeneity, correlation, and (pseudo–)panel data properties) are discussed. For example, importance sampling, spatial econometrics, Geographically Weighted Regression (GWR) and endogeneity issues are covered. Specific examples of the following models: (i) household location choice model, (ii) jobs location/firmography, (iii) real estate price model, and (iv) land developmentmodel, are demonstrated in the context of the case studies in Brussels, Paris and Zürich. Finally, lessons learned in relation to the econometric models from these case studies are summarized
Room-temperature creep and stress relaxation in commercial purity titanium– Influence of the oxygen and hydrogen contents onincubation phenomena and aging-induced rejuvenation of thecreep potential
No full textInternational audienceCreep and stress relaxation tests were run at room-temperature along the rolling and transverse directions in three batches of titanium with different solute oxygen and hydrogen contents. Oxygen-induced dynamic strain aging was shown to hinder creep at low stress level and solute hydrogen to enhance it and to promote a dramatic aging-induced rejuvenation of the creep potential. Primary creep could be described by a single power law equation in which both the anisotropy and the influence of the oxygen content were taken into account. Secondary creep rates varied exponentially with the applied stress, in the same way along rolling and transverse directions, but with a stress dependency which increased with the oxygen content. Creep of commercial purity titanium was controlled mainly by screw dislocations with a Burgers vector gliding on prismatic and pyramidal planes, while for a Ti batch with a lower oxygen content and larger grain size, mechanical twinning also contributed to the creep strain. 33 to 40% of the flow stress was relaxed within 20 hours, according to logarithmic kinetics, which did not depend on the loading direction or oxygen content
Apport de la modélisation en organocatalyse : sélectivités, mécanismes et propriétés.
No full textNowadays, molecular modelling, and more particularly density functional theory methods (DFT), is a great way to describe and rationalize properties of chemical systems. In this work, we used these computational methods to study organocatalyzed reactions. Organocatalysis, which is part of the green chemistry field by the absence of metal atoms, proved to be a very successful mode of catalysis over the last decade in terms of yields, but also in terms of enantiomeric excesses when using a chiral catalyst. In this thesis we were interested in two types of organocatalysts : phosphines and phosphoric acids. Phosphines catalyze the reaction between a conjugated diene and an imine, yielding a pyrroline in a selective manner. The understanding of the regioselectivity of this reaction was the main topic of our theoretical study, in which we modelled different possible reaction pathways. These theoretical works were joined by experimental kinetic measures which allowed us to confirm the rate-determining step of the reaction. These studies lead us to propose a new reaction mechanism which explains the experimental results observed in the literature. Phosphoric acids catalyze the enantioselective reduction of quinolines by Hantzsch esters. A complete theoretical study of the mechanism of this reaction allowed us to reproduce the enantiomeric excesses obtained experimentally. On this basis, we were also interested in the rationalization between the chemical properties of these phosphoric acids and their ability to catalyze reactions.La modélisation moléculaire, et plus particulièrement les méthodes issues de la théorie de la fonctionnelle de la densité (DFT), est devenue actuellement un partenaire privilégié pour la description et la rationalisation des propriétés des systèmes chimiques. Dans le cadre de ces travaux de thèse, nous avons utilisé ces outils pour étudier des réactions issues de l’organocatalyse. Ce mode de catalyse, classé dans le domaine de la chimie vert du fait de l’absence d’atomes métalliques, s’est démarqué au cours de ces dernières décennies par ses excellentes performances en termes de rendements, mais aussi d’excès énantiomériques en utilisant un catalyseur chiral. Nous nous sommes intéressés au cours de cette thèse à deux grands types d’organocatalyseurs : les phosphines et les acides phosphoriques. Les phosphines catalysent la réaction entre un diène conjugué et une imine, produisant une pyrroline de façon sélective. La compréhension de la régiosélectivité de cette réaction a été au centre de notre étude théorique, au cours de laquelle nous avons modélisé les différents chemins réactionnels envisageables. Cette partie théorique a été accompagnée de mesures cinétiques expérimentales qui ont permis de confirmer l’étape déterminante de la réaction. L’ensemble de ces travaux nous a conduits à proposer un nouveau mécanisme réactionnel expliquant les résultats expérimentaux de la littérature. Les acides phosphoriques catalysent la réaction de réduction de quinoline par un ester de Hantzsch de façon énantiosélective. Seul un réexamen complet du mécanisme de cette réaction nous a permis, par modélisation, de reproduire les excès énantiomériques expérimentaux. Sur cette base, une rationalisation entre les propriétés physico-chimiques des acides phosphoriques et leurs capacités catalytiques a pu être envisagée
