Apropa't a la ciencia

Presentamos una propuesta didáctica que permite contextualizar la ciencia en la sociedad: el taller ¿Cómo será la ciencia del futuro? realizado durante la exposición “Apropa’t a la ciència”, realizada en el Palau Robert de Barcelona entre abril y junio del 2007. El taller promueve la creatividad y la reflexión sobre la actividad científica, así como el debate sobre la relación entre la ciencia y la sociedad, mediante la discusión de noticias que sean portada de periódico en el año 2060, creadas por grupos de estudiantes después de su visita a la exposición. Analizamos la percepción social de ciencia, la inclusión de aspectos sociales y los temas les resultan más atractivos a partir de sus producciones e ideas previas. Simultáneamente nos interesa indagar la existencia o no de diferencias atribuibles al género en las visiones del alumnado

Eigenvalue estimates for non-normal matrices and the zeros of random orthogonal polynomials on the unit circle

We prove that for any $n\times n$ matrix, $A$, and $z$ with $|z|\geq \|A\|$, we have that \|(z-A)^{-1}\|\leq\cot (\frac{\pi}{4n}) \dist (z, \spec(A))^{-1}. We apply this result to the study of random orthogonal polynomials on the unit circle.Comment: 27 page

A census of ρ\rho Oph candidate members from Gaia DR2

The Ophiuchus cloud complex is one of the best laboratories to study the earlier stages of the stellar and protoplanetary disc evolution. The wealth of accurate astrometric measurements contained in the Gaia Data Release 2 can be used to update the census of Ophiuchus member candidates. We seek to find potential new members of Ophiuchus and identify those surrounded by a circumstellar disc. We constructed a control sample composed of 188 bona fide Ophiuchus members. Using this sample as a reference we applied three different density-based machine learning clustering algorithms (DBSCAN, OPTICS, and HDBSCAN) to a sample drawn from the Gaia catalogue centred on the Ophiuchus cloud. The clustering analysis was applied in the five astrometric dimensions defined by the three-dimensional Cartesian space and the proper motions in right ascension and declination. The three clustering algorithms systematically identify a similar set of candidate members in a main cluster with astrometric properties consistent with those of the control sample. The increased flexibility of the OPTICS and HDBSCAN algorithms enable these methods to identify a secondary cluster. We constructed a common sample containing 391 member candidates including 166 new objects, which have not yet been discussed in the literature. By combining the Gaia data with 2MASS and WISE photometry, we built the spectral energy distributions from 0.5 to 22\microm for a subset of 48 objects and found a total of 41 discs, including 11 Class II and 1 Class III new discs. Density-based clustering algorithms are a promising tool to identify candidate members of star forming regions in large astrometric databases. If confirmed, the candidate members discussed in this work would represent an increment of roughly 40% of the current census of Ophiuchus.Comment: A&A, Accepted. Abridged abstrac

Fractional Moment Estimates for Random Unitary Operators

We consider unitary analogs of $d-$dimensional Anderson models on $l^2(\Z^d)$ defined by the product $U_\omega=D_\omega S$ where $S$ is a deterministic unitary and $D_\omega$ is a diagonal matrix of i.i.d. random phases. The operator $S$ is an absolutely continuous band matrix which depends on parameters controlling the size of its off-diagonal elements. We adapt the method of Aizenman-Molchanov to get exponential estimates on fractional moments of the matrix elements of $U_\omega(U_\omega -z)^{-1}$, provided the distribution of phases is absolutely continuous and the parameters correspond to small off-diagonal elements of $S$. Such estimates imply almost sure localization for $U_\omega$

Recurrence for discrete time unitary evolutions

We consider quantum dynamical systems specified by a unitary operator U and an initial state vector \phi. In each step the unitary is followed by a projective measurement checking whether the system has returned to the initial state. We call the system recurrent if this eventually happens with probability one. We show that recurrence is equivalent to the absence of an absolutely continuous part from the spectral measure of U with respect to \phi. We also show that in the recurrent case the expected first return time is an integer or infinite, for which we give a topological interpretation. A key role in our theory is played by the first arrival amplitudes, which turn out to be the (complex conjugated) Taylor coefficients of the Schur function of the spectral measure. On the one hand, this provides a direct dynamical interpretation of these coefficients; on the other hand it links our definition of first return times to a large body of mathematical literature.Comment: 27 pages, 5 figures, typos correcte

