Non-conventional graphene superlattices as electron band-pass filters

Electron transmission through different non-conventional (non-uniform barrier height) gated and gapped graphene superlattices (GSLs) is studied. Linear, Gaussian, Lorentzian and Pöschl-Teller superlattice potential profiles have been assessed. A relativistic description of electrons in graphene as well as the transfer matrix method have been used to obtain the transmission properties. We find that it is not possible to have perfect or nearly perfect pass bands in gated GSLs. Regardless of the potential profile and the number of barriers there are remanent oscillations in the transmission bands. On the contrary, nearly perfect pass bands are obtained for gapped GSLs. The Gaussian profile is the best option when the number of barriers is reduced, and there is practically no difference among the profiles for large number of barriers. We also find that both gated and gapped GSLs can work as omnidirectional band-pass filters. In the case of gated Gaussian GSLs the omnidirectional range goes from −50° to 50° with an energy bandwidth of 55 meV, while for gapped Gaussian GSLs the range goes from −80° to 80° with a bandwidth of 40 meV. Here, it is important that the energy range does not include remanent oscillations. On the light of these results, the hole states inside the barriers of gated GSLs are not beneficial for band-pass filtering. So, the flatness of the pass bands is determined by the superlattice potential profile and the chiral nature of the charge carriers in graphene. Moreover, the width and the number of electron pass bands can be modulated through the superlattice structural parameters. We consider that our findings can be useful to design electron filters based on non-conventional GSLs

Propiedades de transmisión de electrones de Dirac a través de superredes Cantor en grafeno

En este trabajo usamos el método de la matriz de transferencia para estudiar el tunelamiento de los electrones de Dirac a través de superredes aperiodicas en grafeno. Consideramos una hoja de grafeno depositada encima de bloques de sustratos de Óxido de Silicio (SiO2) y Carburo de Silicio (SiC), en los cuales aplicamos la serie de Cantor. Calculamos la transmitancia para diferentes parámetros fundamentales tales como: ancho de partida, energía de incidencia, ángulo de incidencia y número de generación de la serie de Cantor. En este caso, la transmitancia como función de la energía presenta rasgos autosimilares al variar el número de generación. También computamos la distribución angular de la transmitancia para energías fijas econtrando un patrón autosimilar entre generaciones. Por último, calculamos los factores de escala para algunos espectros de la transmitancia, los cuales efectivamente muestran escalabilidad.In this work we use the transfer matrix method to study the tunneling of Dirac electrons through aperiodic monolayer graphene superlattices. We consider a graphene sheet deposited on top of slabs of Silicon-Oxide (SiO2) and Silicon-Carbide (SiC) substrates, in which we applied the Cantor's series. We calculate the transmittance for different fundamental parameters such as: starting width, incident energy, incident angle and generation number of the Cantor's series. In this case, the transmittance as function of energy presents self-similar features as a function of the generation number. We also compute the angular distribution of the transmittance for fixed energies finding a self-similar patterns between generations. Finally, we calculate the scaling factor for some transmittance spectra, which effectively show scalability

Transmittance and Absorption Properties of Graphene Multilayer Quasi-periodic Structure: Period-Doubling case

Graphene is a two dimensional material of special interest due to its unusual electronic, mechanical, chemical, optical among other properties, which suggest a wide range of applications in optoelectronics, computer, ecology, etc. The study of the optical properties of graphene is important due to its potential applications such as ultrafast photonics, optical filters, composite materials, photovoltaics and energy storage device. In this work we study the transmission and absorption properties of a quasi-regular multilayer dielectric-graphene- dielectric system. The multilayer structure is built on the quasi-regular Period-Doubling (PD) sequence. The optical response of graphene takes into account intra-band and inter-band transitions. We use the transfer-matrix method to calculate the transmission and absorption spectra. It is obtained a strong dependence on the number of layers in the system, the width of dielectric media and the optical contrast. Furthermore, we calculate the spectra for both transverse magnetic (TM) and transverse electric (TE) polarization in the infrared region.En este trabajo nosotros estudiamos las propiedades de transmisión y Absorción de un sistema multicapa cuasiregular dieléctrico-grafeno-dieléctrico. La estructura multicapa está construida en base a una secuencia cuasi-regular Period-Doubling (PD). La respuesta óptica de el grafeno toma en cuenta las transiciones intra-banda e inter-banda. Nosotros usamos el método de matriz de transferencia para calcular los espectros de transmisión y absorción. Esto mostró una fuerte dependencia con el número de capas de sistema, el espesor de los medios dieléctricos y el contraste óptico. Además nosotros calculamos los espectros para la polarización transversal Magnética (TM) y transversal eléctrica (TE) en la región de frecuencia del infrarojo

Study of the optical properties of dielectric-graphene-dielectric multilayer quasi-periodic structures: Thue-Morse case