The isotopic composition of water vapour and precipitation in Ivittuut, southern Greenland
No full textInternational audienceSince September 2011, a wavelength-scanned cavity ring-down spectroscopy analyser has been remotely operated in Ivittuut, southern Greenland, providing the first record of surface water vapour isotopic composition based on continuous measurements in South Greenland and the first record including the winter season in Greenland. The comparison of vapour data with measurements of precipitation isotopic composition suggest an equilibrium between surface vapour and precipitation. <br><br> d18O and deuterium excess are generally anti-correlated and show important seasonal variations, with respective amplitudes of ~10 and ~20&permil;, as well as large synoptic variations. The data depict small summer diurnal variations. At the seasonal scale, d18O has a minimum in November-December and a maximum in June-July, while deuterium excess has a minimum in May-June and a maximum in November. The approach of low-pressure systems towards South Greenland leads to d18O increase (typically +5&permil;) and deuterium excess decrease (typically -15&permil;). Seasonal and synoptic variations coincide with shifts in the moisture sources, estimated using a quantitative moisture source diagnostic based on a Lagrangian back-trajectory model. The atmospheric general circulation model LMDZiso correctly captures the seasonal and synoptic variability of d18O, but does not capture the observed magnitude of deuterium excess variability. Covariations of water vapour isotopic composition with local and moisture source meteorological parameters have been evaluated. d18O is strongly correlated with the logarithm of local surface humidity, consistent with Rayleigh distillation processes, and with local surface air temperature, associated with a slope of ~0.4% °C-1. Deuterium excess correlates with local surface relative humidity as well as surface relative humidity from the dominant moisture source area located in the North Atlantic, south of Greenland and Iceland. © Author(s) 2014
From Voyager-IRIS to Cassini-CIRS: Interannual variability in Saturn’s stratosphere?
No full textInternational audienceWe present an intercomparison of Saturn’s stratosphere between Voyager 1-IRIS observations in 1980 and Cassini-CIRS observations in 2009 and 2010. Over a saturnian year (∼29.5 years) has now passed since the Voyager flybys of Saturn in 1980/1981. Cassini observations in 2009/2010 capture Saturn in the same season as Voyager observations (just after the vernal equinox) but one year later. Any differences in Saturn’s atmospheric properties implied by a comparison of these two datasets could therefore reveal the extent of interannual variability. We retrieve temperature and stratospheric acetylene and ethane concentrations from Voyager 1-IRIS (View the MathML sourceΔν̃=4.3cm-1) observations in 1980 and Cassini-CIRS (View the MathML sourceΔν̃=15.5cm-1) ‘FIRMAP’ observations in 2009 and 2010. We observe a difference in temperature at the equator of 7.1 ± 1.2 K at the 2.1-mbar level that implies that the two datasets have captured Saturn’s semiannual oscillation (SSAO) in a slightly different phase suggesting that its period is more quasi-semiannual. Elevated concentrations of acetylene at 25°S in 1980 with respect to 2010 imply stronger downwelling at the former date which may also be explained by a difference in the phase of the SSAO and its dynamical forcing at low latitudes. At high-southern and high-northern latitudes, stratospheric temperatures and hydrocarbon concentrations appear elevated in 1980 with respect to 2009/2010. This could be an artefact of the low signal-to-noise ratio of the corresponding observations but might also be explained by increased auroral activity during solar maximum in 1980
APIFLAME v1.0: high-resolution fire emission model and application to the Euro-Mediterranean region
No full textInternational audienceThis paper describes a new model for the calculation of daily, high-resolution (up to 1 km) fire emissions, de-veloped in the framework of the APIFLAME (Analysis and Prediction of the Impact of Fires on Air quality ModEling) project. The methodology relies on the classical approach, multiplying the burned area by the fuel load consumed and the emission factors specific to the vegetation burned. Emis-sions can be calculated on any user-specified domain, hor-izontal grid, and list of trace gases and aerosols, providing input information on the burned area (location, extent), and emission factors of the targeted species are available. The applicability to high spatial resolutions and the flexibility to different input data (including vegetation classifications) and domains are the main strength of the proposed algorithm. The modification of the default values and databases proposed does not require any change in the core of the model. The code may be used for the calculation of global or regional inventories. However, it has been developed and tested more specifically for Europe and the Mediterranean area. A regional analysis of fire activity and the resulting emissions in this region is provided. The burning season ex-tends from June to October in most regions, with generally small but frequent fires in eastern Europe, western Russia, Ukraine and Turkey, and large events in the Mediterranean area. The resulting emissions represent a significant frac-tion of the total yearly emissions (on average amounting to ∼ 30 % of anthropogenic emissions for PM 2.5 , ∼ 20 % for CO). The uncertainty regarding the daily carbon emissions is estimated at ∼ 100 % based on an ensemble analysis. Con-sidering the large uncertainties regarding emission factors, the potential error on the emissions for the various pollutants is even larger. Comparisons with other widely used emission inventories show good correlations but discrepancies of a fac-tor of 2–4 in the amplitude of the emissions, our results being generally on the higher end
