Discutir lo digital

En diferentes momentos de la historia, la tecnología ha cambiado la manera cómo se diseña la arquitectura. En ese sentido, la computadora no es la excepción. Este texto es una introducción al tema de la relación inevitable entre lo digital y el diseño arquitectónico. Parte de esta relación ha sido enmarcada por la forma cómo la "tecnologia" y lo "nuevo" se imponen como valores per se. Aquí se cuestionan esos valores y se propone las condiciones para que sea posible discutir la relación entre la computadora y el diseño arquitectónico, precisamente ahora que en Costa Rica los medios académicos están incorporando programas de computación que abren paso a diferentes modos de diseñar y, sin duda también, de entender la arquitectura en el país.At different times in history, technology has changed the ways architects design. In this regard, the computer is no exception. This article generates an introductory discussion about the inevitable relationship between the digital and architectural design. Part of this relationship has been set out in a frame where "technology" and the "new" are seen as values per se. This text questions these values and suggests some of the conditions that could make a discussion possible on the computer and architectural design, precisely at a time when schools of architecture in Costa Rica are introducing soSware that is ushering in a difference in the way architecture is designed and understood in the country

Energy bands of atomic monolayers of various materials: Possibility of energy gap engineering

The mobility of graphene is very high because the quantum Hall effects can be observed even at room temperature. Graphene has the potential of the material for novel devices because of this high mobility. But the energy gap of graphene is zero, so graphene can not be applied to semiconductor devices such as transistors, LEDs, etc. In order to control the energy gaps, we propose atomic monolayers which consist of various materials besides carbon atoms. To examine the energy dispersions of atomic monolayers of various materials, we calculated the electronic states of these atomic monolayers using density functional theory with structural optimizations. The quantum chemical calculation software "Gaussian 03" was used under periodic boundary conditions. The calculation method is LSDA/6-311G(d,p), B3LYP/6-31G(d), or B3LYP/6-311G(d,p). The calculated materials are C (graphene), Si (silicene), Ge, SiC, GeC, GeSi, BN, BP, BAs, AlP, AlAs, GaP, and GaAs. These atomic monolayers can exist in the flat honeycomb shapes. The energy gaps of these atomic monolayers take various values. Ge is a semimetal; AlP, AlAs, GaP, and GaAs are indirect semiconductors; and others are direct semiconductors. We also calculated the change of energy dispersions accompanied by the substitution of the atoms. Our results suggest that the substitution of impurity atoms for monolayer materials can control the energy gaps of the atomic monolayers. We conclude that atomic monolayers of various materials have the potential for novel devices.Comment: This paper was first presented at the 14th International Conference on Modulated Semiconductor Structures (MSS14) held in Kobe, Japan, on 23 July 200

Landau Theory of Barocaloric Plastic Crystals

We present a simple Landau phenomenology for plastic-to-crystal phase transitions and use the resulting model to calculate barocaloric effects in plastic crystals that are driven by hydrostatic pressure. The essential ingredients of the model are (i) a multipole-moment order parameter that describes the orientational ordering of the constituent molecules, (ii) coupling between such order parameter and elastic strains, and (iii) the thermal expansion of the solid. The model captures main features of plastic-to-crystal phase transitions, namely large volume and entropy changes at the transition, and strong dependence of the transition temperature with pressure. Using solid C$_{60}$ under $0.60\,$GPa as case example, we show that calculated peak isothermal entropy changes of $\sim 58 \,{\rm J K^{-1} kg^{-1}}$ and peak adiabatic entropy changes of $\sim 23 \,{\rm K}$ agree well with experimental values.Comment: 17 pages, 3 figure

Electronic structure of silicon-based nanostructures

We have developed an unifying tight-binding Hamiltonian that can account for the electronic properties of recently proposed Si-based nanostructures, namely, Si graphene-like sheets and Si nanotubes. We considered the $sp^3s^*$ and $sp^{3}$ models up to first- and second-nearest neighbors, respectively. Our results show that the Si graphene-like sheets considered here are metals or zero-gap semiconductors, and that the corresponding Si nanotubes follow the so-called Hamada's rule [Phys. Rev. Lett. {\bf 68}, 1579 1992]. Comparison to a recent {\it ab initio} calculation is made.Comment: 12 pages, 6 Figure

Cielo, Ciudad y Acontecimiento

ResumenCon la tecnología del avión se estableció un cambio radical en nuestro sentido de la dirección y la distancia. Diferente a la ruta horizontal del tren, el avión instauró la ruta vertical, concebimos la experiencia de ascender y descender desde el cielo hacia el suelo y viceversa como algo normal en nuestras vidas. Sobre todo, con el avión se estableció una de las fantasías fundamentales del mundo moderno: al ver la ciudad desde arriba y desde la distancia, el pasajero-sujeto cree tener el poder para analizar, desde un punto de vista privilegiado, eso que está allá abajo, a lo lejos

Band structure of hydrogenated Si nanosheets and nanotubes

The band structure of fully hydrogenated Si nanosheets and nanotubes are elucidated by the use of an empirical tight-binding model. The hydrogenated Si sheet is a semiconductor with indirect band gap of about 2.2 eV. The symmetries of the wave functions allow us to explain the origin of the gap. We predict that, for certain chiralities, hydrogenated Si nanotubes represent a new type of semiconductor, one with co-existing direct and indirect gaps of exactly the same magnitude. This behavior is different from the Hamada rule established for non-hydrogenated carbon and silicon nanotubes. Comparison to an ab initio calculation is made.Comment: 9 pages, 4 figures, to appear in J. Phys.: Condens. Matte

A variational method in the problem of screening an external charge in strongly correlated metals

We describe a variational calculation for the problem of screening of a point charge in a layered correlated metal for dopings close to the Mott transition where the screening is non-linear due to the proximity to the incompressible insulating state. We find that external charge can induce locally incompressible regions and that the non-linear dependence of the screening on density can induce overscreening in the nearest nearby layers while preserving overall charge neutrality.Comment: 7 pages, 1 figure, final version as publishe

Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites

Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed

Landau theory and giant room-temperature barocaloric effect

The structural phase transitions of MF3 (M = Al, Cr, V, Fe, Ti, Sc) metal trifluorides are studied within a simple Landau theory consisting of tilts of rigid MF6 octahedra associated with soft antiferrodistortive optic modes that are coupled to long-wavelength strain generating acoustic phonons. We calculate the temperature and pressure dependence of several quantities such as the spontaneous distortions, volume expansion, and shear strains as well as T−P phase diagrams. By contrasting our model to experiments we quantify the deviations from mean-field behavior and find that the tilt fluctuations of the MF6 octahedra increase with metal cation size. We apply our model to predict giant barocaloric effects in Sc-substituted TiF3 of up to about 15JK−1kg−1 for modest hydrostatic compressions of 0.2GPa. The effect extends over a wide temperature range of over 140K (including room temperature) due to a large predicted rate, dTc/dP=723KGPa−1, which exceeds those of typical barocaloric materials. Our results suggest that open lattice frameworks such as the trifluorides are an attractive platform to search for giant barocaloric effects.Universidad de Costa Rica/[816-B5-22]/UCR/Costa RicaU.S. Department of Energy, Office of Basic Energy Sciences, Material Sciences and Engineering Division/[contract no. DE-AC02-06CH11357]//Estados UnidosUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencia e Ingeniería de Materiales (CICIMA