Achieving a Jobs-Housing balance in the Paris region - the potential of reducing car trafic

Many experts believe that the uninterrupted lengthening of trip distances, and especially trip-to-work distances, is carried mostly by urban sprawl combined to growing functional (economic functions/residential functions) and social (high-class residential areas/low-class residential areas) specialization of urban space. According to them, these three dynamics (urban sprawl - functional specialization - social specialization) drag along quantitative and qualitative spatial imbalances between economic and residential functions and these spatial imbalances contribute to widen the distance separating workers' homes and job places, and hence, to lenghten the trips-to-work. On the basis of this diagnosis, the re-establishement of a greater balance, on both quantitative and qualitative grounds, between jobs and housing in different areas of the city is currently emerging as a major issue regarding the car-traffic reducing goal. Making the assumption that the multiplication of long-distance trips occurs as a consequence of greater difficulties encountered by households searching decent housing nearby workplaces, many experts argue that efficient urban policies promoting a diversified housing supply nearby job centres would allow more reasonable commuting distances and that such a return should go forth with a reduction in car traffic. In this paper, through a simulation model based on re-assignment of households closer to their workplaces, we examine the potential of car traffic reduction in the case of the Paris region. More precisely the impact of jobs-housing balance policy is based on a simulation model which states assignment of households located far from their work place within zones located nearer to the work place. The households that are reassigned are those where all workers travel more than a given time-threshold to reach their work place. These households are relocated within a perimeter around either the work place of the head of the household if it is a one worker household or the work place of the female worker if it is a two worker household - this perimeter is defined with reference to a time-threshold (set to 20, 30 or 45 minutes by private car or by public transport). For each type of household (defined according to social status, number of workers and family profile), the type of housing demanded by reassigned households is derived from the structure of housing detained by households that are already located within the perimeter of re-assignment. Three analyses are conducted on the basis of this simulation. According to the different time-thresholds : first, we estimate the total distances saved on home-work trips by private car when households are reassigned. Second, we identify the characteristics of reassigned households (especially social status, number of workers, family profile, residential location, job location, etc.). Third, we estimate the housing offer/demand imbalance after re-assignment (with specific interest for the case of housing for low-income groups).

Chronoamperometric study of the passive behaviour of tantalum in hostile media during water addition

The ability of tantalum to become passive through water addition in methanol solution during chronoamperometric experiments has been investigated. The achievement of passivity was found to be modulated according to the applied electrical potential and the nature of the aggressive anions. The chronoamperometric curves were interpreted as resulting from the balance between the influence of proton mobility in solution and the building of the passive film

Effect of ball milling in a tumbling ball mill on the properties of multi-wall carbon nanotubes

The effects of ball milling on various properties of ground multi-wall carbon nanotubes were studied. These properties were granulometry, SEM,specific surface area, density, crystalline structure, surface chemical analysis and thermogravimetry. The mean size of agglomerates, initially at 35 m, decreases to reach a limit value of 2.5m, corresponding to a competition between agglomeration and fragmentation. A kinetic study,based on a decomposition of size distributions measured for different times, has permitted to propose a grinding mechanism. As grinding proceeds, the specific surface area first increases from 175 to 244m2 g−1 and then decreases, while the real density increases from 1800 to 2150 kgm−3 to level off at 2070 kgm−3. Moreover, macroporosity disappears totally, giving access first to mesoporosity and then to microporosity. The nanotubes are probably cut to give access to the internal porosity. An increase of the proportion of oxygen adsorbed on carbon (from 3% to 8.7% after 600 min grinding) implies that it may be possible to functionalise the nanotubes. Thanks to these different morphological changes numerous applications of ground nanotubes can be considered. Moreover, the use of a tumbling ball mill allows a massive production of cut nanotubes

Chiral symmetry, Confinement and Nuclear Matter properties

We discuss the possible influence of fundamental QCD properties such as spontaneous chiral symmetry breaking and nucleon substructure on nuclear matter properties. We propose a chiral version of the relativistic $\sigma-\omega$ model in which the attractive background scalar field is associated with the chiral invariant field governing the radial fluctuations of the quark condensate. Nuclear matter stability is ensured once the scalar response of the nucleon depending on the quark confinement mechanism is properly incorporated. The needed parameters are estimated from lattice results and a satisfactory description of bulk properties follows, the only really free parameter being the $\omega NN$ coupling constant. Pion loops can be also incorporated to obtain in a consistent way the finite density chiral susceptibilities. A good description of the asymmetry energy is obtained once the full rho meson exchange and Fock terms are included.Comment: Lecture given by G. Chanfray at the Theoretical Nuclear Physics School, 8-17 may 2007, Les Houches, Franc