Transverse dynamics of an intense electron bunch traveling through a pre-ionized plasma
No full textInternational audienceThe propagation of a relativistic electron bunch through a plasma is an important problem in both plasma-wakefield acceleration and laser-wakefield acceleration. In those situations, the charge of the accelerated bunch is usually large enough to drive a relativistic wakefield, which then affects the transverse dynamics of the bunch itself. Yet to date, there is no fully relativistic, fully electromagnetic model that describes the generation of this wakefield and its feedback on the bunch. In this article, we derive a model which takes into account all the relevant relativistic and electromagnetic effects involved in the problem. A very good agreement is found between the model and the results of particle-in-cell simulations. The implications of high-charge effects for the transport of the bunch are discussed in detail
Physical processes at work in sub-30fs, PW laser pulse-driven plasma accelerators: Towards GeV electron acceleration experiments at CILEX facility
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Electron acceleration in sub-relativistic wakefields driven by few-cycle laser pulses
No full textInternational audienceUsing Particle-in-Cell simulations, we study the interaction of few mJ-few cycle laser pulses with an underdense plasma at resonant density. In this previously unexplored regime, it is found that group velocity dispersion is a key ingredient of the interaction. The concomitant effects of dispersion and plasma nonlinearities causes a deceleration of the wakefield phase velocity, which becomes sub-relativistic. Electron injection in this sub-relativistic wakefield is enhanced and leads to the production of a femtosecond electron bunch with picocoulomb of charge in the 5-10 MeV energy range. Such an electron bunch is of great interest for application to ultrafast electron diffraction. In addition, in this dispersion dominated regime, it is shown that positively chirped laser pulses can be used as a tuning knob for compensating plasma dispersion, increasing the laser amplitude during self-focusing and optimizing the trapped charge
Engagement décennal ou endettement étudiant ? Les bi-admis ENS Cachan/HEC face au choix de leur école et de leur carrière
No full textOwing to the international competition between colleges, tuition fees keep rising. Whereas the top French business school HEC (École des hautes études commerciales de Paris) leads this trend in France, the Écoles normales supérieures (ENS) is unique in that its students are paid as civil servants. This article tackles how the cost of studies plays a part in students’ choices. To deal with this question, we have conducted several semi-structured interviews with successful candidates at both HEC and ENS Cachan following their economics and business preparatory classes.Hence we look beyond economic analysis and study students’ own portrayals of their studies. Typically, the cost of studies is strongly linked to job market prospects after graduation, as predicted by students when choosing their school. Therefore, the prospect of a lucrative job required due to heavy student debt may be considered a less attractive option than the ten-year commitment signed with the French state.Dans un contexte de mise en concurrence internationale des grands établissements universitaires, l’instauration ou le relèvement des frais de scolarité semble être une évolution inéluctable. Les Écoles normales supérieures (ENS), avec leurs élèves fonctionnaires, apparaissent singulières. Dans cet article, nous étudions comment le coût des études intervient dans les choix des étudiants. Une série d’entretiens semi-directifs menés auprès d’étudiants admis à la fois à l’ENS Cachan et à l’École des hautes études commerciales de Paris (HEC) à l’issue de classes préparatoires commerciales nous permet d’appuyer et d’illustrer nos analyses sur une population pour laquelle l’accès au crédit est assuré. Nous nous intéressons en particulier à ce qui se joue, au-delà de l’aspect purement économique, dans les représentations que se font les étudiants de leurs études. Nous montrons que la question du coût interfère fortement avec celle des débouchés, une interaction anticipée par les étudiants au moment de leur choix de parcours dans l’enseignement supérieur. Dès lors, la perspective d’un emploi fortement rémunérateur imposé par l’endettement étudiant peut-elle apparaître pour certains comme une contrainte bien plus lourde qu’un engagement décennal signé avec l’État