Retrieval of phenological stages of onion fields during the first year of growth by means of C-band polarimetric SAR measurements

The phenological stages of onion fields in the first year of growth are estimated using polarimetric observables and single-polarization intensity channels. Experiments are undertaken on a time series of RADARSAT-2 C-band full-polarimetric synthetic aperture radar (SAR) images collected in 2009 over the Barrax region, Spain, where ground truth information about onion growth stages is provided by the European Space Agency (ESA)-funded agricultural bio/geophysical retrieval from frequent repeat pass SAR and optical imaging (AgriSAR) field campaign conducted in that area. The experimental results demonstrate that polarimetric entropy or copolar coherence when used jointly with the cross-polarized intensity allows unambiguously distinguishing three phenological intervals.

Influence of Incidence Angle on the Coherent Copolar Polarimetric Response of Rice at X-Band

The coherent nature of the acquisition by TerraSAR-X of both copolar channels (HH and VV) enables the generation of many different polarimetric observables with physical interpretation, as have recently been used for monitoring rice fields. In this letter, the influence of incidence angle upon these polarimetric observables is analyzed by comparing three stacks of images that were acquired simultaneously at different incidence angles (22°, 30°, and 40°) during a whole cultivation campaign. We show that the response of observables related to dominance (entropy, ratios of components) and type of scattering mechanisms (alpha angles) is not greatly influenced by incidence angle at some stages: early and advanced vegetative phases, and maturation. Moreover, the acquisition geometry drives the sensitivity to the presence of the initial stems and tillers, being detected earlier at shallower angles. This analysis is a necessary step before studying potential methodologies for combining different orbits and beams for reducing the time between acquisitions for monitoring purposes.

Simulated magnetic field expulsion in neutron star cores

The study of long-term evolution of neutron star (NS) magnetic fields is key to understanding the rich diversity of NS observations, and to unifying their nature despite the different emission mechanisms and observed properties. Such studies in principle permit a deeper understanding of the most important parameters driving their apparent variety, e.g. radio pulsars, magnetars, X-ray dim isolated NSs, gamma-ray pulsars. We describe, for the first time, the results from self-consistent magnetothermal simulations considering not only the effects of the Hall-driven field dissipation in the crust, but also adding a complete set of proposed driving forces in a superconducting core. We emphasize how each of these core-field processes drive magnetic evolution and affect observables, and show that when all forces are considered together in vectorial form, the net expulsion of core magnetic flux is negligible, and will have no observable effect in the crust (consequently in the observed surface emission) on megayear time-scales. Our new simulations suggest that strong magnetic fields in NS cores (and the signatures on the NS surface) will persist long after the crustal magnetic field has evolved and decayed, due to the weak combined effects of dissipation and expulsion in the stellar core.

Miscellanea curiosa : Containing a collection of some of the principal phaenomena in nature, accounted for by the greatest philosophers of this age; being the most valuable discourses, read and delivered to the Royal Society, for the advancement of physical and mathematical knowledge. As also a collection of curious travels, voyages, antiquities, and natural histories of countries; presented to the same society.

"A letter from Mr. John Clayton ... giving an account of several observables in Virginia, and in his voyage thither", v. 3, p. 281-355.

La producción novelística de la "generación ausente" en el contexto de las memorias del pasado reciente argentino (1973-1983)

