Thermo-poro-mechanical analysis of landslides: from creeping behaviour to catastrophic failure

The scope of the paper encompasses planar and compound sliding motions, which may exhibit creeping behaviour during a certain period but may evolve to a very rapid motion. Thermo-mechanical interactions, at the scale of the sliding surface, are accepted as a critical aspect to explain these motion phases and their relationship. The sliding kinetics and global equilibrium are described at a large scale and the evolving shearing strength at the sliding surface derives from the local analysis of the shearing band and its vicinity. Pore pressures, temperatures and related variables are calculated by resolving a set of balance equations. The paper describes the transition from creeping motions to a rapid event. Results are found in terms of dimensionless numbers. Calculation of the slide evolution requires special numerical techniques described in the paper. Band permeability is found to be the dominant property controlling the triggering of fast motions. The creeping stage and the eventual slide blow-up are intimately linked. This relationship is explored in the paper. The models presented can be readily used to back-analyse relevant case histories or, in principle, even to carry out predictive modelling, provided an adequate calibration is available for the material parameters

Mechanisms of gas transport in clay barriers

Los ensayos de flujo de gas sobre muestras saturadas e impermeables indican la formación de sendas preferenciales de circulación del gas. El artículo describe un procedimiento para integrar esas discontinuidades en una formulación general THM tal y como se desarrolla en el Programa de elementos finitos CODE_BRIGHT. Con esta técnica se ha reproducido el comportamiento observado en muestras ensayadas. Se consigue reproducir los máximos observados en la presión de inyección y en el flujo de descarga cuando se abre por primera vez un camino preferencial. El artículo discute también el papel de la heterogeneidad a pequeña escala en el flujo de gas. Se ha desarrollado un experimento computacional inspirado en la geometría, materiales de barrera y condiciones de contorno del ensayo a gran escala GMT, desarrollado en el Laboratorio de Grimsel. Todos los elementos de la discretización incluyen discontinuidades embebidas. El análisis muestra que la pequeña variabilidad de propiedades de la barrera facilita el desarrollo de caminos preferenciales al flujo de gas

Analysis of a spatial Lotka-Volterra model with a finite range predator-prey interaction

We perform an analysis of a recent spatial version of the classical Lotka-Volterra model, where a finite scale controls individuals' interaction. We study the behavior of the predator-prey dynamics in physical spaces higher than one, showing how spatial patterns can emerge for some values of the interaction range and of the diffusion parameter.Comment: 7 pages, 7 figure

A Brane World Perspective on the Cosmological Constant and the Hierarchy Problems

We elaborate on the recently proposed static brane world scenario, where the effective 4-D cosmological constant is exponentially small when parallel 3-branes are far apart. We extend this result to a compactified model with two positive tension branes. Besides an exponentially small effective 4-D cosmological constant, this model incorporates a Randall-Sundrum-like solution to the hierarchy problem. Furthermore, the exponential factors for the hierarchy problem and the cosmological constant problem obey an inequality that is satisfied in nature. This inequality implies that the cosmological constant problem can be explained if the hierarchy problem is understood. The basic idea generalizes to the multibrane world scenario. We discuss models with piecewise adjustable bulk cosmological constants (to be determined by the 5-dimensional Einstein equation), a key element of the scenario. We also discuss the global structure of this scenario and clarify the physical properties of the particle (Rindler) horizons that are present. Finally, we derive a 4-D effective theory in which all observers on all branes not separated by particle horizons measure the same Newton's constant and 4-D cosmological constant.Comment: revtex, 63 pages, 8 figures, one table, revised version, more discussions on the global structure, references adde

A review of the fossil record of turtles of the clade Pan-Carettochelys

Turtles of the total clade Pan-Carettochelys have a relatively poor fossil record that extends from the Early Cretaceous. The clade is only found in Asia during the Cretaceous, but spreads to Europe and North America during the Eocene. Neogene finds are restricted to Europe, Africa and Australia, whereas the only surviving species, Carettochelys insculpta, lives in New Guinea and the Northern Territories of Australia. The ecology of fossil pan-carettochelyids appears similar to that of the extant C. insculpta, although more primitive representatives were likely less adapted to brackish water. Current phylogenies only recognize three internested clades: Pan- Carettochelys, Carettochelyidae and Carettochelyinae. A taxonomic review of the group concludes that of 25 named taxa, 13 are nomina valida, 7 are nomina invalida, 3 are nomina dubia, and 2 are nomina nuda

The IMF in Starbursts

The history of the IMF in starburst regions is reviewed. The IMFs are no longer believed to be top-heavy, although some superstar clusters, whether in starburst regions or not, could be. General observations of the IMF are discussed to put the starburst results in perspective. Observed IMF variations seem to suggest that the IMF varies a little with environment in the sense that denser and more massive clusters produce more massive stars, and perhaps more brown dwarfs too, compared to intermediate mass stars.Comment: 8 pages, to be published in ``Starbursts: from 30 Doradus to Lyman Break Galaxies,'' held at Institute of Astronomy, Cambridge University, UK, September 6-10, 2004. Kluwer Academic Publishers, edited by Richard de Grijs and Rosa M. Gonzalez Delgad

Trends and outcome of neoadjuvant treatment for rectal cancer: A retrospective analysis and critical assessment of a 10-year prospective national registry on behalf of the Spanish Rectal Cancer Project

Introduction: Preoperative treatment and adequate surgery increase local control in rectal cancer. However, modalities and indications for neoadjuvant treatment may be controversial. Aim of this study was to assess the trends of preoperative treatment and outcomes in patients with rectal cancer included in the Rectal Cancer Registry of the Spanish Associations of Surgeons. Method: This is a STROBE-compliant retrospective analysis of a prospective database. All patients operated on with curative intention included in the Rectal Cancer Registry were included. Analyses were performed to compare the use of neoadjuvant/adjuvant treatment in three timeframes: I)2006–2009; II)2010–2013; III)2014–2017. Survival analyses were run for 3-year survival in timeframes I-II. Results: Out of 14, 391 patients, 8871 (61.6%) received neoadjuvant treatment. Long-course chemo/radiotherapy was the most used approach (79.9%), followed by short-course radiotherapy ± chemotherapy (7.6%). The use of neoadjuvant treatment for cancer of the upper third (15-11 cm) increased over time (31.5%vs 34.5%vs 38.6%, p = 0.0018). The complete regression rate slightly increased over time (15.6% vs 16% vs 18.5%; p = 0.0093); the proportion of patients with involved circumferential resection margins (CRM) went down from 8.2% to 7.3%and 5.5% (p = 0.0004). Neoadjuvant treatment significantly decreased positive CRM in lower third tumors (OR 0.71, 0.59–0.87, Cochrane-Mantel-Haenszel P = 0.0008). Most ypN0 patients also received adjuvant therapy. In MR-defined stage III patients, preoperative treatment was associated with significantly longer local-recurrence-free survival (p < 0.0001), and cancer-specific survival (p < 0.0001). The survival benefit was smaller in upper third cancers. Conclusion: There was an increasing trend and a potential overuse of neoadjuvant treatment in cancer of the upper rectum. Most ypN0 patients received postoperative treatment. Involvement of CRM in lower third tumors was reduced after neoadjuvant treatment. Stage III and MRcN + benefited the most

Miniband-related 1.4–1.8 μm luminescence of Ge/Si quantum dot superlattices

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm