Landau level transitions indoped graphene in a time dependent magnetic field

The aim of this work is to describe the Landau levels transitions of Bloch electrons in doped graphene with an arbitrary time dependent magnetic field in the long wavelength approximation. In particular, transitions from the m Landau level to the m + 1 and m + 2 Landau levels are studied using time-dependent perturbation theory. Time intervals are computed in which transition probabilities tend to zero at low order in the coupling constant. In particular, Landau level transitions are studied in the case of Bloch electrons travelling in the direction of the applied magnetic force and the results are compared with classical and revival periods of electrical current in graphene. Finally, current probabilities are computed for the n = 0 and n = 1 Landau levels showing expected oscillating behavior with modified cyclotron frequency.Comment: 18 pages, 7 figure

Ideal isotropic auxetic networks from random networks

Auxetic materials are characterized by a negative Poisson's ratio, $\mathrm{\nu}$. As the Poisson's ratio becomes negative and approaches the lower isotropic mechanical limit of $\mathrm{\nu = -1}$, materials show enhanced resistance to impact and shear, making them suitable for applications ranging from robotics to impact mitigation. Past experimental efforts aimed at reaching the $\mathrm{\nu = -1}$ limit have resulted in highly anisotropic materials, which show a negative Poisson's ratio only when subjected to deformations along specific directions. Isotropic designs have only attained moderately auxetic behavior, or have led to structures that cannot be manufactured in 3D. Here, we present a design strategy to create isotropic structures from disordered networks that leads to Poisson's ratios as low as $\mathrm{\nu = -0.98}$. The materials conceived through this approach are successfully fabricated in the laboratory and behave as predicted. The Poisson's ratio $\mathrm{\nu}$ is found to depend on network structure and bond strengths; this sheds light on the structural motifs that lead to auxetic behavior. The ideas introduced here can be generalized to 3D, a wide range of materials, and a spectrum of length scales, thereby providing a general platform that could impact technology.Comment: 16 pages, 6 figure

Olfactory function in focal epilepsies: Understanding mesial temporal lobe epilepsy beyond the hippocampus

Several lines of research have linked olfactory regions with the pathophysiology of focal epilepsies. Among those regions, the piriform cortex represents the major part of the primary olfactory cortex. According to these data, we raised the hypothesis that in patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis exists an interictal dysfunction of olfactory processing that could be more significant compared to patients with extra‐hippocampal focal epilepsy and healthy controls. This could be the consequence of a dysfunctional epileptogenic network that extends beyond the hippocampus and affects other structures, including the piriform cortex. To test this hypothesis, we evaluated the olfactory function with the Sniffin' Sticks test in 32 patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis, 30 patients with extra‐hippocampal focal epilepsy, and 22 healthy controls. Compared to the other study groups, patients with temporal lobe epilepsy due to hippocampal sclerosis showed a basal olfactory dysfunction characterized by an impairment in odor discrimination and odor identification. We also found that high seizure frequency had a strong correlation with the evaluated olfactory tasks. Our results are consistent with neuroimaging and neuropathological data that establish a link between olfactory regions and the pathophysiology of temporal lobe epileps

Effect of Sn content on Pt/ CNT electrocatalysts for direct ethanol fuel cell application

Several bimetallic PtSn catalysts supported on multiwalled carbon nanotubes for ethanol electro-oxidation were prepared by conventional impregnation-reduction method. The Pt loading was kept at 20 wt.% and Pt:Sn atomic ratios of 5:1, 3:1, and 1:1 were selected. The catalysts were structurally characterized by temperature programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, H2 chemisorption, cyclohexane dehydrogenation reaction, and transmission electron microscopy. The electrochemical characterization of the electrocatalytic materials was carried out in acid medium by cyclic voltammetry, linear sweep voltammetry, chronoamperometry, and CO stripping techniques. Among the different stoichiometries tested, the Pt(20)Sn(12.17)/CNT catalyst exhibited the highest electrocatalytic activity for ethanol oxidation reaction, with mass current density of 189.5 mA mgPt−1 at 796 mV (vs. Ag/AgCl).Fil: Azcoaga Chort, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Nagel, Pablo A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Veizaga, Natalia Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Rodriguez, Virginia Ines. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: de Miguel, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; Argentin