Effect of polymer emulsion of the bearing capacity of Aeolian sand under extreme confinement conditions

An experimental investigation, aimed at evaluating the improvement of Aeolian sand (from Saudi Arabia) when treated with low dosages of a vinyl acrylic (a polymer emulsion), is reported in this paper. Special attention is devoted to the influence of the lateral confinement, particularly in terms of compaction and bearing capacity (represented by CBR), for which a modification of the standard test has been developed trying to simulate extreme confinement conditions. Experimental results demonstrate that this kind of chemical stabilizers can be considered as a suitable alternative for these materials. The main modifications induced in the sand by this additive are highlighted and quantified by means of the modification achieved for different geotechnical properties as well as Scanning Electron Microscope (SEM) and Energy-Dispersive X-Ray Spectroscopy (EDX) analyses

Localization for Random Unitary Operators

We consider unitary analogs of $1-$dimensional Anderson models on $l^2(\Z)$ defined by the product $U_\omega=D_\omega S$ where $S$ is a deterministic unitary and $D_\omega$ is a diagonal matrix of i.i.d. random phases. The operator $S$ is an absolutely continuous band matrix which depends on a parameter controlling the size of its off-diagonal elements. We prove that the spectrum of $U_\omega$ is pure point almost surely for all values of the parameter of $S$. We provide similar results for unitary operators defined on $l^2(\N)$ together with an application to orthogonal polynomials on the unit circle. We get almost sure localization for polynomials characterized by Verblunski coefficients of constant modulus and correlated random phases

CMV matrices in random matrix theory and integrable systems: a survey

We present a survey of recent results concerning a remarkable class of unitary matrices, the CMV matrices. We are particularly interested in the role they play in the theory of random matrices and integrable systems. Throughout the paper we also emphasize the analogies and connections to Jacobi matrices.Comment: Based on a talk given at the Short Program on Random Matrices, Random Processes and Integrable Systems, CRM, Universite de Montreal, 200

Transversalitat i coeducació a l'àrea de Física i Química en l'ESO : la classificació dels elements químics

Amb esta comunicació es posa de manifest que a l'any 2009 encara cal eixir al pas de les visions deformades de la ciència que ofereixen gran part dels materials curriculars. Planteja una proposta didàctica per a - contribuir a llevar les visions deformades que, de la ciència té el nostre alumnat: descontextualitzada, individualista i elitista, empiro-inductivista i ateòrica, rígida, algorítmica i infalible, aproblemàtica i ahistòrica, exclusivament analítica, visió acumulativa i de creixement lineal (GIL PÉREZ, Daniel; et al 2001). - tenir una imatge menys distorsionada de la realitat relacionant la ciència amb la societat, la tecnologia i el medi ambient des de la perspectiva de gènere. - donar una imatge més ajustada de la ciència que la que presenten la majoria de llibres de text

Transversalitat i coeducació a l'àrea de Física i Química en l'ESO : la classificació dels elements químics

Amb esta comunicació es posa de manifest que a l’any 2009 encara cal eixir al pas de les visions deformades de la ciència que ofereixen gran part dels materials curriculars. Planteja una proposta didàctica per a - contribuir a llevar les visions deformades que, de la ciència té el nostre alumnat: descontextualitzada, individualista i elitista, empiro-inductivista i ateòrica, rígida, algorítmica i infalible, aproblemàtica i ahistòrica, exclusivament analítica, visió acumulativa i de creixement lineal (GIL PÉREZ, Daniel; et al 2001). - tenir una imatge menys distorsionada de la realitat relacionant la ciència amb la societat, la tecnologia i el medi ambient des de la perspectiva de gènere. - donar una imatge més ajustada de la ciència que la que presenten la majoria de llibres de text