The symplectic origin of conformal and Minkowski superspaces

Supermanifolds provide a very natural ground to understand and handle supersymmetry from a geometric point of view; supersymmetry in $d=3,4,6$ and $10$ dimensions is also deeply related to the normed division algebras. In this paper we want to show the link between the conformal group and certain types of symplectic transformations over division algebras. Inspired by this observation we then propose a new\,realization of the real form of the 4 dimensional conformal and Minkowski superspaces we obtain, respectively, as a Lagrangian supermanifold over the twistor superspace $\mathbb{C}^{4|1}$ and a big cell inside it. The beauty of this approach is that it naturally generalizes to the 6 dimensional case (and possibly also to the 10 dimensional one) thus providing an elegant and uniform characterization of the conformal superspaces.Comment: 15 pages, references added, minor change

Reply Comment: Comparison of Approaches to Classical Signature Change

We contrast the two approaches to ``classical" signature change used by Hayward with the one used by us (Hellaby and Dray). There is (as yet) no rigorous derivation of appropriate distributional field equations. Hayward's distributional approach is based on a postulated modified form of the field equations. We make an alternative postulate. We point out an important difference between two possible philosophies of signature change --- ours is strictly classical, while Hayward's Lagrangian approach adopts what amounts to an imaginary proper ``time" on one side of the signature change, as is explicitly done in quantum cosmology. We also explain why we chose to use the Darmois-Israel type junction conditions, rather than the Lichnerowicz type junction conditions favoured by Hayward. We show that the difference in results is entirely explained by the difference in philosophy (imaginary versus real Euclidean ``time"), and not by the difference in approach to junction conditions (Lichnerowicz with specific coordinates versus Darmois with general coordinates).Comment: 10 pages, latex, no figures. Replying to - "Comment on `Failure of Standard Conservation Laws at a Classical Change of Signature'", S.A. Hayward, Phys. Rev. D52, 7331-7332 (1995) (gr-qc/9606045

La revue scientifique : un élément d’analyse des sciences humaines et sociales

L’article se propose d’aborder la question de la structuration du champ des sciences humaines et sociales, en prenant pour “entrée” les revues scientifiques de ces disciplines, en particulier dans le cas de la production scientifique marocaine. Il s’agit, à travers l’analyse de la structure et du fonctionnement d’un ensemble de revues de sciences humaines et sociales, de montrer que cette production constitue un indice de la structuration de ce champ scientifique. L’article montre notamment qu’à une focalisation disciplinaire correspond un certain recentrage des revues sur elles-mêmes — donc un certain regroupement des chercheurs autour d’objets scientifiques, de normes de publication, ou encore de modèles de traitement de ces objets. Par ailleurs, des supports de publication comme les revues se resserrent autour de certains objets scientifiques, et doivent probablement l’importance croissante de leur noyau de contributeurs à cette spécialisation et à la visibilité peu à peu acquise par la revue ; en somme, à un certain monopole de la production scientifique.Mots clefs: Maroc – Sciences humaines et sociales – Revues scientifiques – Champ – Structur

Using Ground Transportation for Aviation System Disruption Alleviation

An investigation was made into whether passenger delays and airline costs due to disruptive events affecting European airports could be reduced by a coordinated strategy of using alternative flights and ground transportation to help stranded passengers reach their final destination using airport collaborative decision-making concepts. Optimizing for airline cost for hypothetical disruptive events suggests that, for airport closures of up to 10 h, airlines could benefit from up to a 20% reduction in passenger delay-related costs. The mean passenger delay could be reduced by up to 70%, mainly via a reduction in very long delays

Stochastic Tachyon Fluctuations, Marginal Deformations and Shock Waves in String Theory

Starting with exact solutions to string theory on curved spacetimes we obtain deformations that represent gravitational shock waves. These may exist in the presence or absence of sources. Sources are effectively induced by a tachyon field that randomly fluctuates around a zero condensate value. It is shown that at the level of the underlying conformal field theory (CFT) these deformations are marginal and moreover all \a'-corrections are taken into account. Explicit results are given when the original undeformed 4-dimensional backgrounds correspond to tensor products of combinations of 2-dimensional CFT's, for instance SL(2,R)/R \times SU(2)/U(1).Comment: 26 pages, harvmac, no figures. Very minor modifications, and in addition conditions (B.3) and (B.4) were also obtained using beta-function equations. Version to appear in Phys. Rev.

