Noncollinear exchange interaction in transition metal dichalcogenide edges

We study the Ruderman-Kittel-Kasuya-Yosida effective exchange interaction between magnetic impurities embedded on the edges of transition-metal dichalcogenide flakes, using a three-orbital tight-binding model. Electronic states lying midgap of the bulk structure have strong one-dimensional (1D) character, localized on the edges of the crystallite. This results in exchange interactions with $1/r$ (or slower) decay with distance $r$, similar to other 1D systems. Most interestingly, however, the strong spin-orbit interaction in these materials results in sizable non-collinear Dzyaloshinskii-Moriya interactions between impurities, comparable in size to the usual Ising and in-plane components. Varying the relevant Fermi energy by doping or gating may allow one to modulate the effective interactions, controlling the possible helical ground state configurations of multiple impurities.Comment: 5 pages and 4 figure

Extending invariant complex structures

We study the problem of extending a complex structure to a given Lie algebra g, which is firstly defined on an ideal h of g. We consider the next situations: h is either complex or it is totally real. The next question is to equip g with an additional structure, such as a (non)-definite metric or a symplectic structure and to ask either h is non-degenerate, isotropic, etc. with respect to this structure, by imposing a compatibility assumption. We show that this implies certain constraints on the algebraic structure of g. Constructive examples illustrating this situation are shown, in particular computations in dimension six are given.Comment: 22 pages, plus an Addendu

Three Recent Damaging Earthquakes in Mexico

Seismicity in Mexico is largely influenced by subduction earthquakes that originate along much of its Pacific Coast. These events have recurrently damaged Mexico City but other less frequent earthquakes produced by other sources and mechanisms also contribute to seismic hazard there and have damaged other important cities and towns. In this paper we review, from the point of view of geotechnical engineering, the effects of three of these less frequent events: the Manzanillo earthquake of Octobrer 9, 1995, the Tehuacán Earthquake of June 6, 1999 and the Tecomán Earthquake of January 21, 2003

Ground Movements in Mexico City During Recent Earthquakes

Acceleration records were obtained with a rather dense accelerographic array during three recent earthquakes in Mexico City. Following a purely observational approach, useful information about the nature and characteristics of seismic motions was derived from the analysis of these records. Broad regional studies indicate that the distribution of seismic motions in the city may be affected by directivity effects. From local site studies it is concluded that seismic movements at the base of the compressible clay deposits are fairly uniform and accelerograms recorded in vertical arrays suggest that soil strata in Mexico City respond to seismic movements according to established knowledge

Radiolysis of Nucleosides: Study of Sedimentary Microenvironment Models for the Protection of Bio-Organic Molecules on Early Earth

Nucleic acid bases and their derivatives are important compounds in biological systems. Many efforts have been made to demonstrate the possible prebiotic origin of these molecules, but the abiotic synthesis of these compounds has proved to be very difficult in that conditions. So, if their synthesis actually took place, a study of their stability in prebiotic conditions is quite relevant in chemical evolution studies. In this work, it has been examined and compared the influence of Sodium Montmorillonite on the chemical transformations undergone by two nucleosides (guanosine –purinic– and uridine, –pyrimidinic–) when subjected to conditions simulating the primitive Earth during the period of chemical evolution. The experiments prove the concentration capacity and protective role against external sources of ionizing radiation (specifically γ-ray) that clays can provide to these specific compounds adsorbed on them. By using X-ray diffraction, UV-vis spectrophotometry and HPLC for the analysis, it was found that purinic nucleosides (more than pyrimidinic) are quickly adsorbed on clay at low pH values, and the temperature of mineral desiccation applied after adsorption promotes their decomposition into their corresponding nitrogenous bases. In both, purinic and pyrimidinic, desorption occurs in neutral or slightly basic aqueous solutions, and both are protected by clay. Pyrimidinic nucleosides show more resistance to heat, but less resistance towards ionizing radiation, even when adsorbed in clay

Lateral Interfaces of Transition Metal Dichalcogenides: A Stable Tunable One-Dimensional Physics Platform

We study in-plane lateral heterostructures of commensurate transition-metal dichalcogenides, such as MoS$_{2}$-WS$_{2}$ and MoSe$_{2}$-WSe$_{2}$, and find interfacial and edge states that are highly localized to these regions of the heterostructure. These are one-dimensional (1D) in nature, lying within the bandgap of the bulk structure and exhibiting complex orbital and spin structure. We describe such heteroribbons with a three-orbital tight-binding model that uses first principles and experimental parameters as input, allowing us to model realistic systems. Analytical modeling for the 1D interfacial bands results in long-range hoppings due to the hybridization along the interface, with strong spin-orbit couplings. We further explore the Ruderman-Kittel-Kasuya-Yosida indirect interaction between magnetic impurities located at the interface. The unusual features of the interface states result in effective long-range exchange non-collinear interactions between impurities. These results suggest that transition-metal dichalcogenide interfaces could serve as stable, tunable 1D platform with unique properties for possible use in exploring Majorana fermions, plasma excitations and spintronics applications.Comment: 12 pages, 7 figure

A Simplified Elastic Model for Seismic Analysis of Earth-Retaining Structures with Limited Displacements

A simplified elastic model for analyzing static and dynamic interaction between earth-retaining structures and backfill within the range of small displacements is presented. The postulated model covers some of the available models as special cases. The model lends itself readily to the treatment of non-homogeneous backfills with elastic properties varying with depth. Internal (linear) damping in the backfill can be included without impairing the simplicity of the model. Radiation losses due to waves propagating horizontally in fills of semi-infinite extent are inherent to the postulated model. The solutions for some statical and dynamical problems of practical importance show satisfactory agreement with results based on the classical theory of elasticity