Le Corbusier: Architecture as a project of the world approach to a philosophy of architecture

La arquitectura moderna como un producto humano, ayudado por la técnica, da respuesta a las necesidades humanas en el proceso de habitar el mundo. El punto central es la revisión de un “proyecto de mundo” que para algunos maquinizó el problema del habitar y para otros apostó por la esencia antropológica que subyace a la necesidad de dar expresión material a un mejor mundo humano habitable. Este trabajo no procurará entonces hacer una “reivindicación” de Le Corbusier, pues a cada momento histórico le corresponden diversas respuestas a través de los productos humanos que dan cuenta de condiciones particulares de las culturas; se trata más bien de hacer una “reinterpretación” del proyecto de mundo que se gestó con el movimiento moderno de la arquitectura y, particularmente, con Le CorbusierThis article is a result of the reflection around the modern architecture as a human product than, supported by technical, gives answers to the human needs in the process of living in the world. The point is the search and reinterpretation of a “world project” that has been considered the “machining” of the world inhabit by some, and, for others, has been understood as a an movement that opted for the anthropological essence behind the need to give material expression to the human inhabit. This paper does not seek to make a “claim” to rescue Le Corbusier, as I am aware that each historical period has different answers by human products that account for conditions in the cultures, which clearly would not make sense to emulate; rather what I tried to make a “reinterpretation” of the proposed world was conceived with the modern movement in architecture and, particularly, with Le Corbusie

THz Magneto-electric atomic rotations in the chiral compound Ba3_3NbFe3_3Si2_2O14_{14}

We have determined the terahertz spectrum of the chiral langasite Ba$_3$NbFe$_3$Si$_2$O$_{14}$ by means of synchrotron-radiation measurements. Two excitations are revealed that are shown to have a different nature. The first one, purely magnetic, is observed at low temperature in the magnetically ordered phase and is assigned to a magnon. The second one persits far into the paramagnetic phase and exhibits both an electric and a magnetic activity at slightly different energies. This magnetoelectric excitation is interpreted in terms of atomic rotations and requires a helical electric polarization

Competing coexisting phases in 2D water

International audienceThe properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules

Structure et dynamique de la liaison hydrogène dans l'eau confinée ou aux interfaces

International audienceLorsque de l'eau est confinée dans une cavité nanométrique, ses propriétés structurales et dynamiques sont modifiées par rapport à celles de l'eau dans le volume. Les propriétés de l'eau confinée dans des oxydes présentent un intérêt à la fois fondamental et pratique, mais l'état du réseau percolatif dans ces cavités rigides est mal connu. Jusqu'à présent, la majorité des résultats a été obtenue sur de l'eau confinée dans de la matière molle. Nous présenterons ici des résultats obtenus sur la structure et la dynamique de l'eau confinée dans des systèmes rigides comme les oxydes. Pour cela, la spectroscopie infrarouge est une technique de choix, que ce soit par la grande gamme spectrale qu'elle offre (de l'infrarouge lointain, qui permet d'étudier des modes collectifs, au moyen infrarouge avec l'étude de la bande d'élongation O-H), mais aussi par la possibilité de faire des études de spectroscopie d'absorption transitoire femtoseconde qui donnent accès à la durée de vie du vibrateur O-H et à la rotation des molécules d'eau. Ces études ont été réalisées sur l'eau de surface (eau sur une surface d'alumine 1 ou à la surface d'un verre de silice 2 ,3) et l'eau confinée dans des géométries particulières, que ce soit un confinement tridimensionnel comme dans les pores de silice nanométrique 2 ou bidimensionnel comme dans les argiles 4. Les différences de comportement dynamique et de structure du réseau de liaisons hydrogène de l'eau confinée dans des systèmes « durs}) comme les oxydes ou « mous}) comme dans les échantillons biologiques (myoglobine concentrées ...) seront également discutées

Experimental and ab initio infrared study of χ-, κ- and α-aluminas formed from gibbsite

χ-, κ- and α-alumina phases formed by dehydration of micro-grained gibbsite between 773 and 1573 K are studied using infrared spectroscopy (IR). The structural transitions evidenced by X-ray diffraction (XRD) were interpreted by comparing IR measurements with ab initio simulations (except for the χ form whose complexity does not allow a reliable simulation). For each phase, IR spectrum presents specific bands corresponding to transverse optical (TO) modes of Al-O stretching and bending under 900 cm-1. The very complex χ phase, obtained at 773 K, provides a distinctive XRD pattern in contrast with the IR absorbance appearing as a broad structure extending between 200 and 900 cm-1 resembling the equivalent spectra for γ-alumina phase. κ-alumina is forming at 1173 K and its rich IR spectrum is in good qualitative agreement with ab initio simulations. This complexity reflects the large number of atoms in the κ-alumina unit cell and the wide range of internuclear distances as well as the various coordinances of both Al and O atoms. Ab initio simulations suggest that this form of transition alumina demonstrates a strong departure from the simple pattern observed for other transition alumina. At 1573 K, the stable α-Αl2Ο3 develops. Its IR spectra extends in a narrower energy range as compared to transition alumina and presents characteristics features similar to model α-Αl2Ο3{dot operator} Ab initio calculations show again a very good general agreement with the observed IR spectra for this phase. In addition, for both κ- and α-Αl2Ο3, extra modes, measured at high energy (above 790 cm-1 for κ and above 650 cm-1 for α), can originate from either remnant χ-alumina or from surface mode