Ansgar Nünning y Astrid Erll (2003; 2005) y Astrid Erll (2005) han desarrollado las relaciones entre memoria y literatura introduciendo los conceptos de "memoria en la literatura: puestas en escena", "memoria de la literatura I: topoi e intertextualidad", "memoria de la literatura II: canon e historia de la literatura" y "literatura como medio de la memoria colectiva". Adoptando esta cuádruple distinción, la presente tesis doctoral se propone dar cuenta de la producción narrativa de la auto denominada "generación ausente" -conformada por autores nacidos alrededor del año 1960-, que tuvo entre sus preocupaciones principales tematizar el decenio 1973-1983, eligiendo para hacerlo la forma novela. Algunos de los escritores del corpus son: Carlos Gamerro, Matilde Sánchez, Daniel Guebel, Luis Chitarroni, Alan Pauls, Sergio Chejfec, Miguel Vitagliano, Gustavo Nielsen, Juan Forn, Carlos E. Feiling, Sergio Bizzio, Daniel Link, Martín Kohan, Damián Tabarovsky, Marcelo Figueras, Rodrigo Fresán y Ricardo Strafacce. Al respecto, el primer capítulo de este trabajo está dedicado a debatir las diversas utilizaciones del concepto de "generación" en la sociología de la literatura argentina, concepto que, a partir de la década del ochenta cayera en general descrédito. En efecto: luego del triunfo de lo que Miguel Dalmaroni entiende como la "'operación Raymond Williams' en Punto de Vista", se privilegiaron los conceptos de "grupo cultural" o "formación" de Raymond Williams para pensar colectivos culturales frente al de "generación". En nuestro trabajo, redefinimos "generación" como "construcción identitaria" (Cf. Jureit/ Wildt 2005) y "categoría de memoria" (Cf. Weigel 2005), esto es: entendida siempre como un constructo y en clave memorial, y en las antípodas de las formulaciones de matriz biologicista o embebidas de un afán matemático cercanas a la primitiva definición del concepto dada por José Ortega y Gasset. En un contexto de publicación de sus primeras novelas donde las llamadas "narrativas sobre los años setenta" comienzan a proliferar y con un marco de "crisis del mercado editorial" (1976-1989) y "concentración y polarización de la industrial editorial" (1990- 2000), los escritores estudiados se proponen volver a narrar la última dictadura, cuando la literatura ya no llenaría -como sí lo habría hecho en 1980- "un vacío de discurso" (Cf. Sarlo 2006). Sobre dicho contexto de publicación y numerosos análisis de la "memoria en la literatura" y la "memoria de la literatura I" observables en las novelas reseñadas versan los capítulos dos y tres de la presente tesis. Una de las hipótesis fundamentales de nuestro trabajo es que los novelistas del corpus no sólo intervinieron en el campo literario en calidad de escritores, sino que fueron "críticos estrategas" (en el sentido de Walter Benjamin) y "productores culturales" (en el sentido de Raymond Williams). Así, fueron miembros del staff de diversas revistas literarias, empleados de sellos ya existentes y/ o fundadores de las llamadas "editoriales independientes" y "editoriales artesanales", firmantes de textos de intervención -tanto en la prensa como en las dos últimas "historias de la literatura argentina" dirigidas, respectivamente, por Noé Jitrik y David Viñas-, pero también autores únicos de ambiciosos ensayos interpretativos donde se propone una determinada política de la literatura (en términos de Jacques Rancière), o bien un nuevo "canon" argentino. Por lo mismo, el capítulo cuatro de la presente tesis reseña estas intervenciones y las pone en diálogo con, por un lado, la producción estrictamente literaria de los novelistas del corpus, y, por el otro, con los que hemos hipotetizado como "cuatro grandes ciclos de canonización" ocurridos a partir de 1985, una vez mitigada la angustia de las influencias suscitada por Jorge Luis Borges. El recorrido planteado en esta tesis doctoral permite arribar a la conclusión general de que los autores del corpus, a partir de una muy acertada lectura del estado del campo literario argentino de fines de la década del ochenta del siglo XX (momento de triunfo de la operación crítica que hiciera de Juan José Saer, Manuel Puig y Ricardo Piglia los tres "nombres del consenso"), lograron en tiempo récord revertir su lugar inicial de carencia. Lo hicieron percibiendo el lugar central que, tanto en términos de memoria colectiva como de "memoria en la literatura", "memoria de la literatura I" y "memoria de la literatura II" ostentaba el decenio 1973-1983, con un alto nivel de consciencia del potencial estratégico que tenía el comparecer como "generación ausente", y haciendo un uso deliberadamente ambiguo de la etiqueta de la "nueva narrativa", que continua circulando hasta el día de hoy como contraseña en nuestro alicaído mercado de libros

Optimal cloning for finite distributions of coherent states

We derive optimal cloning limits for finite Gaussian distributions of coherent states and describe techniques for achieving them. We discuss the relation of these limits to state estimation and the no-cloning limit in teleportation. A qualitatively different cloning limit is derived for a single-quadrature Gaussian quantum cloner.

Spin-charge conductance in nanoscale electronic devices

We introduce a spin-charge conductance matrix as a unifying concept underlying charge and spin transport within the framework of the Landauer-Buttiker conductance formula. It turns out that the spin-charge conductance matrix provides a natural and gauge covariant description for electron transport through nanoscale electronic devices. We demonstrate that the charge and spin conductances are gauge invariant observables which characterize transport phenomena arising from spin-dependent scattering. Tunnelling through a single magnetic atom is discussed to illustrate our theory.

Critical behavior of one-particle spectral weights in the transverse Ising model

We investigate the critical behavior of the spectral weight of a single quasiparticle, one of the key observables in experiment, for the particular case of the transverse Ising model. Series expansions are calculated for the linear chain and the square and simple cubic lattices. For the chain model, a conjectured exact result is discovered. For the square and simple cubic lattices, series analyses are used to estimate the critical exponents. The results agree with the general predictions of Sachdev [Quantum Phase Transitions (Cambridge University Press, Cambridge, England, 1999)].

Efficient -tensor determination and NH assignment of paramagnetic proteins

Anisotropic magnetic susceptibility tensors chi of paramagnetic metal ions are manifested in pseudocontact shifts, residual dipolar couplings, and other paramagnetic observables that present valuable long-range information for structure determinations of protein-ligand complexes. A program was developed for automatic determination of the chi-tensor anisotropy parameters and amide resonance assignments in proteins labeled with paramagnetic metal ions. The program requires knowledge of the three-dimensional structure of the protein, the backbone resonance assignments of the diamagnetic protein, and a pair of 2D N-15-HSQC or 3D HNCO spectra recorded with and without paramagnetic metal ion. It allows the determination of reliable chi-tensor anisotropy parameters from 2D spectra of uniformly N-15-labeled proteins of fairly high molecular weight. Examples are shown for the 185-residue N-terminal domain of the subunit epsilon from E. coli DNA polymerase III in complex with the subunit theta and La3+ in its diamagnetic and Dy3+, Tb3+, and Er3+ in its paramagnetic form.

