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Peer Reviewe

Spin transport in dangling-bond wires on doped H-passivated Si(100)

New advances in single-atom manipulation are leading to the creation of atomic structures on H passivated Si surfaces with functionalities important for the development of atomic and molecular based technologies. We perform total-energy and electron-transport calculations to reveal the properties and understand the features of atomic wires crafted by H removal from the surface. The presence of dopants radically change the wire properties. Our calculations show that dopants have a tendency to approach the dangling-bond wires, and in these conditions, transport is enhanced and spin selective. These results have important implications in the development of atomic-scale spintronics showing that boron, and to a lesser extent phosphorous, convert the wires in high-quality spin filters.Comment: 11 pages, 4 figure

Structural and magnetic properties of FeMnx_x (x=x=1...6) chains supported on Cu2_2N / Cu (100)

Heterogeneous atomic magnetic chains are built by atom manipulation on a Cu$_2$N/Cu (100) substrate. Their magnetic properties are studied and rationalized by a combined scanning tunneling microscopy (STM) and density functional theory (DFT) work completed by model Hamiltonian studies. The chains are built using Fe and Mn atoms ontop of the Cu atoms along the N rows of the Cu$_2$N surface. Here, we present results for FeMn$_x$ ($x$=1...6) chains emphasizing the evolution of the geometrical, electronic, and magnetic properties with chain size. By fitting our results to a Heisenberg Hamiltonian we have studied the exchange-coupling matrix elements $J$ for different chains. For the shorter chains, $x \leq 2$, we have included spin-orbit effects in the DFT calculations, extracting the magnetic anisotropy energy. Our results are also fitted to a simple anisotropic spin Hamiltonian and we have extracted values for the longitudinal-anisotropy $D$ and transversal-anisotropy $E$ constants. These parameters together with the values for $J$ allow us to compute the magnetic excitation energies of the system and to compare them with the experimental data.Comment: 10 pages 8 figure

Monetary policy and the output gap

Para una adecuada conducción de la política monetaria en una economía pequeña y abierta como la colombiana, debe tenerse en cuenta tanto el trilema de la política monetaria, como el ancla nominal de la economía. En este contexto, el papel del banco central es el de decidir cuál es el ancla nominal para la economía. Sin embargo, existe simultáneamente una estrecha relación entre la política monetaria y la brecha del producto. El objetivo de este estudio es ilustrar esta dinámica a través de un modelo de política monetaria. Los resultados muestran la relación dinámica entre el comportamiento de la tasa de interés como función de la inflación subyacente y la brecha del producto. Una de las principales características de la solución es que la restricción de no negatividad sobre la tasa de interés es obligatoria para bajos niveles de brecha del producto y bajas tasas de inflaciónTo develops an adequate an monetary policy, in a small open economy like the Colombian, must take in to account, the Trilema of monetary policy and the nominal anchor of the economy, in this context, the central bank role is that the decide which is the nominal anchor to the economy, however exist simultaneously a close relationship between the monetary policy and the gross domestic product gap, the goal of this study is to illustrate this dynamic thought of an monetary policy model, the results show that the behavior of an optimal interest rate like a function of the subjacent inflation and the gross domestic product gap, one of the principal characteristics of the solutions is that the restrictions of no negativity over the interest rate is necessary to lowers levels of gross domestic product gap and lowers rates of inflatio

Naturalness of MSSM dark matter

There exists a vast literature examining the electroweak (EW) fine-tuning problem in supersymmetric scenarios, but little concerned with the dark matter (DM) one, which should be combined with the former. In this paper, we study this problem in an, as much as possible, exhaustive and rigorous way. We have considered the MSSM framework, assuming that the LSP is the lightest neutralino, $\chi_1^0$, and exploring the various possibilities for the mass and composition of $\chi_1^0$, as well as different mechanisms for annihilation of the DM particles in the early Universe (well-tempered neutralinos, funnels and co-annihilation scenarios). We also present a discussion about the statistical meaning of the fine-tuning and how it should be computed for the DM abundance, and combined with the EW fine-tuning. The results are very robust and model-independent and favour some scenarios (like the h-funnel when $M_{\chi_1^0}$ is not too close to $m_h/2$) with respect to others (such as the pure wino case). These features should be taken into account when one explores "natural SUSY" scenarios and their possible signatures at the LHC and in DM detection experiments.Comment: 28 pages, 18 figures. References added, matches JHEP published versio

Diseño e implementación de un sistema de segmentación de los juegos de casinos de acuerdo con su nivel de actividad

El sector al cual apunta nuestro proyecto es el sector de la industria del Juego, específicamente en el sistema de las máquinas tragamonedas, las cuales bajo la perspectiva de un modelo de minería de datos permita a los administradores obtener conclusiones a fin de aplicarlas en su modelo de negocios. Específicamente tratamos el negocio de la empresa Interecuador S.A. dedicada al negocio de explotación de máquinas tragamonedas en calle, en locales y en salas de juego y casinos. El negocio posee diversos productos que pueden ser catalogados bajo dos grandes categorías: Mesas y máquinas. Dentro de mesas abarca todos los juegos de azar basados en cartas que tienen la intervención humana, este tipo de productos es exclusivo de casinos. Dentro de máquinas existen múltiples variedades de marcas, modelos y juegos los cuales se utilizan tanto en el negocio de calle, locales, casinos y salas de juego. Dadas las diversas características de los mismos es necesaria la implementación de un método que nos permita explorar los datos y encontrar la mejor combinación de características de determinada máquina de manera que su implementación en determinado local basado en la estadística me garantice la mejor producción de la misma

Local flexibility market design for aggregators providing multiple flexibility services at distribution network level

This paper presents a general description of local flexibility markets as a market-based management mechanism for aggregators. The high penetration of distributed energy resources introduces new flexibility services like prosumer or community self-balancing, congestion management and time-of-use optimization. This work is focused on the flexibility framework to enable multiple participants to compete for selling or buying flexibility. In this framework, the aggregator acts as a local market operator and supervises flexibility transactions of the local energy community. Local market participation is voluntary. Potential flexibility stakeholders are the distribution system operator, the balance responsible party and end-users themselves. Flexibility is sold by means of loads, generators, storage units and electric vehicles. Finally, this paper presents needed interactions between all local market stakeholders, the corresponding inputs and outputs of local market operation algorithms from participants and a case study to highlight the application of the local flexibility market in three scenarios. The local market framework could postpone grid upgrades, reduce energy costs and increase distribution grids’ hosting capacity.Postprint (published version

Rashba and Dresselhaus Effects in Hybrid Organic-Inorganic Perovskites: From Basics to Devices

J.E. and C.K. thank R. Winkler for fruitful discussions. We gratefully acknowledge Prof. R.-G.Xiong for providing Bz2PbCl4 crystallographic data.International audienceWe use symmetry analysis, density functional theory calculations, and k·p modeling to scrutinize Rashba and Dresselhaus effects in hybrid organic-inorganic halide perovskites. These perovskites are at the center of a recent revolution in the field of photovoltaics but have also demonstrated potential for optoelectronic applications such as transistors and light emitters. Due to a large spin-orbit coupling of the most frequently used metals, they are also predicted to offer a promising avenue for spin-based applications. With an in-depth inspection of the electronic structures and bulk lattice symmetries of a variety of systems, we analyze the origin of the spin splitting in two- and three-dimensional hybrid perovskites. It is shown that low-dimensional nanostructures made of CH3NH3PbX3 (X = I, Br) lead to spin splittings that can be controlled by an applied electric field. These findings further open the door for a perovskite-based spintronics