1,877 research outputs found
On the Influence of Spatial Dispersion on the Performance of Graphene-Based Plasmonic Devices
We investigate the effect of spatial dispersion phenomenon on the performance
of graphene-based plasmonic devices at THz. For this purpose, two different
components, namely a phase shifter and a low-pass filter, are taken from the
literature, implemented in different graphene-based host waveguides, and
analyzed as a function of the surrounding media. In the analysis, graphene
conductivity is modeled first using the Kubo formalism and then employing a
full- model which accurately takes into account spatial dispersion. Our
study demonstrates that spatial dispersion up-shifts the frequency response of
the devices, limits their maximum tunable range, and degrades their frequency
response. Importantly, the influence of this phenomenon significantly increases
with higher permittivity values of the surrounding media, which is related to
the large impact of spatial dispersion in very slow waves. These results
confirm the necessity of accurately assessing non-local effects in the
development of practical plasmonic THz devices.Comment: 5 pages, 18 figures, 2 table
Sinusoidally-Modulated Graphene Leaky-Wave Antenna for Electronic Beamscanning at THz
This paper proposes the concept, analysis and design of a
sinusoidally-modulated graphene leaky-wave antenna with beam scanning
capabilities at a fixed frequency. The antenna operates at terahertz
frequencies and is composed of a graphene sheet transferred onto a
back-metallized substrate and a set of polysilicon DC gating pads located
beneath it. In order to create a leaky-mode, the graphene surface reactance is
sinusoidally-modulated via graphene's field effect by applying adequate DC bias
voltages to the different gating pads. The pointing angle and leakage rate can
be dynamically controlled by adjusting the applied voltages, providing
versatile beamscanning capabilities. The proposed concept and achieved
performance, computed using realistic material parameters, are extremely
promising for beamscanning at THz frequencies, and could pave the way to
graphene-based reconfigurable transceivers and sensors.Comment: 7 pages; 10 figure
Diversidad y endemismos de reptiles en la Puna del NOA
La conservación de la biodiversidad es uno de los grandes objetivos y desafíos de los biólogos contemporáneos. Los principales problemas que enfrentan quienes deben cumplir este objetivo es que los recursos y la capacidad de conservar son limitados y por ello se deben aplicar criterios que permitan elegir áreas que maximicen el esfuerzo de protección. La identificación de áreas de endemismo es uno de ellos.Fil: Diaz Gomez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina; Argentina. Universidad Nacional de Salta; ArgentinaFil: Quinteros, Andres Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Salta. Instituto de Bio y Geociencias del Noroeste Argentino; Argentina; Argentina. Universidad Nacional de Salta; Argentin
Integral Equation Analysis of Plane Wave Scattering by Coplanar Graphene-Strip Gratings in the THz Range
The plane wave scattering and absorption by finite and infinite gratings of
free-space standing infinitely long graphene strips are studied in the THz
range. A novel numerical approach, based on graphene surface impedance,
hyper-singular integral equations, and the Nystrom method, is proposed. This
technique guarantees fast convergence and controlled accuracy of computations.
Reflectance, transmittance, and absorbance are carefully studied as a function
of graphene and grating parameters, revealing the presence of surface plasmon
resonances. Specifically, larger graphene relaxation times increases the number
of resonances in the THz range, leading to higher wave transmittance due to the
reduced losses; on the other hand an increase of graphene chemical potential
up-shifts the frequency of plasmon resonances. It is also shown that a
relatively low number of graphene strips (>10) are able to reproduce Rayleigh
anomalies. These features make graphene strips good candidates for many
applications, including tunable absorbers and frequency selective surfaces.Comment: 11 pages, 26 figure
Analyzing hippocampal synaptic damage and glial response in a mouse model of tauopathy
Tau pathology is highly related to synaptic and neuronal loss, leading to cognitive decline and dementia in Alzheimer’s disease (AD) and other tauopathies. Tau transgenic mice are widely used to investigate the specific contribution of this protein to AD since they reproduce the synaptic and cognitive dysfunction in parallel to an age-dependent accumulation of hyperphosphorylated forms of tau (phospho-tau). The aim of this study was to investigate the progression of tau aggregation and analyze its relationship with microglial activation and synaptic damage within the hippocampus of a transgenic tau model. 2, 6, 9, 12 and 18 month-old THY-Tau22 transgenic and WT mice were analyzed. Tau pathology was assessed by western blotting and immunohistochemistry (AT8, AT100). Confocal microscopy was used to study microglial/phospho-tau relationship, and Thioflavin-S staining to evidence fibrillar aggregates. Levels of general (Synaptophysin) and subtype-specific (ChAT, VGAT, VGLUT-1) synaptic proteins were determined by WB and immunohistochemistry. Inflammatory markers were assessed by quantitative PCR (CD45, CD68, TREM2), immunohistochemistry (Iba-1) and image analysis. Tau pathology was detectable in the hippocampus from 2 months of age and increased progressively during aging. Presynaptic protein levels were significantly decreased from 9-12 months compared to age-matched WT mice. Even though some inflammatory markers were slightly increased in the hippocampus, microglial reactivity was found to be generally attenuated and some cells even exhibited reduction in their prolongations and a clear degenerative phenotype at advanced ages similar to that seen in the hippocampus of AD patients. Finally, this model could be a relevant tool to further understand the specific role of tau in both microglial response and synaptic pathology in AD.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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