Themed issue on selected papers SEG2015: part II

This themed issue of Geomechanics for Energy and the Environment ‘SEG-2015-Part II’, presents papers selected from extended abstracts submitted to the Symposium on Energy Geotechnics (SEG-2015) held in the Civil Engineering School of the Universitat Politècnica de Catalunya in Barcelona, Spain, between June 2nd and 4th, 2015. This symposium SEG-2015 was the first event organized by the Technical Committee TC308 of the International Society for Soil Mechanics and Geotechnical Engineering, which will have continuity in the next symposium SEG-2018 to be held in the École Polytechnique Fédérale de Lausanne (Lausanne, Switzerland). The first issue ‘SEG-2015-Part I’ appeared just before the 1st International Conference on Energy Geotechnics (ICEG-2016), which was held in Kiel (Germany) at the end of August 2016. The second volume ‘SEG-2015-Part II’ on December 2016 will thus close a first cycle of successful conferences and publications along this initial stage of TC308.Peer ReviewedPostprint (author's final draft

Yielding of rockfill in relative humidity-controlled triaxial experiments

The final publication is available at Springer via http://dx.doi.org/10.1007/s11440-016-0437-9The paper reports the results of suction controlled triaxial tests performed on compacted samples of two well graded granular materials in the range of coarse sand-medium gravel particle sizes: a quartzitic slate and a hard limestone. The evolution of grain size distributions is discussed. Dilatancy rules were investigated. Dilatancy could be described in terms of stress ratio, plastic work input and average confining stress. The shape of the yield locus in a triaxial plane was established by different experimental techniques. Yielding loci in both types of lithology is well represented by approximate elliptic shapes whose major axis follows approximately the Ko line. Relative humidity was found to affect in a significant way the evolution of grain size distribution, the deviatoric stress-strain response and the dilatancy rules.Peer ReviewedPostprint (author's final draft

Tricritical wedge filling transitions with short-ranged forces

We show that the 3D wedge filling transition in the presence of short-ranged interactions can be first-order or second order depending on the strength of the line tension associated with to the wedge bottom. This fact implies the existence of a tricritical point characterized by a short-distance expansion which differs from the usual continuous filling transition. Our analysis is based on an effective one-dimensional model for the 3D wedge filling which arises from the identification of the breather modes as the only relevant interfacial fluctuations. From such analysis we find a correspondence between continuous 3D filling at bulk coexistence and 2D wetting transitions with random-bond disorder.Comment: 7 pages, 3 figures, 6th Liquid Matter Conference Proceedings (to be published in J. Phys.: Condens. Matter

Renormalisation group determination of the order of the DNA denaturation transition

We report on the nature of the thermal denaturation transition of homogeneous DNA as determined from a renormalisation group analysis of the Peyrard-Bishop-Dauxois model. Our approach is based on an analogy with the phenomenon of critical wetting that goes further than previous qualitative comparisons, and shows that the transition is continuous for the average base-pair separation. However, since the range of universal critical behaviour appears to be very narrow, numerically observed denaturation transitions may look first-order, as it has been reported in the literature.Comment: 6 pages; no figures; to appear in Europhysics Letter

The (impossible?) formation of acetaldehyde on the grain surfaces: insights from quantum chemical calculations

Complex Organic Molecules (COMs) have been detected in the interstellar medium (ISM). However, it is not clear whether their synthesis occurs on the icy surfaces of interstellar grains or via a series of gas-phase reactions. As a test case of the COMs synthesis in the ISM, we present new quantum chemical calculations on the formation of acetaldehyde (CH3CHO) from the coupling of the HCO and CH3 radicals, both in gas phase and on water ice surfaces. The binding energies of HCO and CH3 on the amorphous water ice were also computed (2333 and 734 K, respectively). Results indicate that, in gas phase, the products could be either CH3CHO, CH4 + CO, or CH3OCH, depending on the relative orientation of the two radicals. However, on the amorphous water ice, only the CH4 + CO product is possible due to the geometrical constraints imposed by the water ice surface. Therefore, acetaldehyde cannot be synthesized by the CH3 + HCO coupling on the icy grains. We discuss the implications of these results and other cases, such as ethylene glycol and dimethyl ether, in which similar situations can occur, suggesting that formation of these molecules on the grain surfaces might be unlikely

Ice formation in unsaturated frozen soils

This paper presents a procedure for determining unfrozen water saturation in a partially saturated frozen soil (clayey silt) using bulk electrical conductivity (EC) measurements. A modification of Archie’s law is proposed to describe the relationship between soil bulk EC, temperature, porosity and degree of unfrozen water saturation. Compacted samples have been prepared at a dry density around 1.90 Mg/m3 and at dif-ferent degrees of saturation. Samples have been then subjected to freezing paths up to -15 °C. Measurements of bulk EC along the temperature decrease and freezing paths have been used to calibrate parameters associ-ated with the proposed model. These calibrated models allow determining the amount of ice content for a given state of the partially saturated soil (porosity, initial degree of water saturation and temperature). The soil freezing retention curve has been also estimated by combining the Clausius-Clapeyron equation with water retention data on drying. A good agreement has been observed between the estimation based on EC measurements and results from water retention data, which validates the proposed procedure.Postprint (published version

Function approximation in Hilbert spaces: a general sequential method and a particular implementation with neural networks

A sequential method for approximating vectors in Hilbert spaces, called Sequential Approximation with Optimal Coefficients (SAOC), is presented. Most of the existing sequential methods choose the new term so that it matches the previous residue as best as possible. Although this strategy leads to approximations convergent towards the target function, it may be far from being the best strategy with regard to the number of terms of the approximation. SAOC combines two key ideas. The first is the optimization of the coefficients (the linear part of the approximation). The second is the flexibility to choose the frequencies (the nonlinear part). The only relation with the residue has to do with its approximation capability of the target vector $f$. SAOC maintains orthogonal-like properties. The theoretical results obtained proof that, under reasonable conditions, the construction of the approximation is always possible and, in the limit, the residue of the approximation obtained with SAOC is the best one that can be obtained with any subset of the given set of vectors. In addition, it seems that it should achieve the same accuracy that other existent sequential methods with fewer terms. In the particular case of $L^2$, it can be applied to polynomials, Fourier series, wavelets and neural networks, among others. Also, a particular implementation using neural networks is presented. In fact, the profit is reciprocal, because SAOC can be used as an inspiration to construct and train a neural network.Postprint (published version