On the construction of correlation functions for the integrable supersymmetric fermion models

We review the recent progress on the construction of the determinant representations of the correlation functions for the integrable supersymmetric fermion models. The factorizing F-matrices (or the so-called F-basis) play an important role in the construction. In the F-basis, the creation (and the annihilation) operators and the Bethe states of the integrable models are given in completely symmetric forms. This leads to the determinant representations of the scalar products of the Bethe states for the models. Based on the scalar products, the determinant representations of the correlation functions may be obtained. As an example, in this review, we give the determinant representations of the two-point correlation function for the U-q(gl(2 vertical bar 1)) (i.e. q-deformed) supersymmetric t-J model. The determinant representations are useful for analyzing physical properties of the integrable models in the thermodynamical limit.

Studies on Wilson loops, correlators and localization in supersymmetric quantum field theories

In this thesis we study at perturbative level correlation functions of Wilson loops (and local operators) and their relations to localization, integrability and other quantities of interest as the cusp anomalous dimension and the Bremsstrahlung function. First of all we consider a general class of 1/8 BPS Wilson loops and chiral primaries in N=4 Super Yang-Mills theory. We perform explicit two-loop computations, for some particular but still rather general configuration, that confirm the elegant results expected from localization procedure. We find notably full consistency with the multi-matrix model averages, obtained from 2D Yang-Mills theory on the sphere, when interacting diagrams do not cancel and contribute non-trivially to the final answer. We also discuss the near BPS expansion of the generalized cusp anomalous dimension with L units of R-charge. Integrability provides an exact solution, obtained by solving a general TBA equation in the appropriate limit: we propose here an alternative method based on supersymmetric localization. The basic idea is to relate the computation to the vacuum expectation value of certain 1/8 BPS Wilson loops with local operator insertions along the contour. Also these observables localize on a two-dimensional gauge theory on S^2, opening the possibility of exact calculations. As a test of our proposal, we reproduce the leading Luscher correction at weak coupling to the generalized cusp anomalous dimension. This result is also checked against a genuine Feynman diagram approach in N=4 super Yang-Mills theory. Finally we study the cusp anomalous dimension in N=6 ABJ(M) theory, identifying a scaling limit in which the ladder diagrams dominate. The resummation is encoded into a Bethe-Salpeter equation that is mapped to a Schroedinger problem, exactly solvable due to the surprising supersymmetry of the effective Hamiltonian. In the ABJ case the solution implies the diagonalization of the U(N) and U(M) building blocks, suggesting the existence of two independent cusp anomalous dimensions and an unexpected exponentation structure for the related Wilson loops.

Dynamics of learning with restricted training sets

The dynamics of supervised learning in layered neural networks were studied in the regime where the size of the training set is proportional to the number of inputs. The evolution of macroscopic observables, including the two relevant performance measures can be predicted by using the dynamical replica theory. Three approximation schemes aimed at eliminating the need to solve a functional saddle-point equation at each time step have been derived.

Statistical mechanics of low-density parity check error-correcting codes over Galois fields

A variation of low-density parity check (LDPC) error-correcting codes defined over Galois fields (GF(q)) is investigated using statistical physics. A code of this type is characterised by a sparse random parity check matrix composed of C non-zero elements per column. We examine the dependence of the code performance on the value of q, for finite and infinite C values, both in terms of the thermodynamical transition point and the practical decoding phase characterised by the existence of a unique (ferromagnetic) solution. We find different q-dependence in the cases of C = 2 and C ≥ 3; the analytical solutions are in agreement with simulation results, providing a quantitative measure to the improvement in performance obtained using non-binary alphabets.

Error-correcting codes on a Bethe-like lattice

We analyse Gallager codes by employing a simple mean-field approximation that distorts the model geometry and preserves important interactions between sites. The method naturally recovers the probability propagation decoding algorithm as a minimization of a proper free-energy. We find a thermodynamical phase transition that coincides with information theoretical upper-bounds and explain the practical code performance in terms of the free-energy landscape.

Statistical mechanics of low-density parity-check codes

We review recent theoretical progress on the statistical mechanics of error correcting codes, focusing on low-density parity-check (LDPC) codes in general, and on Gallager and MacKay-Neal codes in particular. By exploiting the relation between LDPC codes and Ising spin systems with multispin interactions, one can carry out a statistical mechanics based analysis that determines the practical and theoretical limitations of various code constructions, corresponding to dynamical and thermodynamical transitions, respectively, as well as the behaviour of error-exponents averaged over the corresponding code ensemble as a function of channel noise. We also contrast the results obtained using methods of statistical mechanics with those derived in the information theory literature, and show how these methods can be generalized to include other channel types and related communication problems.