Behaviors and housing inertia are key factors in determining the consequences of a shock in transportation costs

This paper investigates the consequences of a sudden increase in transportation costs when households behaviors and buildings inertia are accounted for. A theoretical framework is proposed, capturing the interactions between behaviors, transportation costs and urban structure. It is found that changes in households consumption and housing choices reduce significantly the long-term adverse effects of a shock in transportation costs. Indeed, the shock translates, over the long-run, into a more concentrated housing that limits households utility losses and maintains landowners' income. But, because of buildings inertia, the shock leads first to a long transition, during which the adjustment is constrained by a suboptimal housing-supply structure. Then, households support larger losses than in the final stage, though lower than with no adjustment at all, and landowners experience a large decrease in their aggregate income and an important redistribution of wealth. Negative transitional effects grow as the shock becomes larger. Thus, behaviors and buildings inertia are key factors in determining the vulnerability to transportation price variability and to the introduction of climate policies. Our policy conclusions are that: (i) if a long-term increase in transportation costs is unavoidable because of climate change or resource scarcity, a smooth change, starting as early as possible, must be favored; and (ii) fast-growing cities of the developing world can reduce their future vulnerability to shocks in transportation costs through the implementation of policies that limit urban sprawl.City, Housing, Transportation

Compact or Spread-Out Cities: Urban Planning, Taxation, and the Vulnerability to Transportation Shocks

This paper shows that cities made more compact by transportation taxation are more robust than spread-out cities to shocks in transportation costs. Such a shock, indeed, entails negative transition effects that are caused by housing infrastructure inertia and are magnified in low-density cities. Distortions due to a transportation tax, however, have in absence of shock detrimental consequences that need to be accounted for. The range of beneficial tax levels can, therefore, be identified as a function of the possible magnitude of future shocks in transportation costs. These taxation levels, which can reach significant values, reduce city vulnerability and prevent lock-ins in under-optimal situations.Urban transportation, Housing, Inertia, Vulnerability, Transportation Taxation

APEX observations of supernova remnants - I. Non-stationary MHD-shocks in W44

Aims. The interaction of supernova remnants (SNRs) with molecular clouds gives rise to strong molecular emission in the far-IR and sub-mm wavelength regimes. The application of MHD shock models in the interpretation of this line emission can yield valuable information on the energetic and chemical impact of supernova remnants. Methods. New mapping observations with the APEX telescope in CO (3-2), (4-3), (6-5), (7-6) and 13CO (3-2) towards two regions in the supernova remnant W44 are presented. Integrated intensities are extracted on five different positions, corresponding to local maxima of CO emission. The integrated intensities are compared to the outputs of a grid of models, which combine an MHD shock code with a radiative transfer module based on the large velocity gradient approximation. Results. All extracted spectra show ambient and line-of-sight components as well as blue- and red-shifted wings indicating the presence of shocked gas. Basing the shock model fits only on the highest-lying transitions that unambiguously trace the shock-heated gas, we find that the observed CO line emission is compatible with non-stationary shocks and a pre-shock density of 10^4 cm-3. The ages of the modelled shocks scatter between values of \sim1000 and \sim3000 years. The shock velocities in W44F are found to lie between 20 and 25 km/s, while in W44E fast shocks (30-35 km/s) as well as slower shocks (\sim20 km/s) are compatible with the observed spectral line energy diagrams. The pre-shock magnetic field strength components perpendicular to the line of sight in both regions have values between 100 and 200 \muG. Our best-fitting models allow us to predict the full ladder of CO transitions, the shocked gas mass in one beam as well as the momentum- and energy injection.Comment: 20 pages, 13 figures, 13 tables, accepted for publication in Astronomy and Astrophysic

High SiO abundance in the HH212 protostellar jet

Previous SiO maps of the innermost regions of HH212 set strong constraints on the structure and origin of this jet. They rule out a fast wide-angle wind, and tentatively favor a magneto-centrifugal disk wind launched out to 0.6 AU. We aim to assess the SiO content at the base of the HH212 jet to set an independent constraint on the location of the jet launch zone with respect to the dust sublimation radius. We present the first sub-arcsecond (0"44x0"96) CO map of the HH212 jet base, obtained with the IRAM Plateau de Bure Interferometer. Combining this with previous SiO(5-4) data, we infer the CO(2-1) opacity and mass-flux in the high-velocity jet and arrive at a much tighter lower limit to the SiO abundance than possible from the (optically thick) SiO emission alone. Gas-phase SiO at high velocity contains at least 10% of the elemental silicon if the jet is dusty, and at least 40% if the jet is dust-free, if CO and SiO have similar excitation temperatures. Such a high SiO content is challenging for current chemical models of both dust-free winds and dusty interstellar shocks. Updated chemical models (equatorial dust-free winds, highly magnetized dusty shocks) and observations of higher J CO lines are required to elucidate the dust content and launch radius of the HH212 high-velocity jet.Comment: 4 pages, 2 figure

