Zero-point length, extra-dimensions and string T-duality

In this paper, we are going to put in a single consistent framework apparently unrelated pieces of information, i.e. zero-point length, extra-dimensions, string T-duality. More in details we are going to introduce a modified Kaluza-Klein theory interpolating between (high-energy) string theory and (low-energy) quantum field theory. In our model zero-point length is a four dimensional ``virtual memory'' of compact extra-dimensions length scale. Such a scale turns out to be determined by T-duality inherited from the underlying fundamental string theory. From a low energy perspective short distance infinities are cut off by a minimal length which is proportional to the square root of the string slope, i.e. \sqrt{\alpha^\prime}. Thus, we provide a ``bridge'' between the ultra-relativistic string domain and the low energy arena of point-particle quantum field theory.Comment: 28 pages, Latex, no figures; two references adde

Tackling Higher Derivative Ghosts with the Euclidean Path Integral

An alternative to the effective field theory approach to treat ghosts in higher derivative theories is to attempt to integrate them out via the Euclidean path integral formalism. It has been suggested that this method could provide a consistent framework within which we might tolerate the ghost degrees of freedom that plague, among other theories, the higher derivative gravity models that have been proposed to explain cosmic acceleration. We consider the extension of this idea to treating a class of terms with order six derivatives, and find that for a general term the Euclidean path integral approach works in the most trivial background, Minkowski. Moreover we see that even in de Sitter background, despite some difficulties, it is possible to define a probability distribution for tensorial perturbations of the metric.Comment: 21 page

La formation des enseignantes et des enseignants à l’égalité des chances filles-garçons : une utopie ?

En France, la Convention interministérielle du 25 février 2000 pour la promotion de l’égalité des chances entre les filles et les garçons de même qu’entre les femmes et les hommes dans le système éducatif préconise la tenue de séances d’information destinés aux différentes catégories de personnel de l’ensemble de la communauté éducative et le recours à des modules de formation pour le personnel enseignant. À partir de son expérience de formation des enseignantes et des enseignants à l’égalité des chances dans le système éducatif, l’auteure met en évidence et analyse leurs résistances, que ce soit en formation initiale ou continue.The inter-ministerial Convention of 25/02/00 for the promotion of equal opportunity for girls and boys, women and men in the education system recommends information sessions for staff in the entire education community and training modules for teachers.From our experience in teacher training in equal opportunity for girls and boys, women and men in the education system, we shall highlight and analyse teacher resistance in initial and continuing training

Efficient Nearest Neighbors Search for Large-Scale Landmark Recognition

The problem of landmark recognition has achieved excellent results in small-scale datasets. When dealing with large-scale retrieval, issues that were irrelevant with small amount of data, quickly become fundamental for an efficient retrieval phase. In particular, computational time needs to be kept as low as possible, whilst the retrieval accuracy has to be preserved as much as possible. In this paper we propose a novel multi-index hashing method called Bag of Indexes (BoI) for Approximate Nearest Neighbors (ANN) search. It allows to drastically reduce the query time and outperforms the accuracy results compared to the state-of-the-art methods for large-scale landmark recognition. It has been demonstrated that this family of algorithms can be applied on different embedding techniques like VLAD and R-MAC obtaining excellent results in very short times on different public datasets: Holidays+Flickr1M, Oxford105k and Paris106k

Weak intrinsic charge transfer complexes: A new route for developing wide spectrum organic photovoltaic cells

Solar emission extends in the near IR and one of the main issues in designing organic solar cells resides in extending the response into the near IR. Here we show that this may be achieved by making intimate interpenetrated networks of C60 and Zn-phthalocyanine (Zn-Pc) in the solid. Various spectroscopic investigations of co-sublimated thin films of C60 and Zn-phthalocyanine give indeed ample evidence of the existence of a weak charge transfer (CT) state at 1.4 eV, which quenches the photoluminescence of both molecules. The films produced by co-sublimation undergo to a spinodal decomposition producing domains prevalently constituted by Zn-Pc in contact with domain prevalently of C60. The domains size depends on the deposition conditions (rate, stoichiometry, and substrate temperature) forming a percolating 3D network. The separation in different domains is confirmed by the observation of two overlapping peaks, in the resonant Raman spectrum, that correspond to the Ag(2) pinch mode (C=C double bond stretching) for pristine C60 and for a partially (~0.25e) doped one. This indicates that only those donor molecules at the grain boundary, which are in contact with C60, give rise to a renormalized new CT ground state. Photocurrent measurements of interpenetrated networks of C60 and Zn-Pc show a linear dependence with respect to the incident light as a consequence of direct absorption within the CT state. The CT state favors the charge separation between the two components, when it is inserted as interface in the organic photovoltaic p - n junction thus increasing the efficiency of the device