Activated aging dynamics and negative fluctuation-dissipation ratios

In glassy materials aging proceeds at large times via thermal activation. We show that this can lead to negative dynamical response functions and novel and well-defined violations of the fluctuation-dissipation theorem, in particular, negative fluctuation-dissipation ratios. Our analysis is based on detailed theoretical and numerical results for the activated aging regime of simple kinetically constrained models. The results are relevant to a variety of physical situations such as aging in glass-formers, thermally activated domain growth and granular compaction.Comment: 4 pages, 4 figs; v2 final version (minor modifs) published in Phys. Rev. Let

Properties of short channel ballistic carbon nanotube transistors with ohmic contacts

We present self-consistent, non-equilibrium Green's function calculations of the characteristics of short channel carbon nanotube transistors, focusing on the regime of ballistic transport with ohmic contacts. We first establish that the band lineup at the contacts is renormalized by charge transfer, leading to Schottky contacts for small diameter nanotubes and ohmic contacts for large diameter nanotubes, in agreement with recent experiments. For short channel ohmic contact devices, source-drain tunneling and drain-induced barrier lowering significantly impact the current-voltage characteristics. Furthermore, the ON state conductance shows a temperature dependence, even in the absence of phonon scattering or Schottky barriers. This last result also agrees with recently reported experimental measurements.Comment: Nanotechnology, in pres

Phase ordering and roughening on growing films

We study the interplay between surface roughening and phase separation during the growth of binary films. Already in 1+1 dimension, we find a variety of different scaling behaviors depending on how the two phenomena are coupled. In the most interesting case, related to the advection of a passive scalar in a velocity field, nontrivial scaling exponents are obtained in simulations.Comment: 4 pages latex, 6 figure

Améliorer les apprentissages en sciences en milieu francophone minoritaire : résultats de l’expérimentation d’un modèle pédagogique

Selon les postulats théoriques, les faibles résultats scolaires chez les populations linguistiques minoritaires s’expliqueraient par des facteurs socioculturels et économiques, on recommande donc une pédagogie qui composerait avec ces éléments. Dans le cadre de cette recherche, les auteurs ont créé et expérimenté un modèle pédagogique pour enseigner les sciences en milieu minoritaire tenant compte de ces facteurs. Lors d’une intervention de deux mois, des élèves de cinquième année ont étudié les marais salés à partir de ce modèle pédagogique. L’expression écrite et orale de leurs observations demeurait une priorité. Les résultats ont révélé une attitude positive envers l’approche, un apprentissage scientifique important et une progression lexicale aux niveaux oral et écrit.Socio-cultural and economic factors may in part explain poor academic results for linguistic minorities. In such a case, pedagogical considerations in light of such factors should be put in place. This research created and experimented a pedagogical model for teaching science to minority language students, while considering socio-cultural factors. During a two-month intervention, grade five students studied salt-water marshes in a unit conceived within this model. Oral and written expression of their observations constituted an important part of the experiment. Results indicate a favourable attitude towards the pedagogical approach and progression in science and lexical learning in both written and oral language.Los postulados teóricos indican que los bajos resultados escolares en las poblaciones de lenguas minoritarias se justifican por factores socioculturales y económicos. Por lo tanto, se requiere de una pedagogía que tome en cuenta estos elementos. En el marco de esta investigación, los autores han creado y experimentado un modelo pedagógico para enseñar las ciencias en un ámbito minoritario tomando en cuenta estos factores. En una intervención de una duración de dos meses, alumnos de quinto grado estudiaron las marismas saladas a partir de un modelo pedagógico. Quedó prioritaria la expresión escrita y oral de sus observaciones. Los resultados revelaron una actitud positiva hacia el enfoque, un aprendizaje científico importante así como una progresión lexical a nivel oral y escrito

RLZAP: Relative Lempel-Ziv with Adaptive Pointers

Relative Lempel-Ziv (RLZ) is a popular algorithm for compressing databases of genomes from individuals of the same species when fast random access is desired. With Kuruppu et al.'s (SPIRE 2010) original implementation, a reference genome is selected and then the other genomes are greedily parsed into phrases exactly matching substrings of the reference. Deorowicz and Grabowski (Bioinformatics, 2011) pointed out that letting each phrase end with a mismatch character usually gives better compression because many of the differences between individuals' genomes are single-nucleotide substitutions. Ferrada et al. (SPIRE 2014) then pointed out that also using relative pointers and run-length compressing them usually gives even better compression. In this paper we generalize Ferrada et al.'s idea to handle well also short insertions, deletions and multi-character substitutions. We show experimentally that our generalization achieves better compression than Ferrada et al.'s implementation with comparable random-access times

Rotationally induced Penning ionization of ultracold photoassociated helium dimers

We have studied photoassociation of metastable \tripS helium atoms near the \tripS-\tripP asymptote by both ion detection in a magneto-optical trap and trap-loss measurements in a magnetic trap. A detailed comparison between the results of the two experiments gives insight into the mechanism of the Penning ionization process. We have identified four series of resonances corresponding to vibrational molecular levels belonging to different rotational states in two potentials. The corresponding spin states become quasi-purely quintet at small interatomic distance, and Penning ionization is inhibited by spin conservation rules. Only a weak rotational coupling is responsible for the contamination by singlet spin states leading to a detectable ion signal. However, for one of these series Bose statistics does not enable the rotational coupling and the series detected through trap-loss does not give rise to sufficient ionization for detection.Comment: 7 pages, 4 figures, submitted to EuroPhysics Letter