Density of States for a Specified Correlation Function and the Energy Landscape

The degeneracy of two-phase disordered microstructures consistent with a specified correlation function is analyzed by mapping it to a ground-state degeneracy. We determine for the first time the associated density of states via a Monte Carlo algorithm. Our results are described in terms of the roughness of the energy landscape, defined on a hypercubic configuration space. The use of a Hamming distance in this space enables us to define a roughness metric, which is calculated from the correlation function alone and related quantitatively to the structural degeneracy. This relation is validated for a wide variety of disordered systems.Comment: Accepted for publication in Physical Review Letter

State legitimacy and famines in Sub-Saharan Africa

Political Economy of famines mainly focuses on political regimes to understand the role of institutions. In this paper, we investigate a broader concept, state legitimacy, and its role on one specific development outcome, famine management. State legitimacy refers to the political history of a country, meaning the embedding of state and society. Using a database of Sub-Saharan countries observed from 1980 to 2005, we use three empirical strategies: logit on famine occurrence, negative binomial regression and Arellano-Bond dynamic model on the number of years of famines. They all lead to the same results: there is room for a political economy of famine based on an analysis of state. State legitimacy prevents famines, controlling for shocks countries might go through, and controlling for the quality of government. The main contributions of this paper are first to consider the role of state legitimacy in the political economy of famines and second to apply the concept in an empirical analysis, using for the first time a state legitimacy variable

Condensation-Induced Decrease of Small-Angle X-ray Scattering Intensity in Gelling Silica Solutions

peer reviewedWe propose a mathematical modeling of the total SAXS intensity in silica sol-gel processes in terms of hydrolysis and condensation reactions, as well as of microsyneresis. The results are used to rationalize previously published SAXS data of TEOS solutions reacting with organically modified trialkoxysilanes. We notably show that the decrease in SAXS intensity reported for these samples at the end of gelation is a consequence of condensation reactions. The water released by the latter reactions contributes to reduce the electron density difference between the silica and the solvent phases of the gel

Ukrepi in storitve centra za socialno delo za zaščito dekleta z izkušnjo spolne zlorabe v družini

Small-angle scattering of X-rays (SAXS) or neutrons (SANS) is one of the few experimental methods that can in principle be used for the in situ study at the mesoscopic scale of physicochemical phenomena occurring inside nanoporous solids. However, the potential of the method is often limited by the lack of suitable data analysis methods to convert scattering data into real-space structural information. This is notably the case for most porous materials of practical interest, which exhibit a hierarchical structure with micro, meso, and macropores, with often a secondary material confined in the pores, such as in supported catalysts, as well as fuel-cell and battery materials. In the present paper, we propose a general analysis of X-ray scattering by this type of material. Assuming that each structural level is statistically independent from the others and has a distinct characteristic length scale, compact mathematical expressions are derived for the scattering of the entire hierarchical structure. The results are particularized to the SAXS analysis of SBA-15-ordered mesoporous silica loaded with copper nitrate as well as of supported catalysts obtained after heat treatment of that material. The SAXS data analysis shows that the nitrate fills both the micro- and mesopores of the material, while the metallic copper obtained after heat treatment is found only in the mesopores. Moreover, the mesoscopic-scale spatial distribution of the metal depends on the heat treatment, in line with earlier electron tomography studies. The main ideas underlying the SAXS data analysis were presented in a recent communication (Gommes Angew. Chem., Int. Ed. 2015, 54, 11804−11808). Here, we generalize the approach and provide a comprehensive discussion of how any level in a hierarchical structure contributes to its overall scattering pattern. The results, as well as the general modeling methodology, will be of interest to anyone interested in the quantitative analysis of small-angle scattering data of empty or loaded porous solids and more generally of any type of hierarchical material

Relevance of Spinodal Decomposition for Support Formation and Metal Dispersion in Cogelled Pd/SiO2 Catalysts

peer reviewedThe structure formation of cogelled Pd/SiO2 catalysts is followed in situ at the nanometer scale using timeresolved small-angle X-ray scattering (SAXS). The SAXS patterns are analyzed in terms of a reaction-induced spinodal decomposition that is responsible for the formation of the silica support and most likely for the metal dispersion as well. The results are discussed in the light of recent electron tomography characterizations of the catalysts. The latter technique reveals regularity in the metal dispersion, the origin of which is likely to be the very occurrence of a spinodal phase separation

A more thorough analysis of water rockets: Moist adiabats, transient flows, and inertial forces in a soda bottle

Although water rockets are widely used to illustrate first year physics principles, accurate measurements show that they outperform the usual textbook analysis at the beginning of the thrust phase. This paper gives a more thorough analysis of this problem. It is shown that the air expansion in the rocket is accompanied by water vapor condensation, which provides an extra thrust; the downward acceleration of water within the rocket also contributes to the thrust, an effect that is negligible in other types of rockets; the apparent gravity resulting from the acceleration of the rocket contributes as much to water ejection as does the pressure difference between the inside and outside of the rocket; and the water flow is transient, which precludes the use of Bernoulli’s equation. Although none of these effects is negligible, they mostly cancel each other, and the overall accuracy of the analysis is only marginally improved. There remains a difference between theory and experiment with water rockets

Multiscale image analysis of microcellular solids: application to hybrid silica xerogels

A general methodology is proposed to characterize microcellular solids, the structure of which consists of a three-dimensional network of filamentary structures. The analysis is based on transmission electron microscopy observation of the filaments individually and of their spatial arrangement. The micrographs are analyzed with greytone digital image analysis techniques, such as opening granulometry and correlation analysis. The methodology is applied to hybrid organic–inorganic low-density silica solids synthesized by the sol–gel method with an organically modified co-reactant. The quantitative impact of the coreactant on each structural level of the structure is assessed quantitatively