Exponential decay of spin-spin correlation between distant defect states produced by contour hydrogenation of polycyclic aromatic hydrocarbon molecules

The first few low-lying spin states of alternant polycyclic aromatic hydrocarbon (PAH) molecules of several shapes showing defect states induced by contour hydrogenation have been studied both by ab initio methods and by a precise numerical solution of Pariser-Parr-Pople (PPP) interacting model. In accordance with Lieb's theorem, the ground state shows a spin multiplicity equal to one for balanced molecules, and it gets larger values for imbalanced molecules (that is, when the number of π electrons on both subsets is not equal). Furthermore, we find a systematic decrease of the singlet-triplet splitting as a function of the distance between defects, regardless of whether the ground state is singlet or triplet. For example, a splitting smaller than 0.001 eV is obtained for a medium size C46H28 PAH molecule (di-hydrogenated [11]phenacene) showing a singlet ground state. We conclude that π electrons unbound by lattice defects tend to remain localized and unpaired even when long-range Coulomb interaction is taken into account. Therefore they show a biradical character (polyradical character for more than two defects) and should be studied as two or more local doublets. The implications for electron transport are potentially important since these unpaired electrons can trap traveling electrons or simply flip their spin at a very small energy cost.

3D teaching: the ideal complement for professionals in design and construction

Today, the requirement of professional skills to university students is constantly increasing in our society. In our opinion, the content offered in official degrees need to be nourished with different variables, enriching their global professional knowledge in a parallel way; that is why, in recent years, there is a great multiplicity of complementary courses at university. One of the most socially demanded technical requirements within the architectural, design or engineering field is the management of 3D drawing software, becoming an indispensable reality in these sectors. Thus, this specific training becomes essential over two-dimension traditional design, because the inclusion of great possibilities of spatial development that go beyond conventional orthographic projections (plans, sections or elevations), allowing modelling and rotation of the selected items from multiple angles and perspectives. Therefore, this paper analyzes the teaching methodology of a complementary course for those technicians in the construction industry interested in computer-aided design, using modelling (SketchupMake) and rendering programs (Kerkythea). The course is developed from the technician point of view, by learning computer management and its application to professional development from a more general to a more specific view through practical examples. The proposed methodology is based on the development of real examples in different professional environments such as rehabilitation, new constructions, opening projects or architectural design. This multidisciplinary contribution improves criticism of students in different areas, encouraging new learning strategies and the independent development of three-dimensional solutions. Thus, the practical implementation of new situations, even suggested by the students themselves, ensures active participation, saving time during the design process and the increase of effectiveness when generating elements which may be represented, moved or virtually tested. In conclusion, this teaching-learning methodology improves the skills and competencies of students to face the growing professional demands of society. After finishing the course, technicians not only improved their expertise in the field of drawing but they also enhanced their capacity for spatial vision; both essential qualities in these sectors that can be applied to their professional development with great success.

Technologies for Seduction: The “Espacio Doméstico” VideoArt Center in Blanca [EDOM]

Sustainability, understood in its beginnings as a common horizon for multiple practices and fields of study, has gradually given way to the development of increasingly sophisticated tools, with distinct dominant meanings established for each discipline. Within the field of material technologies for architectural production, sustainability seems to have found its most fertile ground in topics such as recycling, the use of "bio" materials, or energetic efficiency. However, to improve the understanding of the impact of technology on our ways of living, it appears increasingly necessary to move from the deterministic logic of sustainability into the relational domain of ecology, where the use and deployment of technologies can be observed through the multiplicity of its effects and the diversity of actors involved. In this paper we will address the case of the rehabilitation of several traditional houses located in the Murcian town of Blanca to host the “Espacio Doméstico” VideoArt Center (EDOM). In this action the selection and implementation of technologies have been aimed at impacting on diverse aspects including local communities, digital manufacturing, recycling, and policies regarding the rehabilitation of heritage buildings. While the initial approach was to address housing recovery as a heterogeneous accumulation of stories, technologies or material deployments of the domestic, our intervention strategies ascribed to the different technologies the role of mediating with existing elements through the incorporation of the very different visions of sustainability. Thus, we displayed artifacts produced by digitally manufactured methacrylate assembled on IKEA structures, fluorescent power lines supported by insulators on the wall, fluorescent tattoos on walls and ceilings that guide and extend the configuration of existing flooring, esparto furniture and fabrics produced by the esparto women workers’ and village women’s associations, re-appropriations of old furniture through the implementation of new media technologies, etc. If we can see seduction as the process of converting affinities and disagreements into affirmative communication, then the EDOM proposal can be seen as an active seduction process between technologies and users who approach this kind of cultural artifacts. Through these permanently active processes, art technologies will refer the viewer to complex sensory experiences, where a combination of parody, memory and sound pushes the user to the limit of mere comprehension of works of art. This more relational approach to the issue of heritage rehabilitation, technology or art institutions is offered as an area of controversy and debate on the scope of political ecology and its potential impact on the architect’s professional practice.