"Cómo pintar el aire". Fundamentos científicos de la perspectiva atmosférica

La perspectiva aérea o atmosférica es juzgada por los pintores como parte esencial de la pintura, una vez establecidos los presupuestos geométricos de la representación naturalista mediante la perspectiva lineal. Leonardo da Vinci fue el primer autor en definir la perspectiva aérea o atmosférica, conocidos ya a través de L. B. Alberti los fundamentos geométricos de la perspectiva lineal en el tratado De Pictura (1435). Doscientos años después, tras la influyente publicación del Optics de Newton, contextualizadas bajo el espíritu racionalista del siglo XVIII, el artículo estudia las recomendaciones que desde la ciencia y los científicos (específicamente a través de tres figuras relevantes: Brook Taylor, J. H. Lambert y Gaspard Monge) se dan a los pintores con la pretensión de arbitrar una medición exacta del color, en confrontación con el tradicional empirismo del mundo artístico. Este tema puede considerarse un capítulo de gran interés en la larga historia de la pintura y la representación de los fenómenos atmosféricos, cuyos antecedentes teóricos tienen su inicio en el Débat sur le Coloris de la Académie Française del siglo XVII y sus resultados, conducirán hacia el nacimiento de la moderna Teoría del color, en respuesta a una cuestión tan compleja sobre cómo pintar el aire.

The conflict between realism and abstraction in the field of spanish art as an iteration of la "Querelle des Anciens et des Modernes"

Based on the analysis model favored by the study of the conditions in which the seventeenth century Querelle des Anciens et des Modernes took place, we examine the case of confrontation between realism and abstraction, which occurred in the context of Spanish art in the nineties of the twentieth century. Connections are established with other aesthetic conflicts which are considered part of a genealogy whose most explicit antecedent could be placed in the before mentioned complaint, such as the confrontation between realism and abstraction in the American art scene, which occurred in the fifties of the last century, and the more recent controversy on pluralism and the end of art.

Analysis of Receiver Algorithms for LTE SC-FDMA Based Uplink MIMO Systems

This letter derives mathematical expressions for the received signal-to-interference-plus-noise ratio (SINR) of uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. An improved frequency domain receiver algorithm is derived for the studied systems, and is shown to be significantly superior to the conventional linear MMSE based receiver in terms of SINR and bit error rate (BER) performance.

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX.

We report calculations of energy levels, radiative rates and electron impact excitation cross<br/>sections and rates for transitions in He-like Cl XVI, K XVIII, Ca XIX and Sc XX. The grasp<br/>(general-purpose relativistic atomic structure package) is adopted for calculating energy levels<br/>and radiative rates. To determine the collision strengths and subsequently the excitation rates,<br/>the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line<br/>strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of<br/>each ion. Collision strengths are averaged over a Maxwellian velocity distribution and the<br/>effective collision strengths obtained listed over a wide temperature range up to 107.4 K.<br/>Comparisons are made with similar data obtained from the flexible atomic code (fac) to<br/>highlight the importance of resonances, included in calculations with darc, in the<br/>determination of effective collision strengths. Discrepancies between the collision strengths<br/>from darc and fac, particularly for forbidden transitions, are also discussed. Additionally,<br/>theoretical lifetimes are listed for all the 49 levels of the above four ions.

Electron-impact excitation of Sc II: collision strengths and effective collision strengths for fine-structure transitions.

Accurate fine-structure atomic data for the Fe-peak elements are essential for interpreting astronomical spectra. There is a severe paucity of data available for Sc II, highlighted by the fact that no collision strengths are readily available for this ion. We present electron-impact excitation collision strengths and Maxwellian averaged effective collision strengths for Sc II. The collision strengths were calculated for all 3916 transitions amongst 89 jj levels (arising from the 3d4s, 3d2, 4s2, 3d4p, 4s4p, 3d5s, 3d4d, 3d5p, 4p2 and 3d4f configurations), resulting in a 944 coupled channel problem. The R-matrix package RMATRXII was utilized, along with the transformation code FINE and the external region code PSTGF, to calculate the collision strengths for a range of incident electron energies in the 0 to 8.3 Rydberg region. Maxwellian averaged effective collision strengths were then produced for 27 temperatures lying within the astrophysically significant range of 30 to 105 K.<br/>The collision strengths and effective collision strengths were produced for two different target models. The purpose was to systematically examine the effect of including open 3p correlation terms into the configuration interaction expansion for the wavefunction. The first model consisted of all 36 CI terms that could be generated with the 3p core closed. The second model incorporated an additional six configurations which allowed for single-electron excitations from within the 3p core. Comparisons are made between the two models and the results of Bautista et al., obtained by private communication. It is concluded that the first model produced the most reliable set of collision and effective collision strengths for use in astrophysical and plasma applications.

Electron-impact excitation of the astrophysically important singly ionized Fe-peak ions Sc and Ti

<p>In this work we report on the evaluation of electron-impact collision strengths and Maxwellian averaged effective collision strengths for the lowly-ionized Fe-peak elements Sc II and Ti II using the parallel R-matrix package RMATRX II.</p>

Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ti XXI, v XXII, Cr XXIII and Mn XXIV

<p>We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ti XXI, V XXII, Cr XXIII and Mn XXIV. grasp (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths and subsequently the excitation rates, the Dirac atomic R-matrix code (darc) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are listed for all the 49 levels of the above four ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 10 ^7.5K. Comparisons are made with similar data obtained using the flexible atomic code (fac) to highlight the importance of resonances, included in calculations with darc, in the determination of effective collision strengths. Discrepancies between the collision strengths from darc and fac, in particular for forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the darc code and earlier semi-relativistic R-matrix data are noted over a wide range of electron temperatures for many transitions in all ions. </p>