1,221 research outputs found

    The Perspective Matters! Multisensory Integration in Ego-Centric Reference Frames Determines Full-Body Ownership

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    Recent advances in experimental science have made it possible to investigate the perceptual processes involved in generating a sense of owning an entire body. This is achieved by full-body ownership illusions which make use of specific patterns of visual and somatic stimuli integration. Here we investigate the fundamental question of the reference frames used in the process of attributing an entire body to the self. We quantified the strength of the body-swap illusion in conditions where the participants were observing this artificial body from the perspective of the first or third person. Consistent results from subjective reports and physiological recordings show that the first person visual perspective is critical for the induction of this full-body ownership illusion. This demonstrates that the multisensory integration processes producing the sense of corporeal self operates in an ego-centric reference frame

    Anomalous thickness dependence of the Hall effect in ultrathin Pb layers on Si(111)

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    The magnetoconductive properties of ultrathin Pb films deposited on Si(111) are measured and compared with density-functional electronic band-structure calculations on two-dimensional, free-standing, 1 to 8 monolayers thick Pb(111) slabs. A description with free-standing slabs is possible because it turned out that the Hall coefficient is independent of the substrate and of the crystalline order in the film. We show that the oscillations in sign of the Hall coefficient observed as a function of film thickness can be explained directly from the thickness dependent variations of the electronic bandstructure at the Fermi energy.Comment: 4 pages incl. 3 figures, RevTeX, to appear in Phys. Rev.

    Spectrum of a duality-twisted Ising quantum chain

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    The Ising quantum chain with a peculiar twisted boundary condition is considered. This boundary condition, first introduced in the framework of the spin-1/2 XXZ Heisenberg quantum chain, is related to the duality transformation, which becomes a symmetry of the model at the critical point. Thus, at the critical point, the Ising quantum chain with the duality-twisted boundary is translationally invariant, similar as in the case of the usual periodic or antiperiodic boundary conditions. The complete energy spectrum of the Ising quantum chain is calculated analytically for finite systems, and the conformal properties of the scaling limit are investigated. This provides an explicit example of a conformal twisted boundary condition and a corresponding generalised twisted partition function.Comment: LaTeX, 7 pages, using IOP style

    Particulate matter pollution in African cities

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    Abstract: Rapid urban population growth, air pollution emissions, and changing patterns of disease in African cities may increase the burden of air pollution-related morbidity and mortality in coming decades. Yet, air monitoring is limited across the continent and many countries lack air quality standards. This paper focuses on particulate matter (PM) pollution, one of the most relevant and widely used indicators of urban air quality. We provide an overview of published PM monitoring studies in Africa, outline major themes, point out data gaps, and discuss strategies for addressing particulate air pollution in rapidly growing African cities. Our review reveals that, although few studies have reported annual mean levels of coarse and fine particles, collective evidence from short- and long-term air monitoring studies across urban Africa demonstrates that pollution levels often exceed international guidelines. Furthermore, pollution levels may be rising as a result of increased motor vehicle traffic building on already high background concentrations of PM in many locations due to climatic and geographic conditions. Biomass burning and industrial activities, often located in cities, further exacerbate levels of PM. Despite the health risks this situation presents, air quality programs, particularly in sub-Saharan Africa, have been stalled or discontinued in recent years. Implementation of systematic PM data collection would enable air pollution-related health impact assessments, the development of strategies to reduce the air pollution health burden, and facilitate urban planning and transportation policy as it relates to air quality and health. Keywords Urban air quality, Environmental health, Particulate matter, PM10, PM2.5, Afric

    Owning an overweight or underweight body: distinguishing the physical, experienced and virtual body

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    Our bodies are the most intimately familiar objects we encounter in our perceptual environment. Virtual reality provides a unique method to allow us to experience having a very different body from our own, thereby providing a valuable method to explore the plasticity of body representation. In this paper, we show that women can experience ownership over a whole virtual body that is considerably smaller or larger than their physical body. In order to gain a better understanding of the mechanisms underlying body ownership, we use an embodiment questionnaire, and introduce two new behavioral response measures: an affordance estimation task (indirect measure of body size) and a body size estimation task (direct measure of body size). Interestingly, after viewing the virtual body from first person perspective, both the affordance and the body size estimation tasks indicate a change in the perception of the size of the participant’s experienced body. The change is biased by the size of the virtual body (overweight or underweight). Another novel aspect of our study is that we distinguish between the physical, experienced and virtual bodies, by asking participants to provide affordance and body size estimations for each of the three bodies separately. This methodological point is important for virtual reality experiments investigating body ownership of a virtual body, because it offers a better understanding of which cues (e.g. visual, proprioceptive, memory, or a combination thereof) influence body perception, and whether the impact of these cues can vary between different setups

    From modular invariants to graphs: the modular splitting method

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    We start with a given modular invariant M of a two dimensional su(n)_k conformal field theory (CFT) and present a general method for solving the Ocneanu modular splitting equation and then determine, in a step-by-step explicit construction, 1) the generalized partition functions corresponding to the introduction of boundary conditions and defect lines; 2) the quantum symmetries of the higher ADE graph G associated to the initial modular invariant M. Notice that one does not suppose here that the graph G is already known, since it appears as a by-product of the calculations. We analyze several su(3)_k exceptional cases at levels 5 and 9.Comment: 28 pages, 7 figures. Version 2: updated references. Typos corrected. su(2) example has been removed to shorten the paper. Dual annular matrices for the rejected exceptional su(3) diagram are determine

