Casimir Effect and Global Theory of Boundary Conditions

The consistency of quantum field theories defined on domains with external borders imposes very restrictive constraints on the type of boundary conditions that the fields can satisfy. We analyse the global geometrical and topological properties of the space of all possible boundary conditions for scalar quantum field theories. The variation of the Casimir energy under the change of boundary conditions reveals the existence of singularities generically associated to boundary conditions which either involve topology changes of the underlying physical space or edge states with unbounded below classical energy. The effect can be understood in terms of a new type of Maslov index associated to the non-trivial topology of the space of boundary conditions. We also analyze the global aspects of the renormalization group flow, T-duality and the conformal invariance of the corresponding fixed points.Comment: 11 page

A situational approach to composition

This commentary presents my compositional work of the last two years. It consists of musical pieces that follow a formal approach emphasising static, self-enclosed musical situations. Designed to avoid processual ways of formal organisation, these pieces present collections of rich instrumental textures that do not evolve; they point toward a music of 'being' rather than 'becoming'. Drawing on conceptual traces from discussions of Karlheinz Stockhausen's 'moment form' and Helmut Lachenmann's ideas of 'sound as state'; on musical traces from Morton Feldman and Aldo Clementi, and reflecting on similar approaches by contemporary referents such as Harald Muenz and Bryn Harrison, I seek to contextualise the formal aspects of my own compositional practice comprised in what I call a 'situational' approach. A detailed observation of the musical material and modes of inner organisation used in the construction of these pieces will be necessary in order to reveal the features that give situations their characteristic sense of stasis. I also seek to explore different effective ways of formal organisation based on the co-existence of situations. I do this by means of juxtaposing either single such situations, or several instances of them, reoccurring in different combinations. Both formal approaches seek to emphasise the syntactic independence and lack of relations of consequence between such segments

1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet

We present a detailed NIR/optical/UV study of the transient low mass X-ray binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at determining the nature of its companion star. We obtained three optical spectra at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed optical and NIR photometric observations with both the REM telescope and the New Technology Telescope (NTT) in La Silla. We obtained optical and UV observations from the Swift archive. Finally, we performed optical polarimetry of the source by using the EFOSC2 instrument mounted on the NTT. The optical spectrum of the source is almost featureless since the hydrogen and He I emissions lines, typically observed in LMXBs, are not detected. Similarly, carbon and oxygen lines are neither observed. We marginally detect the He II 4686 AA emission line, suggesting the presence of helium in the accretion disc. No significant optical polarisation level was observed. The lack of hydrogen and He I emission lines in the spectrum implies that the companion is likely not a main sequence star. Driven by the tentative detection of the He II 4686 AA emission line, we suggest that the system could harbour a helium white dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact X-ray binary. By combining an estimate of the mass accretion rate together with evolutionary tracks for a He white dwarf, we obtain a tentative orbital period of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral energy distribution (SED) of the source at two different epochs. One SED was gathered when the source was in the soft X-ray state, and it is consistent with the presence of a single thermal component. The second SED, obtained when the source was in the hard X-ray state, shows a thermal component together with a tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy & Astrophysics (Section 7

Habilidades éticas

Al preguntarnos por la posibilidad de la enseñanza de la ética, se hace necesario contraponer la tradición y la contemporaneidad de la ética, ya que muchas costumbres han transformado la cultura en la cual estamos inmersos. La enseñanza se ha ensanchado o mejor, se ha tecnologizado, mostrando nuevas maneras de ver el mundo. Hasta el momento la enseñanza de la ética se ha inclinado sobre la reflexión basada en contenidos de asuntos morales, pero a partir de ahora, se debe adecuar a las prácticas del diario vivir en la acción misma del hombre. La enseñanza de contenidos en la ética tradicional no lleva más lejos que al manejo de conceptos y contenidos, de quien recibe la instrucción, esto no implica que su mundo fenomenológico se transforme, es decir lo haga práctica. ¿A qué nos lleva esto? Por un lado, no se trata de caer en falsas oposiciones, sino de alcanzar un punto de vista que permita comprender el todo. Comprender el todo es comprender el mundo que se da al sujeto social que se expone como sujeto interactuante, con situaciones propias de su entorno. De esta manera la idea misma de entender el todo se contrapone con la enseñanza de contenidos, ya que los contenidos presentan el problema ético en teoría, y su solución está ya planteada por grandes literatos y en numerosos tomos. De antemano aclararemos que el mundo no se presenta así como lo hacen los libros fruto de las reflexiones de “autoridades literatos

Habilidades éticas

Al preguntarnos por la posibilidad de la enseñanza de la ética, se hace necesario contraponer la tradición y la contemporaneidad de la ética, ya que muchas costumbres han transformado la cultura en la cual estamos inmersos. La enseñanza se ha ensanchado o mejor, se ha tecnologizado, mostrando nuevas maneras de ver el mundo. Hasta el momento la enseñanza de la ética se ha inclinado sobre la reflexión basada en contenidos de asuntos morales, pero a partir de ahora, se debe adecuar a las prácticas del diario vivir en la acción misma del hombre. La enseñanza de contenidos en la ética tradicional no lleva más lejos que al manejo de conceptos y contenidos, de quien recibe la instrucción, esto no implica que su mundo fenomenológico se transforme, es decir lo haga práctica. ¿A qué nos lleva esto? Por un lado, no se trata de caer en falsas oposiciones, sino de alcanzar un punto de vista que permita comprender el todo. Comprender el todo es comprender el mundo que se da al sujeto social que se expone como sujeto interactuante, con situaciones propias de su entorno. De esta manera la idea misma de entender el todo se contrapone con la enseñanza de contenidos, ya que los contenidos presentan el problema ético en teoría, y su solución está ya planteada por grandes literatos y en numerosos tomos. De antemano aclararemos que el mundo no se presenta así como lo hacen los libros fruto de las reflexiones de “autoridades literatos

Augmented Reality Based on SLAM to Assess Spatial Short-Term Memory

Spatial short-term memory is defined as the limited ability of people to retain and remember the location of elements for short periods of time. In this paper, we present the first AR app based on SLAM (Simultaneous Localization and Mapping) to assess spatial short-term memory. A total of 55 participants were involved in a study for remembering the real place where four virtual objects were located in the real environment. The participants were divided into two groups: the ARGroup (the participants learned the location of the virtual objects in the real environment in an adaptation phase using AR) and the NoARGroup (the participants learned the location of the objects by looking at photographs). The results indicated that the performance outcomes in remembering objects and their location for the participants in the ARGroup were statistically significantly greater than those obtained by the participants in the NoARGroup. From this result and our observations, we can conclude that touring the augmented environment helped the participants to better remember the location of virtual objects added to the real scene compared to looking at photographs of the environment. Furthermore, statistically significant differences were not found in relation to gender or age. Finally, our app has several advantages: 1) Our app works in any environment and does not require adding real elements to the environment; 2) the evaluators can select any real environment and place the virtual elements where they want and even change them between sessions; and 3) our app could work similar to the way spatial memory does in everyday life