The exclusion of indigenous traditional knowledge in the higher education : the case of traditional medicine and the Mexican medical education

This paper analyzes the level of inclusion of indigenous traditional knowledge about traditional medicine in Mexican medical training, showing an angle of the place that maintains cultural diversity in higher education nationally. Using a quantitative, cross-sectional, exploratory and descriptive design, instruments were applied to survey the 85 institutions registered with the Mexican Association of Colleges and Schools of Medicine (known by its Spanish acronym AMFEM); the data were analyzed quantitatively and qualitatively. Of these institutions, only 27.05% include teaching about traditional medicine in 36 subjects related to the topic, 50% of which is optional, 41.66% of short duration, 52.62% with few credit hours and, in some cases, with a pejorative orientation. It is noted that the area of the Mexican medical education reflects a broader political problem of asymmetry and inequality between stakeholders and their knowledge, so that the rejection of indigenous traditional knowledge in the Mexican medical education is only a reflection of the many other places where these groups, and their knowledge, have been excluded before

Methods of pattern classification for the design of a NIRS-based brain computer interface.

Brain-Computer Interface (BCI) is a communication system that offers the possibility to act upon the surrounding environment without using our nervous systems efferent pathways. One of the most important parts of a BCI is the pattern classification system which allows to translate mental activities into commands for an external device. This work aims at providing new pattern classification methods for the development of a Brain Computer Interface based on Near Infrared Spectroscopy. To do so, a thorough study of machine learning techniques used for developing BCIs has been conducted

Dynamical Determination of the Metric Signature in Spacetime of Nontrivial Topology

The formalism of Greensite for treating the spacetime signature as a dynamical degree of freedom induced by quantum fields is considered for spacetimes with nontrivial topology of the kind ${\bf R}^{D-1} \times {\bf T}^1$, for varying $D$. It is shown that a dynamical origin for the Lorentzian signature is possible in the five-dimensional space ${\bf R}^4 \times {\bf T}^1$ with small torus radius (periodic boundary conditions), as well as in four-dimensional space with trivial topology. Hence, the possibility exists that the early universe might have been of the Kaluza-Klein type, \ie multidimensional and of Lorentzian signature.Comment: 10 pages, LaTeX file, 4 figure

Methods of pattern classification for the design of a NIRS-based brain computer interface.

Brain-Computer Interface (BCI) is a communication system that offers the possibility to act upon the surrounding environment without using our nervous systems efferent pathways. One of the most important parts of a BCI is the pattern classification system which allows to translate mental activities into commands for an external device. This work aims at providing new pattern classification methods for the development of a Brain Computer Interface based on Near Infrared Spectroscopy. To do so, a thorough study of machine learning techniques used for developing BCIs has been conducted

<i>atonal-</i> and <i>achaete-scute</i>-related genes in the annelid <i>Platynereis dumerilii</i>: insights into the evolution of neural basic-Helix-Loop-Helix genes

Background: Functional studies in model organisms, such as vertebrates and Drosophila, have shown that basic Helix-loop-Helix ( bHLH) proteins have important roles in different steps of neurogenesis, from the acquisition of neural fate to the differentiation into specific neural cell types. However, these studies highlighted many differences in the expression and function of orthologous bHLH proteins during neural development between vertebrates and Drosophila. To understand how the functions of neural bHLH genes have evolved among bilaterians, we have performed a detailed study of bHLH genes during nervous system development in the polychaete annelid, Platynereis dumerilii, an organism which is evolutionary distant from both Drosophila and vertebrates. Results: We have studied Platynereis orthologs of the most important vertebrate neural bHLH genes, i.e. achaete-scute, neurogenin, atonal, olig, and NeuroD genes, the latter two being genes absent of the Drosophila genome. We observed that all these genes have specific expression patterns during nervous system formation in Platynereis. Our data suggest that in Platynereis, like in vertebrates but unlike Drosophila, ( i) neurogenin is the main proneural gene for the formation of the trunk central nervous system, (ii) achaetescute and olig genes are involved in neural subtype specification in the central nervous system, in particular in the specification of the serotonergic phenotype. In addition, we found that the Platynereis NeuroD gene has a broad and early neuroectodermal expression, which is completely different from the neuronal expression of vertebrate NeuroD genes. Conclusion: Our analysis suggests that the Platynereis bHLH genes have both proneural and neuronal specification functions, in a way more akin to the vertebrate situation than to that of Drosophila. We conclude that these features are ancestral to bilaterians and have been conserved in the vertebrates and annelids lineages, but have diverged in the evolutionary lineage leading to Drosophila