Anterobasal temporal lobe lesions alter recurrent functional connectivity within the ventral pathway during naming

An increasing amount of evidence supports a crucial role for the anterior temporal lobe (ATL) in semantic processing. Critically, a selective disruption of the functional connectivity between left and right ATLs in patients with chronic aphasic stroke has been illustrated. The aim of the current study was to evaluate the consequences that lesions on the ATL have on the neurocognitive network supporting semantic cognition. Unlike previous work, in this magnetoencephalography study we selected a group of patients with small lesions centered on the left anteroventral temporal lobe before surgery. We then used an effective connectivity method (i.e., dynamic causal modeling) to investigate the consequences that these lesions have on the functional interactions within the network. This approach allowed us to evaluate the directionality of the causal interactions among brain regions and their associated connectivity strengths. Behaviorally, we found that semantic processing was altered when patients were compared with a strictly matched group of controls. Dynamic causal modeling for event related responses revealed that picture naming was associated with a bilateral frontotemporal network, encompassing feedforward and feedback connections. Comparison of specific network parameters between groups revealed that patients displayed selective network adjustments. Specifically, backward connectivity from anterior to posterior temporal lobe was decreased in the ipsilesional hemisphere, whereas it was enhanced in the contralesional hemisphere. These results reinforce the relevance of ATL in semantic memory, as well as its amodal organization, and highlight the role of feedback connections in enabling the integration of the semantic information.This work was supported by a research grant from the Spanish Ministry of Science and Innovation (Grant SAF2011-27920) to I.G.-M. P.C. was supported by a Ramo´n y Cajal Fellowship from the Spanish Ministry of Science and Innovation (RYC-2010-05748). C.P. was supported by Spanish Ministry of Science and Education (AP2009-4131)

Reconstructing Paleoflood Occurrence and Magnitude from Lake Sediments

Lake sediments are a valuable archive to document past flood occurrence and magnitude, and their evolution over centuries to millennia. This information has the potential to greatly improve current flood design and risk assessment approaches, which are hampered by the shortness and scarcity of gauge records. For this reason, paleoflood hydrology from lake sediments received fast-growing attention over the last decade. This allowed an extensive development of experience and methodologies and, thereby, the reconstruction of paleoflood series with increasingly higher accuracy. In this review, we provide up-to-date knowledge on flood sedimentary processes and systems, as well as on state-of-the-art methods for reconstructing and interpreting paleoflood records. We also discuss possible perspectives in the field of paleoflood hydrology from lake sediments by highlighting the remaining challenges. This review intends to guide the research interest in documenting past floods from lake sediments. In particular, we offer here guidance supported by the literature in how: to choose the most appropriate lake in a given region, to find the best suited sedimentary environments to take the cores, to identify flood deposits in the sedimentary sequence, to distinguish them from other instantaneous deposits, and finally, to rigorously interpret the flood chronicle thus produced.publishedVersio