Molecular emission in regions of star formation

Recent observations show that young stars being formed eject matter at several tens of kilometers per second, in the form of jets and outflows that impact the matter whose collapse is at the origin of the formation of the star. The supersonic impact between this jet and the parent interstellar cloud of the star generates a shock front, in the form of a bow-shock, which propagates in the collapsing interstellar gas, and also an inverse shock that propagates along the jet itself. The structure of these shocks depends on their velocity as well as on the physical properties of the gas in which they propagate. Numerical MagnetoHydroDynamİGal (MHD) simulations of the propagation of such shocks are a way to model the molecular emission arising from these regions, and thus to constrain the physical and chemical properties of the gas in which these molecular lines are emitted. A large grid of shock models is ran, for different values of key parameters such as the shock velocity, the pre-shock density, the magnetic field, ad the shock age. The emission of molecular hydrogen (whose treatment is included inside the shock code) is studied first. Pure rotational and rovibrational excitation diagrams are built for each model, and compared to the available observations of the bipolar outflow L1157. These comparisons confirm the necessity to use non stationary models to be able to interpret the observed column densities of H(_2). The emission of other characteristic molecules in the shocked region is then studied. The radiation transfer is computed thanks to a program based on the LVG (Large Velocity Gradient) approximation. In the case of SiO, comparisons with observed integrated intensities in L1157 are done, independently from the molecular hydrogen results, with a good agreement for stationary shock models and under diverse assumptions regarding the initial repartition of silicon in the dust grains, and oxygen in the gas phase. An attempt to simultaneous fitting of SiO and H(_2) observational data is then done, that is their fit by a very same (non stationary) shock model, with encouraging results. To complete this study, CO emission is treated similarly as SiO, and studied over the whole models grid. CO is then added to the list of molecules whose production and emission can be modelled by the same shock model as H(_2) and SiO with a satisfying agreement, even if this addition does not yield further constrain on the shock and medium properties

Detection of Extremely Broad Water Emission from the molecular cloud interacting Supernova Remnant G349.7+0.2

We performed Herschel HIFI, PACS and SPIRE observations towards the molecular cloud interacting supernova remnant G349.7+0.2. An extremely broad emission line was detected at 557 GHz from the ground state transition 1_{10}-1_{01} of ortho-water. This water line can be separated into three velocity components with widths of 144, 27 and 4 km/s. The 144 km/s component is the broadest water line detected to date in the literature. This extremely broad line width shows importance of probing shock dynamics. PACS observations revealed 3 additional ortho-water lines, as well as numerous high-J carbon monoxide (CO) lines. No para-water lines were detected. The extremely broad water line is indicative of a high velocity shock, which is supported by the observed CO rotational diagram that was reproduced with a J-shock model with a density of 10^4 cm^{-3} and a shock velocity of 80 km/s. Two far-infrared fine-structure lines, [O~I] at 145 micron and [C~II] line at 157 micron, are also consistent with the high velocity J-shock model. The extremely broad water line could be simply from short-lived molecules that have not been destroyed in high velocity J-shocks; however, it may be from more complicated geometry such as high-velocity water bullets or a shell expanding in high velocity. We estimate the CO and H2O densities, column densities, and temperatures by comparison with RADEX and detailed shock models. Detection of Extremely Broad Water Emission from the molecular cloud interacting Supernova Remnant G349.7+0.

Heterogeneity, climate change and stability of international fiscal harmonization

This paper analyses harmonization on fuel taxes between two coalitions. Harmonization is considered as a tool to mitigate greenhouse gas emissions, and reduce environmental costs. Domestic fuel producers can sell abroad, and their profits influence national governments in the negotiations. If all countries are identical, harmonization is environmental friendly provided environmental marginal damages are high. It is also economically profitable, but may be unstable if one of the coalitions is small enough. In this case, however, financial transfers between coalitions can stabilize harmonization. Nevertheless, countries can be heterogeneous with respect to the existence of a domestic producer. Heterogeneity introduces a new instability: not only the size, but also the composition of coalitions matters. Furthermore, the level of environmental damages also influences the stability of harmonization. In this case, intra- and inter-coalition financial transfers are necessary but not sufficient to stabilize harmonization