Vibronic collapse of ordered quadrupolar ice in the pyrochore magnet Tb2+x_{2+x}Ti2−x_{2-x}O7+y_{7+y}

While the spin liquid state in the frustrated pyrochlore Tb$_{2+x}$Ti$_{2-x}$O$_{7+y}$ has been studied both experimentally and theoretically for more than two decades, no definite description of this unconventional state has been achieved. Using synchrotron based THz spectroscopy in combination with quantum numerical simulations, we highlight a significant link between two previously unrelated features: the existence of a quadrupolar order following an ice rule and the presence of strong magneto-elastic coupling in the form of hybridized Tb$^{3+}$ crystal-field and phonon modes. The magnitude of this so-called vibronic process, which involves quadrupolar degrees of freedom, is significantly dependent on small off-stoichiometry $x$ and favors all-in all-out like correlations between quadrupoles. This mechanism competes with the long range ordered quadrupolar ice, and for slightly different stoichiometry, is able to destabilize it.Comment: Main text: 7 pages, 3 figures ; Supplemental Material: 6 pages, 2 figure

Optical Properties of Superconducting Nd0.8Sr0.2NiO2 Nickelate

The intensive search for alternative non-cuprate high-transition-temperature ($T_c$) superconductors has taken a positive turn recently with the discovery of superconductivity in infinite layer nickelates. This discovery is expected to be the basis for disentangling the puzzle behind the physics of high $T_c$ in oxides. In the unsolved quest for the physical conditions necessary for inducing superconductivity, we report an optical study of a Nd$_{0.8}$Sr$_{0.2}$NiO$_2$ film measured using optical spectroscopy, at temperatures above and below the critical temperature $T_c\sim 13$ K. The normal-state electrodynamics of Nd$_{0.8}$Sr$_{0.2}$NiO$_2$, is described by the Drude model characterized by a scattering time just above $T_c$ ($\tau \sim 1.7\times 10^{-14}$ s) and a plasma frequency $\omega_p = 8500$ cm$^{-1}$ in combination with an absorption band in the Mid-Infrared (MIR) around $\omega_0 \sim 4000$ cm$^{-1}$. The MIR absorption indicates the presence of strong electronic correlation effect in the NiO$_2$ plane similarly to cuprates. Below $T_c$, a superconducting energy gap ($2\Delta$) of $\sim 3.2$ meV is extracted from the Terahertz reflectivity using the the Mattis-Bardeen model. From the Ferrel-Glover-Thinkam Rule applied to the real part of the optical conductivity, we also estimate a London penetration depth of about 490 nm, in agreement with a type-II superconductivity in Nd$_{0.8}$Sr$_{0.2}$NiO$_2$ Nickelate

Low-temperature stability and sensing performance of mid-infrared bloch surface waves on a one-dimensional photonic crystal

The growing need for new and reliable surface sensing methods is arousing interest in the electromagnetic excitations of ultrathin films, i.e., to generate electromagnetic field distributions that resonantly interact with the most significant quasi-particles of condensed matter. In such a context, Bloch surface waves turned out to be a valid alternative to surface plasmon polaritons to implement high-sensitivity sensors in the visible spectral range. Only in the last few years, however, has their use been extended to infrared wavelengths, which represent a powerful tool for detecting and recognizing molecular species and crystalline structures. In this work, we demonstrate, by means of high-resolution reflectivity measurements, that a one-dimensional photonic crystal can sustain Bloch surface waves in the infrared spectral range from room temperature down to 10 K. To the best of our knowledge, this is the first demonstration of infrared Bloch surface waves at cryogenic temperatures. Furthermore, by exploiting the enhancement of the surface state and the high brilliance of infrared synchrotron radiation, we demonstrate that the proposed BSW-based sensor has a sensitivity on the order of 2.9 cm–1 for each nanometer-thick ice layer grown on its surface below 150 K. In conclusion, we believe that Bloch surface wave-based sensors are a valid new class of surface mode-based sensors for applications in materials science