Composition-induced structural transitions in mixed rare-gas clusters

The low-energy structures of mixed Ar--Xe and Kr--Xe Lennard-Jones clusters are investigated using a newly developed parallel Monte Carlo minimization algorithm with specific exchange moves between particles or trajectories. Tests on the 13- and 19- atom clusters show a significant improvement over the conventional basin-hopping method, the average search length being reduced by more than one order of magnitude. The method is applied to the more difficult case of the 38-atom cluster, for which the homogeneous clusters have a truncated octahedral shape. It is found that alloys of dissimilar elements (Ar--Xe) favor polytetrahedral geometries over octahedra due to the reduced strain penalty. Conversely, octahedra are even more stable in Kr--Xe alloys than in Kr_38 or Xe_38, and they show a core-surface phase separation behavior. These trends are indeed also observed and further analysed on the 55-atom cluster. Finally, we correlate the relative stability of cubic structures in these clusters to the glassforming character of the bulk mixtures.Comment: 14 pages, 8 figures, 5 tables PRB vol 70, in pres

Enhancing single-parameter quantum charge pumping in carbon-based devices

We present a theoretical study of quantum charge pumping with a single ac gate applied to graphene nanoribbons and carbon nanotubes operating with low resistance contacts. By combining Floquet theory with Green's function formalism, we show that the pumped current can be tuned and enhanced by up to two orders of magnitude by an appropriate choice of device length, gate voltage intensity and driving frequency and amplitude. These results offer a promising alternative for enhancing the pumped currents in these carbon-based devices.Comment: 3.5 pages, 2 figure

Fractional generalization of Fick's law: a microscopic approach

In the study of transport in inhomogeneous systems it is common to construct transport equations invoking the inhomogeneous Fick law. The validity of this approach requires that at least two ingredients be present in the system. First, finite characteristic length and time scales associated to the dominant transport process must exist. Secondly, the transport mechanism must satisfy a microscopic symmetry: global reversibility. Global reversibility is often satisfied in nature. However, many complex systems exhibit a lack of finite characteristic scales. In this Letter we show how to construct a generalization of the inhomogeneous Fick law that does not require the existence of characteristic scales while still satisfying global reversibility.Comment: 4 pages. Published versio

Uniform non-stoichiometric titanium nitride thin films for improved kinetic inductance detector array

We describe the fabrication of homogeneous sub-stoichiometric titanium nitride films for microwave kinetic inductance detector (mKID) arrays. Using a 6 inch sputtering target and a homogeneous nitrogen inlet, the variation of the critical temperature over a 2 inch wafer was reduced to <25 %. Measurements of a 132-pixel mKID array from these films reveal a sensitivity of 16 kHz/pW in the 100 GHz band, comparable to the best aluminium mKIDs. We measured a noise equivalent power of NEP = 3.6e-15 W/Hz^(1/2). Finally, we describe possible routes to further improve the performance of these TiN mKID arrays.Comment: 7 pages, 4 figures, submitted to Journal of low temperature physics, Proceedings of LTD-1