Arquitectura distribuida para un sistema soporte de decisiones globales

En este trabajo presentamos el diseño de una arquitectura distribuida para un Sistema Soporte de Decisiones global prototipo en desarrollo en el GIDSATD (Grupo de Investigación y desarrollo de Sistemas de Ayuda a la Toma de Decisiones). El prototipo del SSD consta de doce módulos diseñados para operar en forma “autónoma”. En este trabajo presentamos la arquitectura distribuida propuesta para el SSD, describiendo la partición del sistema, los requerimientos de cada módulo y un esquema de interacción. El modelo propuesto para la distribución del SSD global prototipo se ha basado en un mecanismo de comportamiento orientado a eventos, el cual ha permitido lograr una arquitectura en la que cada módulo se mantiene relativamente autónomo cooperando entre sí a través de un esquema de interacción que establece un bajo nivel de acoplamiento. De esta manera, logramos reflejar la forma natural de trabajo del sistema. Para esto, el diseño de la arquitectura de distribución del SSD no se ajustó a las características de un estilo arquitectónico definido, sino que se buscó el modelo más apropiado para el SSD. Por esta razón dicho modelo no satisface todas las características de un estilo. Además, el diseño se ha realizado de modo independiente de la tecnología de comunicación utilizada para implementarlo. Finalmente, para implementar la arquitectura distribuida propuesta para el SSD prototipo, se decidió utilizar la tecnología de Computación de Objetos Distribuidos, seleccionando al standard CORBA del OMG. Este tipo de middleware provee herramientas de alto nivel de abstracción para: Especificar interfaces orientadas a objetos que permiten definir los “contratos” entre los módulos del SSD y encapsularlos. Permite también establecer un esquema de comunicación asincrónico y desacoplado entre objetos de distintos módulos mediante un mecanismo denominado publicar/suscribir. De este modo, encontramos en esta tecnología el soporte a las características requeridas por el diseño propuesto.Sistemas Distribuidos - Redes Concurrencia - Sesión de póstersRed de Universidades con Carreras en Informática (RedUNCI

Arquitectura distribuida para un sistema soporte de decisiones globales

En este trabajo presentamos el diseño de una arquitectura distribuida para un Sistema Soporte de Decisiones global prototipo en desarrollo en el GIDSATD (Grupo de Investigación y desarrollo de Sistemas de Ayuda a la Toma de Decisiones). El prototipo del SSD consta de doce módulos diseñados para operar en forma “autónoma”. En este trabajo presentamos la arquitectura distribuida propuesta para el SSD, describiendo la partición del sistema, los requerimientos de cada módulo y un esquema de interacción. El modelo propuesto para la distribución del SSD global prototipo se ha basado en un mecanismo de comportamiento orientado a eventos, el cual ha permitido lograr una arquitectura en la que cada módulo se mantiene relativamente autónomo cooperando entre sí a través de un esquema de interacción que establece un bajo nivel de acoplamiento. De esta manera, logramos reflejar la forma natural de trabajo del sistema. Para esto, el diseño de la arquitectura de distribución del SSD no se ajustó a las características de un estilo arquitectónico definido, sino que se buscó el modelo más apropiado para el SSD. Por esta razón dicho modelo no satisface todas las características de un estilo. Además, el diseño se ha realizado de modo independiente de la tecnología de comunicación utilizada para implementarlo. Finalmente, para implementar la arquitectura distribuida propuesta para el SSD prototipo, se decidió utilizar la tecnología de Computación de Objetos Distribuidos, seleccionando al standard CORBA del OMG. Este tipo de middleware provee herramientas de alto nivel de abstracción para: Especificar interfaces orientadas a objetos que permiten definir los “contratos” entre los módulos del SSD y encapsularlos. Permite también establecer un esquema de comunicación asincrónico y desacoplado entre objetos de distintos módulos mediante un mecanismo denominado publicar/suscribir. De este modo, encontramos en esta tecnología el soporte a las características requeridas por el diseño propuesto.Sistemas Distribuidos - Redes Concurrencia - Sesión de póstersRed de Universidades con Carreras en Informática (RedUNCI

Long-range effects in granular avalanching

We introduce a model for granular flow in a one-dimensional rice pile that incorporates rolling effects through a long-range rolling probability for the individual rice grains proportional to $r^{-\rho}$, $r$ being the distance traveled by a grain in a single topling event. The exponent $\rho$ controls the average rolling distance. We have shown that the crossover from power law to stretched exponential behaviors observed experimentally in the granular dynamics of rice piles can be well described as a long-range effect resulting from a change in the transport properties of individual grains. We showed that stretched exponential avalanche distributions can be associated with a long-range regime for $1<\rho<2$ where the average rolling distance grows as a power law with the system size, while power law distributions are associated with a short range regime for $\rho>2$, where the average rolling distance is independent of the system size.Comment: 5 pages, 3 figure