English summary

<span style="font-family: Times New Roman; font-size: small;"> </span><span style="font-family: Times New Roman; font-size: small;"> </span><p style="margin: 0cm 0cm 0pt; line-height: normal; tab-stops: 1.0cm;" class="MsoNormal"><span lang="EN-GB" style="font-family: &quot;Times New Roman&quot;,&quot;serif&quot;; font-size: 12pt; mso-ansi-language: EN-GB;"> </span></p><span style="font-family: Times New Roman; font-size: small;"> </span><span style="font-family: Times New Roman; font-size: small;"> </span

Multisource Self-calibration for Sensor Arrays

Calibration of a sensor array is more involved if the antennas have direction dependent gains and multiple calibrator sources are simultaneously present. We study this case for a sensor array with arbitrary geometry but identical elements, i.e. elements with the same direction dependent gain pattern. A weighted alternating least squares (WALS) algorithm is derived that iteratively solves for the direction independent complex gains of the array elements, their noise powers and their gains in the direction of the calibrator sources. An extension of the problem is the case where the apparent calibrator source locations are unknown, e.g., due to refractive propagation paths. For this case, the WALS method is supplemented with weighted subspace fitting (WSF) direction finding techniques. Using Monte Carlo simulations we demonstrate that both methods are asymptotically statistically efficient and converge within two iterations even in cases of low SNR.Comment: 11 pages, 8 figure

Fundamental Imaging Limits of Radio Telescope Arrays

The fidelity of radio astronomical images is generally assessed by practical experience, i.e. using rules of thumb, although some aspects and cases have been treated rigorously. In this paper we present a mathematical framework capable of describing the fundamental limits of radio astronomical imaging problems. Although the data model assumes a single snapshot observation, i.e. variations in time and frequency are not considered, this framework is sufficiently general to allow extension to synthesis observations. Using tools from statistical signal processing and linear algebra, we discuss the tractability of the imaging and deconvolution problem, the redistribution of noise in the map by the imaging and deconvolution process, the covariance of the image values due to propagation of calibration errors and thermal noise and the upper limit on the number of sources tractable by self calibration. The combination of covariance of the image values and the number of tractable sources determines the effective noise floor achievable in the imaging process. The effective noise provides a better figure of merit than dynamic range since it includes the spatial variations of the noise. Our results provide handles for improving the imaging performance by design of the array.Comment: 12 pages, 8 figure

Spatial, temporal and social dimensions of the landscape influenced by contemporary art

The framework of this paper identifies various areas affected by the contemporary art practice in cultural landscape. Artistic practice in the landscape introduces new experiences to spectators. The author of this research explores what kinds of places are created by the contemporary art and whether it contributes to making new places. The research examines the identifying process of some features in creating the approach of dynamic landscape, and is carried out in accordance with the methodology of analysis. An approach of critical spatial practice proposed by Jane Rendell is explored through understanding the trialectical thinking. The research incorporates three parts: the spatial, temporal and social being for understanding nexus between an artwork and its settings. Expression means of artworks are analyzed in making the spatial analysis and clarifying the main features of connection. Among other indicators, cognition, place conception, context, refuge, connections, experience and temporality have been studied profoundly to understand the factors possibly influencing the landscape change. Article in English. Šiuolaikinio meno įtaka kraštovaizdžio erdviniams, laiko ir socialiniams aspektams Santrauka.&nbsp;Staipsnyje pateikiamos įvairios kultūrinį kraštovaizdį palietusios šiuolaikinio meno sritys. Stebint su kraštovaizdžiu susijusią meno praktiką, įgyjama naujos patirties. Darbo autorė tyrinėja šiuolaikinio meno įtaką erdvėms kurti. Tyrimo metu taikant analizės metodą nustatytos tam tikros kuriamo požiūrio į dinamišką kraštovaizdį ypatybės. Jane Rendell pasiūlyta kritinė erdvinė praktika nagrinėjama per trialektinio mąstymo suvokimą. Siekiant suprasti meno kūrinių ir aplinkos santykį, tyrimas buvo atliekamas susiejant erdvės, laiko ir socialinį aspektus. Meno kūrinių raiškos priemonės analizuotos erdvinės analizės būdu, nustatytos pagrindinės kūrinio ir jį supančios aplinkos ryšio savybės. Be kitų rodiklių – gebėjimo pažinti, vietos sampratos, situacijos, prieglobsčio, ryšių, patirties, laikinumo – buvo išsamiai nagrinėjami galimi kraštovaizdžio kaitos veiksniai. Raktiniai žodžiai:&nbsp;kultūrinis kraštovaizdis; kritinė erdvinė praktika; sąryšis; dinamiškas kraštovaizdi

Radio Astronomical Image Formation using Constrained Least Squares and Krylov Subspaces

Image formation for radio astronomy can be defined as estimating the spatial power distribution of celestial sources over the sky, given an array of antennas. One of the challenges with image formation is that the problem becomes ill-posed as the number of pixels becomes large. The introduction of constraints that incorporate a-priori knowledge is crucial. In this paper we show that in addition to non-negativity, the magnitude of each pixel in an image is also bounded from above. Indeed, the classical "dirty image" is an upper bound, but a much tighter upper bound can be formed from the data using array processing techniques. This formulates image formation as a least squares optimization problem with inequality constraints. We propose to solve this constrained least squares problem using active set techniques, and the steps needed to implement it are described. It is shown that the least squares part of the problem can be efficiently implemented with Krylov subspace based techniques, where the structure of the problem allows massive parallelism and reduced storage needs. The performance of the algorithm is evaluated using simulations

La imagen de escritor de Raúl González Tuñón, de los años sesenta a los treinta: relaciones entre literatura y política

Este artículo busca analizar la imagen de escritor que los jóvenes de la nueva izquierda argentina de los años sesenta, nucleados en el grupo de poesía “El pan duro” y en la revista y empresa editorial “La rosa blindada”, construyen de Raúl González Tuñón como “maestro” y “poeta de la revolución”. El propósito es desentrañar el porqué de esta elección y los modos en que esta imagen es productiva tanto para el proyecto de legitimación de las prácticas de estos jóvenes como para las del mismo González Tuñón, quien, por esos años, retoma muchos de los caminos de su poesía inicial ligada a la vanguardia. En este sentido, el artículo indaga las modalidades que reviste este rescate de la figura de Tuñón, es decir, qué recortes y selecciones operan en la construcción de esa imagen; para, a partir de allí, repensar la práctica poética e intelectual tuñoneana desde los años 30 hasta los 60.Fil: Alle, María Fernanda. Universidad Nacional del Litoral. Facultad de Humanidades y Ciencias. Centro de Estudios Comparados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe; Argentin