On the chemical composition of Titan’s dry lakebed evaporites

Titan, the main satellite of Saturn, has an active cycle of methane in its troposphere. Among other evidence for a mechanism of evaporation at work on the ground, dry lakebeds have been discovered. Recent Cassini infrared observations of these empty lakes have revealed a surface composition poor in water ice compared to that of the surrounding terrains—suggesting the existence of organic evaporites deposits. The chemical composition of these possible evaporites is unknown. In this paper, we study evaporite composition using a model that treats both organic solids dissolution and solvent evaporation. Our results suggest the possibility of large abundances of butane and acetylene in the lake evaporites. However, due to uncertainties of the employed theory, these determinations have to be confirmed by laboratory experiments.     

Digital complex correlator for a C-band polarimetry survey

The international Galactic Emission Mapping project aims to map and characterize the polarization field of the Milky Way. In Portugal it will map the sky polarized emission of the Northern Hemisphere in C-band and provide templates for map calibration and foreground control of microwave space data to be provided by ESA Planck Surveyor mission and later missions. The receiver system is equipped with a novel receiver with a full digital back-end using a low-cost Field Programmable Gate Array without compromising its performance relation. This new digital backend comprises a base-band complex cross-correlator outputting the four Stokes parameters of the incoming polarized radiation. In this document we describe the design and implementation of the complex correlator using the FPGA and the dedicated digitizers at each receiver arm, detailing the method applied at the several algorithm stages. This correlator is suitable for large sky area polarization continuum surveys.     

Technical guidelines for the assessment of earthquake induced liquefaction hazard at urban scale

Bulletin of Earthquake Engineering - Microzonation for earthquake-induced liquefaction hazard is the subdivision of a territory at a municipal or submunicipal scale in areas characterized by the...     

Site classification using equivalent soil profiles for building-liquefaction interaction

The seismic behaviour of a building on a liquefiable deposit is a complex interaction which involves quantifying both shaking induced damage and permanent ground deformation-related damage. In this paper the key parameters that influence both surface shaking and foundation settlements have been identified as the depth, thickness and liquefaction resistance of an equivalent liquefiable layer. These parameters can be used to develop an ‘equivalent soil profile’ that is analogous to the equivalent single degree-of-freedom that reduces the complexity of the dynamic response of a building into comparable and easily understood quantities. The equivalent soil profile is quantified independent of the seismic hazard, making it compatible with performance based design and assessment frameworks such that the building and soil profile can be directly assessed at different levels of seismic hazard. Several numerical studies are presented that demonstrate the influence of these key parameters on the ground surface shaking and foundation settlement. A set of criteria are proposed for classifying soil profiles into 22 different soil classes for regional loss assessment. An algorithm was developed for automatically fitting the equivalent soil profile to a cone penetration test trace and issues with the fitting are discussed. Field reconnaissance was undertaken to collect additional data to support existing datasets on the performance of buildings in Adapazari, during the 1999 Kocaeli, Turkey, earthquake (Mw = 7.4). The field case history data was used to investigate the correlation between the depth, thickness and liquefaction resistance of an equivalent liquefiable layer, on the extent of foundation permanent deformation. The case history data showed that in general a shallow, thick and weak liquefiable layer near the surface results in significant settlement but a lack of data for buildings on non-liquefiable deposits and the additional complexities involved with real buildings and soil deposits, meant that the trends observed in the idealised numerical models could not identified in the field case history data set.

     

Periodic motions in a gravitational central field with a rotating external force

We consider a Kepler problem, with an additional rotating external force, and study the existence of periodic solutions when a small perturbative term is introduced. Surprisingly enough, we always get at least one of such solutions. Moreover, if a nonresonance assumption is added, then the existence of a second solution is also proved.     

Estimating the Vehicle‐Miles‐Traveled Implications of Alternative Metropolitan Growth Scenarios: A Boston Example

This study demonstrates the potential value, and difficulties, in utilizing large‐scale, location aware, administrative data together with urban modeling to address current policy issues in a timely fashion. We take advantage of a unique dataset of millions of odometer readings from annual safety inspections of all private passenger vehicles in Metropolitan Boston to estimate the vehicle‐miles‐traveled (VMT) implication of alternative metropolitan growth scenarios: a sprawl‐type “let‐it‐be” scenario and a smart‐growth‐type “winds‐of‐change” scenario. The data are georeferenced to 250 × 250 m grid cells developed by MassGIS. We apply a greedy algorithm to assign Traffic Analysis Zone (TAZ) level household growth projections to grid cells and then use spatial interpolation tools to estimate VMT‐per‐vehicle surfaces for the region. If new growth households have similar VMT behavior as their neighbors, then the let‐it‐be scenario will generate 12–15% more VMT per household compared to the winds‐of‐change scenario. However, even the “wind‐of‐change” scenario, will result in new households averaging higher VMT per household than the Metro Boston average observed in 2005. The implication is that urban growth management can significantly reduce GHG but, by itself, will not be sufficient to achieve the GHG emission reduction targets set by the State for the transportation sector.     

Empirical assessment of flood wave celerity–discharge relationships at local and reach scales

ABSTRACT

An accurate comprehension of celerity (flood wave speed) dynamics is a key step for understanding flood wave propagation in rivers. We present the results of empirically estimated celerity values in 12 Brazilian rivers, and analyse the behaviour of celerity–discharge relationships (CxQ). Celerity was estimated with a reach-scale (RS) method, based on the peak travel time between stations; and with a local-scale (LS) method, based on the derivative of discharge–cross-section area relationships surveyed at gauging stations. The results indicate that the magnitudes of celerity values obtained by the methods are reasonably comparable, and can rarely be considered constant, varying with river discharge. Three reaches presented differing CxQ relationships at local and reach scales, which suggests that in situ cross-sections at gauging stations should not be extrapolated as representative of the whole reach for flood routing studies, and that CxQ relationship assessments might provide relevant insights for hydrological modelling.     

Discussion on the article “Paleoseismological analysis of an intraplate extensional structure: the Concud fault (Iberian Chain,Eastern Spain)” by P. Lafuente,L. E. Arlegui,C. L. Liesa,and J. L. Simón (Int J Earth Sci)

This discussion is focused on three aspects of the paper published by Lafuente et al. (Int J Earth Sci, doi: 10.1007/s00531-010-0542-1, 2010) on Concud Fault, constitute the fundamental basis to assess the seismic potential of this capable structure: (1) A slip rate estimated for the Concud Fault based on an erroneous displacement value and a questionable correlation, obviating previously published datings, markedly different to those used by the authors. The wrong displacement value introduces an error of more than 25% in the calculated Quaternary slip rate. (2) A new paleoseismological interpretation of the outcrop of Condud Fault at Los Baños, adding two improperly justified paleoearthquakes to the four events previously inferred. (3) The attribution of faults affecting a young terrace to the most recent recorded earthquake on Concud Fault, ruling out implicitly the likely option of a gravitational origin for them, either landsliding or subsidence due to evaporite dissolution.