    Avitaminosis A y trastornos de desarrollo dentoalveolar

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    Several investigations have demonstrated the adverse effects of the hypovitaminosis A in the stomatological field, characterized by ectomesenehyrnal ceIls atrophy and osteoblastic hyperactivity disordered during the phase of the embryonic development; however, the information is limited to the histological manifestations by deficiency in later stages after birth; keeping in mind that we are a country in development with nutritional problems not resolved. The present study was carried out to establish the morphological changes of the dentoalveolar complex present, after birth, for vitamin A deficiency; for which, we used 20 Holstman rats, of 21 days of age, fed with diet of lacking vitamin A, The control group, in addition received weekly one dosis of 100 U.l. of retinol at last to complete the normal dietetic balance. The histological cuts, of rat incisors with avitaminosis A, colored with hematoxilyn and eosin, obtained by conventional methods after the seven and eigth week of experimental phase, Shown in fue odontogenic base acid resistant enamel apposition which goes from 0 to 3 μ of thickness (fig.3), with cylindrical ameloblasts inhibited funcionally and in sorne cases with lost of their plasmatic union complex side conextion. Besides, it shows differentiatinn of bucal adontoblasts with reduced production of dontine matrix and absence of lingual odontoblasts (fig.3), the dental pulp next to the specialized celIs is mesenquimatic and vascularized (Fig.3). The transverse and longitudinal histological cuts of the molars crown with avitaminosis A, shown a pulpodentinary complex with lack of production of predentine, and in some cases almost unexistant. The periodontal complex shown a relative enlargement of the alveolar crest without sign of remodelation (fig.4). The morfological changes of the dentoalveolar complex existent in cases of avitaminosis A, tested with Chi Square al a level of 99% confidence is significant high (see graphics 1-7).Numerosas investigaciones han demostrado los efectos adversos de la hipovitaminosis A en el campo estomatológico, caracterizados por atrofia de las células ectomesenquimales y desordenada hiperactividad osteoblástica durante la fase del desarrollo embrionario; sin embargo, es limitada la información acerca de las manifestaciones histológicas por deficiencia en etapas posteriores al nacimiento; teniendo en cuenta que somos un país en desarrollo con problemas nutricionales no resueltos. El presente estudio se realizó con el objetivo de establecer los cambios morfológicos del complejo dentoalveolar presentes, después del nacimiento, por deficiencia de vitamina A; para lo cual, se empleó 20 ratas Holstman, de 21 días de edad, alimentados con dieta carente de vitamina A. El grupo control en adición recibió semanalmente una dosis de 100 V.L de retinol a fin de completar el balance dietético normal. Los cortes histológicos obtenidos por métodos convencionales, después de 7 y 8 semanas de fase experimental, de incisivos de rata con avitaminosis A, mostraron en la base odontogénica, aposición adamantina ácido resistente, que va de O a 3 M de espesor (Fig.3), con ameloblástos cilindricos funcionalmente inhibidos; en algunos casos, con pérdida de sus conexiones plasmáticas laterales. Además, presenta diferenciación de odontoblastos bucales con reducida producción de matriz dentinaria y ausencia de odontoblastos linguales (Fig.3). La pulpa dentaria adyacente a las células especializadas es mesenquimatosa y vascularizada (Fig.3). Los cortes longitudinales y transversales coronarios de molares de rata con avitaminosis A, muestran un complejo dentinopulpar con escasa producción de predentina, en algunos casos no existe. El complejo periodontal mostró un aparente engrosamiento de la cresta alveolar, sin muestras de remodelación (Fig.4). Los cambios morfológicos del complejo dentoalveolar presente en la avitaminosis A, probado con chi cuadrado a un nivel de confianza del 99%, es altamente significativa (ver gráficos 1-7)

    Evidence on the extent of harms experienced by children as a result of online risks: Implications for policy and research

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    This is an Accepted Manuscript of an article published by Taylor & Francis in Information, Communication and Society on 8/7/2014, available online: http://wwww.tandfonline.com/10.1080/1369118X.2014.934387Intense media and policy focus on issues of online child protection have prompted a resurgence of moral panics about children and adolescents' Internet use, with frequent confounding of different types of risk and harm and little reference to empirical evidence of actual harm. Meanwhile, within the academic literature, the quantity and quality of studies detailing the risks and opportunities of online activity for children and young people has risen substantially in the past 10 years, but this is also largely focused on risk rather than evidence of harm. Whilst this is understandable given the methodological and ethical challenges of studying Internet-related harms to minors, the very concept of risk is dependent on some prior understanding of harm, meaning that without efforts to study what harms are connected with children's online experiences, discussions of risk lack a strong foundation. This article makes a key contribution to the field by reviewing available evidence about the scale and scope of online harms from across a range of disciplines and identifying key obstacles in this research area as well as the major policy implications. The findings are based on a review of 148 empirical studies. Results were found in relation to main types of harms: health-related harms as a result of using pro-eating disorder, self-harm or pro-suicide websites; sex-related harms such as Internet-initiated sexual abuse of minors and cyber-bullying

    Coulomb-gas formulation of SU(2) branes and chiral blocks

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    We construct boundary states in SU(2)kSU(2)_k WZNW models using the bosonized Wakimoto free-field representation and study their properties. We introduce a Fock space representation of Ishibashi states which are coherent states of bosons with zero-mode momenta (boundary Coulomb-gas charges) summed over certain lattices according to Fock space resolution of SU(2)kSU(2)_k. The Virasoro invariance of the coherent states leads to families of boundary states including the B-type D-branes found by Maldacena, Moore and Seiberg, as well as the A-type corresponding to trivial current gluing conditions. We then use the Coulomb-gas technique to compute exact correlation functions of WZNW primary fields on the disk topology with A- and B-type Cardy states on the boundary. We check that the obtained chiral blocks for A-branes are solutions of the Knizhnik-Zamolodchikov equations.Comment: 14 pages, 3 figures, revtex4. Essentially the published versio
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