Thermal conductivity and phonon hydrodynamics in transition metal dichalcogenides from first-principles

We carry out a systematic study of the thermal conductivity of four single-layer transition metal dichalcogenides, MX$_2$ (M = Mo, W; X = S, Se) from first-principles by solving the Boltzmann Transport Equation (BTE). We compare three different theoretical frameworks to solve the BTE beyond the Relaxation Time Approximation (RTA), using the same set of interatomic force constants computed within density functional theory (DFT), finding that the RTA severely underpredicts the thermal conductivity of MS$_2$ materials. Calculations of the different phonon scattering relaxation times of the main collision mechanisms and their corresponding mean free paths (MFP) allow evaluating the expected hydrodynamic behaviour in the heat transport of such monolayers. These calculations indicate that despite of their low thermal conductivity, the present TMDs can exhibit large hydrodynamic effects, being comparable to those of graphene, especially for WSe$_2$ at high temperatures.Comment: 16 pages, 9 figure

La nació i el temple. Patriotisme i Contrareforma a la Catalunya moderna

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El debat de la nació : una nota sobre l'anomenat protonacionalisme

Cap a finals del segle XX la història de les nacions es va començar a escriure -i a concebre- d'una manera radicalment nova. Eric J. Hobsbawm va ser, sens dubte, un dels artífexs d'aquest canvi de paradigma, juntament amb Ernest Gellner, Benedict Anderson i altres autors no pas menys agosarats i iconoclastes. El resultat de tot plegat va ser un trencament amb la historiografia -i la sociologia- clàssica de les nacions; l'esclariment d'algunes controvèrsies antigues; i, finalment, la irrupció d'un cert nombre d'interrogants nous. L'anomenat protonacionalisme -un terme de Hobsbawm mateix- és una d'aquestes qüestions pendents o no del tot solucionades encara. L'autor suggereix que el paradigma modernitzador de la nació guanyaria consistència si hom incorporava l'anàlisi detallada d'algunes trajectòries regionals de l'Europa moderna.Hacia finales del siglo XX la historia de las naciones se empezó a escribir -y a concebir- de una manera radicalmente nueva. Eric J. Hobsbawm fue, sin duda, uno de los artífices de este cambio de paradigma, junto con Ernest Gellner, Benedict Anderson y otros autores no menos osados y iconoclastas. El resultado de todo ello fue una ruptura con la historiografía -y la sociología- clásica de las naciones; el esclarecimiento de algunas controversias antiguas; y, finalmente, la irrupción de un cierto número de interrogantes nuevos. El llamado protonacionalismo -un término de Hobsbawm mismo- es una de estas cuestiones pendientes o no del todo solucionadas todavía. El autor sugiere que el paradigma modernitzador de la nación ganaría consistencia si se incorporaba el análisis detallado de algunas trayectorias regionales de la Europa moderna.At the end of the XX century, a radical new form of writing -and conceiving- the history of nations began. Eric J. Hobsbawm was, without doubt, one the architects of this paradigm shift, as well as Ernest Gellner, Benedict Anderson and others authors who were no less daring and iconoclastic. The result of it all was a breakdown with the classic historiograhy -and sociology- of nations, the clarification of some old controversies and, finally, the breakthrough of a certain number of new questions. The so called protonationalism -a Hobsbawms term- is one of these pending -or not yet full solved- questions. The author suggests that the nation's modernizing paradigm would be more consistent if it incorporated the detailed analysis of some regional paths in the Early Modern Europe

Budget-aware Semi-Supervised Semantic and Instance Segmentation

Methods that move towards less supervised scenarios are key for image segmentation, as dense labels demand significant human intervention. Generally, the annotation burden is mitigated by labeling datasets with weaker forms of supervision, e.g. image-level labels or bounding boxes. Another option are semi-supervised settings, that commonly leverage a few strong annotations and a huge number of unlabeled/weakly-labeled data. In this paper, we revisit semi-supervised segmentation schemes and narrow down significantly the annotation budget (in terms of total labeling time of the training set) compared to previous approaches. With a very simple pipeline, we demonstrate that at low annotation budgets, semi-supervised methods outperform by a wide margin weakly-supervised ones for both semantic and instance segmentation. Our approach also outperforms previous semi-supervised works at a much reduced labeling cost. We present results for the Pascal VOC benchmark and unify weakly and semi-supervised approaches by considering the total annotation budget, thus allowing a fairer comparison between methods.Comment: To appear in CVPR-W 2019 (DeepVision workshop