Preparation of tantalum carbide films by reaction of electrolytic carbon coating with the tantalum substrate

This article demonstrates that coatings of tantalum carbide can be obtained by electrodeposition of carbon in molten fluorides on a tantalum substrate as an alternative to the CVD process. The structural characteristics of the carbon deposited by the electrolytic route lead to a high reactivity of this element towards a tantalum cathode to produce tantalum carbide. Mutual reactivity was shown to be enhanced if tantalum plate is replaced by an electrodeposited layer of tantalum, where the fine microstructure provides a catalytic effec

On the maximum mass of hyperonic neutron stars

Chiral Lagrangian and quark-meson coupling models of hyperon matter are used to estimate the maximum mass of neutron stars. Our relativistic calculations include, for the first time, both Hartree and Fock contributions in a consistent manner. Being related to the underlying quark structure of baryons, these models are considered to be good candidates for describing the dense core of neutron stars. Taking account of the known experimental constraints at saturation density, the equations of state deduced from these relativistic approaches cannot sustain a neutron star with a mass larger than 1.6-1.66 $M_\odot$

Beyond pressureless gas dynamics: Quadrature-based velocity moment models

Following the seminal work of F. Bouchut on zero pressure gas dynamics which has been extensively used for gas particle-flows, the present contribution investigates quadrature-based velocity moments models for kinetic equations in the framework of the infinite Knudsen number limit, that is, for dilute clouds of small particles where the collision or coalescence probability asymptotically approaches zero. Such models define a hierarchy based on the number of moments and associated quadrature nodes, the first level of which leads to pressureless gas dynamics. We focus in particular on the four moment model where the flux closure is provided by a two-node quadrature in the velocity phase space and provide the right framework for studying both smooth and singular solutions. The link with both the kinetic underlying equation as well as with zero pressure gas dynamics is provided and we define the notion of measure solutions as well as the mathematical structure of the resulting system of four PDEs. We exhibit a family of entropies and entropy fluxes and define the notion of entropic solution. We study the Riemann problem and provide a series of entropic solutions in particular cases. This leads to a rigorous link with the possibility of the system of macroscopic PDEs to allow particle trajectory crossing (PTC) in the framework of smooth solutions. Generalized $\delta$-choc solutions resulting from Riemann problem are also investigated. Finally, using a kinetic scheme proposed in the literature without mathematical background in several areas, we validate such a numerical approach in the framework of both smooth and singular solutions.Comment: Submitted to Communication in Mathematical Science

On the Eulerian Large Eddy Simulation of disperse phase flows: an asymptotic preserving scheme for small Stokes number flows

In the present work, the Eulerian Large Eddy Simulation of dilute disperse phase flows is investigated. By highlighting the main advantages and drawbacks of the available approaches in the literature, a choice is made in terms of modelling: a Fokker-Planck-like filtered kinetic equation proposed by Zaichik et al. 2009 and a Kinetic-Based Moment Method (KBMM) based on a Gaussian closure for the NDF proposed by Vie et al. 2014. The resulting Euler-like system of equations is able to reproduce the dynamics of particles for small to moderate Stokes number flows, given a LES model for the gaseous phase, and is representative of the generic difficulties of such models. Indeed, it encounters strong constraints in terms of numerics in the small Stokes number limit, which can lead to a degeneracy of the accuracy of standard numerical methods. These constraints are: 1/as the resulting sound speed is inversely proportional to the Stokes number, it is highly CFL-constraining, and 2/the system tends to an advection-diffusion limit equation on the number density that has to be properly approximated by the designed scheme used for the whole range of Stokes numbers. Then, the present work proposes a numerical scheme that is able to handle both. Relying on the ideas introduced in a different context by Chalons et al. 2013: a Lagrange-Projection, a relaxation formulation and a HLLC scheme with source terms, we extend the approach to a singular flux as well as properly handle the energy equation. The final scheme is proven to be Asymptotic-Preserving on 1D cases comparing to either converged or analytical solutions and can easily be extended to multidimensional configurations, thus setting the path for realistic applications