On the invariant symmetries of the D\mathcal{D}-metrics

We analyze the symmetries and other invariant qualities of the $\mathcal{D}$-metrics (type D aligned Einstein Maxwell solutions with cosmological constant whose Debever null principal directions determine shear-free geodesic null congruences). We recover some properties and deduce new ones about their isometry group and about their quadratic first integrals of the geodesic equation, and we analyze when these invariant symmetries characterize the family of metrics. We show that the subfamily of the Kerr-NUT solutions are those admitting a Papapetrou field aligned with the Weyl tensor.Comment: 18 pages; v2: minor change

How Noisy Data Affects Geometric Semantic Genetic Programming

Noise is a consequence of acquiring and pre-processing data from the environment, and shows fluctuations from different sources---e.g., from sensors, signal processing technology or even human error. As a machine learning technique, Genetic Programming (GP) is not immune to this problem, which the field has frequently addressed. Recently, Geometric Semantic Genetic Programming (GSGP), a semantic-aware branch of GP, has shown robustness and high generalization capability. Researchers believe these characteristics may be associated with a lower sensibility to noisy data. However, there is no systematic study on this matter. This paper performs a deep analysis of the GSGP performance over the presence of noise. Using 15 synthetic datasets where noise can be controlled, we added different ratios of noise to the data and compared the results obtained with those of a canonical GP. The results show that, as we increase the percentage of noisy instances, the generalization performance degradation is more pronounced in GSGP than GP. However, in general, GSGP is more robust to noise than GP in the presence of up to 10% of noise, and presents no statistical difference for values higher than that in the test bed.Comment: 8 pages, In proceedings of Genetic and Evolutionary Computation Conference (GECCO 2017), Berlin, German

Estimating small angular scale CMB anisotropy with high resolution N-body simulations: weak lensing

We estimate the impact of weak lensing by strongly nonlinear cosmological structures on the cosmic microwave background. Accurate calculation of large $\ell$ multipoles requires N-body simulations and ray-tracing schemes with both high spatial and temporal resolution. To this end we have developed a new code that combines a gravitational Adaptive Particle-Particle, Particle-Mesh (AP3M) solver with a weak lensing evaluation routine. The lensing deviations are evaluated while structure evolves during the simulation so that all evolution steps--rather than just a few outputs--are used in the lensing computations. The new code also includes a ray-tracing procedure that avoids periodicity effects in a universe that is modeled as a 3-D torus in the standard way. Results from our new simulations are compared with previous ones based on Particle-Mesh simulations. We also systematically investigate the impact of box volume, resolution, and ray-tracing directions on the variance of the computed power spectra. We find that a box size of $512 h^{-1}$ Mpc is sufficient to provide a robust estimate of the weak lensing angular power spectrum in the $\ell$-interval (2,000--7,000). For a reaslistic cosmological model the power $[\ell(\ell+1)C_{\ell}/2\pi]^{1/2}$ takes on values of a few $\mu K$ in this interval, which suggests that a future detection is feasible and may explain the excess power at high $\ell$ in the BIMA and CBI observations.Comment: 49 pages, 13 figures, accepted for publication in Ap

Avant la lettre: Philip Perry, Reconversionist Aesthetics, and the Medieval Literary

Producción Científica“Medievalism,” in the words of Tom Shippey, is “the study of responses to the Middle Ages at all periods since a sense of the mediaeval began to develop.”1 Although a relatively recent area of study, it nevertheless has long roots, and over time many practitioners, some better known than others. Philip Mark Perry (d. 1774), the subject of this essay, came early to the field, only to leave it before his efforts could see print. Nevertheless, his exploration of medieval writings and writers deserves greater recognition. Here we hope to establish that Perry's largely unedited manuscripts, now in Spain and Scotland, offer evidence of an exceptional contribution to the early narrative of medievalism.Financiado por la Agencia Estatal de Investigación, proyecto I+D "Misiones y transmisiones: intercambios entre la Península Ibérica y las Islas Británicas en la época Moderna Extensa" Ref: PID2020-113516GB-I0

¿Un sistema educativo comprensivo?

Any good educational system tries to keep the maximum number of students in the educational system for as long as possible, where he or she will receive a quality education which will prepare him or her for higher education and the labour market. In other words, they fight for a comprehensive educational system. The LOMCE is going to achieve the complete opposite. We shall analyze this more deeply in the following paragraphs. Keywords: Vocational training, higher vocational training, educational method, scholar evaluation, exam, income test, scholar dropout, basic education, secondary education, postsecondary education, higher education, private school, public school.Ningún sistema educativo intenta mantener el máximo número de estudiantes en el sistema educativo durante el mayor tiempo posible, donde el o ella recibirá una educación de calidad la cual los preparará para la educación superior y el mercado laboral. En otras palabras, ellos luchan por un sistema educativo comprensivo. La LOMCE va a lograr todo lo contrario. Nosotros analizaremos esto más profundamente en los siguientes párrafos.ReiDoCrea. Departamento de Psicología Social. Universidad de Granada