A Train-on-Target Strategy for Multilingual Spoken Language Understanding

[EN] There are two main strategies to adapt a Spoken Language Understanding system to deal with languages different from the original (source) language: test-on-source and train-on-target. In the train-ontarget approach, a new understanding model is trained in the target language, which is the language in which the test utterances are pronounced. To do this, a segmented and semantically labeled training set for each new language is needed. In this work, we use several general-purpose translators to obtain the translation of the training set and we apply an alignment process to automatically segment the training sentences. We have applied this train-on-target approach to estimate the understanding module of a Spoken Dialog System for the DIHANA task, which consists of an information system about train timetables and fares in Spanish. We present an evaluation of our train-on-target multilingual approach for two target languages, French and EnglishThis work has been partially funded by the project ASLP-MULAN: Audio, Speech and Language Processing for Multimedia Analytics (MEC TIN2014-54288-C4-3-R).García-Granada, F.; Segarra Soriano, E.; Millán, C.; Sanchís Arnal, E.; Hurtado Oliver, LF. (2016). A Train-on-Target Strategy for Multilingual Spoken Language Understanding. Lecture Notes in Computer Science. 10077:224-233. https://doi.org/10.1007/978-3-319-49169-1_22S22423310077Benedí, J.M., Lleida, E., Varona, A., Castro, M.J., Galiano, I., Justo, R., López de Letona, I., Miguel, A.: Design and acquisition of a telephone spontaneous speech dialogue corpus in Spanish: DIHANA. In: LREC 2006, pp. 1636–1639 (2006)Calvo, M., Hurtado, L.-F., García, F., Sanchís, E.: A Multilingual SLU system based on semantic decoding of graphs of words. In: Torre Toledano, D., Ortega Giménez, A., Teixeira, A., González Rodríguez, J., Hernández Gómez, L., San Segundo Hernández, R., Ramos Castro, D. (eds.) IberSPEECH 2012. CCIS, vol. 328, pp. 158–167. Springer, Heidelberg (2012). doi: 10.1007/978-3-642-35292-8_17Calvo, M., Hurtado, L.F., Garca, F., Sanchis, E., Segarra, E.: Multilingual spoken language understanding using graphs and multiple translations. Comput. Speech Lang. 38, 86–103 (2016)Dinarelli, M., Moschitti, A., Riccardi, G.: Concept segmentation and labeling for conversational speech. In: Interspeech, Brighton, UK (2009)Esteve, Y., Raymond, C., Bechet, F., Mori, R.D.: Conceptual decoding for spoken dialog systems. In: Proceedings of EuroSpeech 2003, pp. 617–620 (2003)García, F., Hurtado, L., Segarra, E., Sanchis, E., Riccardi, G.: Combining multiple translation systems for spoken language understanding portability. In: Proceedings of IEEE Workshop on Spoken Language Technology (SLT), pp. 282–289 (2012)Hahn, S., Dinarelli, M., Raymond, C., Lefèvre, F., Lehnen, P., De Mori, R., Moschitti, A., Ney, H., Riccardi, G.: Comparing stochastic approaches to spoken language understanding in multiple languages. IEEE Trans. Audio Speech Lang. Process. 6(99), 1569–1583 (2010)He, Y., Young, S.: A data-driven spoken language understanding system. In: Proceedings of ASRU 2003, pp. 583–588 (2003)Hurtado, L., Segarra, E., García, F., Sanchis, E.: Language understanding using n-multigram models. In: Vicedo, J.L., Martínez-Barco, P., Muńoz, R., Saiz Noeda, M. (eds.) EsTAL 2004. LNCS (LNAI), vol. 3230, pp. 207–219. Springer, Heidelberg (2004). doi: 10.1007/978-3-540-30228-5_19Jabaian, B., Besacier, L., Lefèvre, F.: Comparison and combination of lightly supervised approaches for language portability of a spoken language understanding system. IEEE Trans. Audio Speech Lang. Process. 21(3), 636–648 (2013)Koehn, P., et al.: Moses: open source toolkit for statistical machine translation. In: Proceedings of ACL Demonstration Session, pp. 177–180 (2007)Lafferty, J., McCallum, A., Pereira, F.: Conditional random fields: probabilistic models for segmenting and labeling sequence data. In: International Conference on Machine Learning, pp. 282–289. Citeseer (2001)Lefèvre, F.: Dynamic Bayesian networks and discriminative classifiers for multi-stage semantic interpretation. In: IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP 2007, vol. 4, pp. 13–16. IEEE (2007)Ortega, L., Galiano, I., Hurtado, L.F., Sanchis, E., Segarra, E.: A statistical segment-based approach for spoken language understanding. In: Proceedings of InterSpeech 2010, Makuhari, Chiba, Japan, pp. 1836–1839 (2010)Segarra, E., Sanchis, E., Galiano, M., García, F., Hurtado, L.: Extracting semantic information through automatic learning techniques. IJPRAI 16(3), 301–307 (2002)Servan, C., Camelin, N., Raymond, C., Bchet, F., Mori, R.D.: On the use of machine translation for spoken language understanding portability. In: Proceedings of ICASSP 2010, pp. 5330–5333 (2010)Tür, G., Mori, R.D.: Spoken Language Understanding: Systems for Extracting Semantic Information from Speech, 1st edn. Wiley, Hoboken (2011

Geometric magic numbers of sodium clusters: Interpretation of the melting behaviour

Putative global minima of sodium clusters with up to 380 atoms have been located for two model interatomic potentials. Structures based upon the Mackay icosahedra predominate for both potentials, and the magic numbers for the Murrell-Mottram model show excellent agreement with the sizes at which maxima in the latent heat and entropy change at melting have been found in experiment.Comment: 4 pages, 2 figure

Melting of aluminium clusters

The melting of Al clusters in the size range 49 <= N <= 62 has been studied using two model interatomic potentials. The results for the two models are significantly different. The glue potential exhibits a smooth relatively featureless heat capacity curve for all sizes except for N = 54 and N = 55, sizes at which icosahedral structures are favoured over the polytetrahedral. Gupta heat capacity curves, instead, show a well-defined peak that is indicative of a first-order-like transition. The differences between the two models reflect the different ground-state structures, and neither potential is able to reproduce or explain the size dependence of the melting transition recently observed in experiments