Potential applications in optoelectronics had generated a great interest on the study of graphene optical properties. Along with this, graphene has exceptional properties such as high mobility and optical transparency, flexibility, mechanical robustness, etc. Due to these properties, graphene could be used in different devices such as transparent conductors, organic light-emitting diodes, photodetectors, touch screens, saturable absorbers and ultrafast lasers. A transfer-matrix method is used in order to calculate graphene optical properties, such as transmission, and absorption in the infrared region. The quasi-periodic structure consists in intercalated graphene sheets between two consecutives dielectrics. The dielectric materials follow the Thue-Morse sequence (ThMo). The graphene sheets are described by the optical conductivity considering interband and intraband transitions. The structure of the spectra depends strongly on the number of sequence generation, width of the different dielectrics and dielectric permittivity. In our case, the infrared region corresponds to a chemical potential greater than kT. In the calculated spectra, the geometrical properties of the Thue-Morse sequence can be observed. We obtain absorption bands well defined.En este estudio se usó el método de Matriz de Transferencia para calcular las propiedades ópticas de Transformación y Absorción en la región infrarroja. La estructura estudiada consiste en un arreglo cuasi-periódico intercalando láminas de grafeno entre dos dieléctricos consecutivos. Los materiales dieléctricos siguen una secuencia Thue-Morse (ThMo). Las láminas de grafeno son descritas por medio de su conductividad óptica considerando las transiciones interbanda e intrabanda. La estructura de los espectros depende fuertemente del número de generación, espesor de los diferentes dieléctricos y de la permitividad de los dieléctricos. En nuestro caso, en la región infrarroja corresponde a una región donde el potencial químico del grafeno es mucho mayor que kT. En los espectros obtenidos, las propiedades geométricas de la secuencia Thue-Morse puede ser observada. Nosotros obtenemos bandas de absorción bien definidas

TM plasmonic modes in a multilayer graphene-dielectric structure

Optical and electronic properties of multilayer systems have been extensively studied in the last years due to its potential applications in high-performance optoelectronic and photonic devices. In particular, the role of plasmonic modes is critical in such systems leading to improvements in solar cells efficiency, detection of biosensors, Raman signal enhancement, among others. In this work, we study the plasmonic modes in a multilayer system composed of graphene layers embedded within dielectric materials. The dispersion relation of plasmonic modes is obtained by calculating the poles of reflectivity using the transfer matrix method. We show the attenuated total reflection spectra for a multilayer graphene-dielectric structure, and determine the optimum distance between the prism and the multilayer system for detecting graphene plasmons in the Otto configuration. Additional to the well-known plasmonics bands, when we consider the interband and intraband contribution of graphene's conductivity, and large wavevectors parallel to graphene's plane, all plasmonic bands have an asymptotic behavior. Besides, an upper mode emerges. Finally, it is important to highlight that the number of branches in the plasmonic relation dispersion depend on the number of graphene sheets

Digital light processing-3D printing of thermoset materials with high biodegradability from amino acid-derived acrylamide monomers

Six acrylamide resins, derived from l-phenylalanine and l-leucine, are designed for application in digital light processing (DLP) printers to obtain biodegradable thermoset polymers. The acrylamide copolymers are prepared under light irradiation at 405 nm and thermal post-curing processes. Low molecular weight poly(ethylene glycol)diacrylate (PEGDA) and N,N-dimethylacrylamide (DMAM), both liquid resins, are used as co-monomers and diluents for the amino acid-derived acrylamide solubilization. The presence of two phenylalanine units and two ester groups in the acrylamide monomer accuses a fast degradation rate in hydrolytic medium in 90 days. The residual products leached in the aqueous media prove to be non-cytotoxic, when 3D-printed samples are cultured with osteoblast cells (MG63), which represents an advantage for the safe disposal of printer waste materials. The scaled-up pieces derived from l-phenylalanine and diethylene glycol, as amino acid-derived acrylamide (named compound C), PEGDA and DMAM, present high dimensional stability after DLP printing of complex structures used as testing samples. Layers of 50 µm of thickness are well cohesive having isotropic behavior, as demonstrated with tensile-strain measurements performed in X–Y–Z (plane) directions. The compound C, which contains phenylalanine amino acid, reveals a promising potential to replace non-biodegradable acrylate polymers used in prototyping systems.Postprint (author's final draft

Efectividad de las Promociones por medio de Facebook en los consumidores jóvenes con edades entre los 18 a 35 años, en el primer semestre del año 2010

Proyecto de graduación (Licenciatura en Administración de Empresas. Enfasis de Mercadeo) Instituto Tecnológico de Costa Rica, 2010Esta investigación se desarrolla con la finalidad de entender cuál es el nivel de efectividad de las promociones en un tema tan amplio como lo es Facebook en Costa Rica. Esta red social ha adquirido gran relevancia y popularidad entre los usuarios e importancia para otros medios de comunicación, para organizaciones, para grupos políticos y sociales. Estudios recientes nacionales e internacionales muestran que conforme transcurre el tiempo las personas pasan mayor cantidad de tiempo conectadas a internet y se dedican menos a ver televisión o a leer una revista. Esto significa que Internet y las redes sociales se han convertido en un medio de comunicación muy importante donde las personas no solo se informan, sino que también comparten su forma de pensar en temas de actualidad. Internet es un espacio que permite a las personas socializar, reconectarse con viejos amigos, hacer nuevos amigos, en general interactuar. Este cambio de cultura tiene un impacto fuerte en el mercadeo, ya que internet, se ha convertido en el medio con más presencia en las generaciones jóvenes, es el único o al menos el principal canal por el que le pueden llegar a muchas personas, aprovechando que muchas de las características de los usuarios y futuros clientes se encuentran disponibles en sus perfiles de Facebook. Es así como muchas empresas costarricenses han incorporado a Facebook en su estrategia de mercadeo, ya que éste permite a las empresas interactuar con sus clientes actuales y potenciales, además sumarlo como parte de la estrategia de mercadeo les genera menor costo que otros medios.Instituto Tecnológico de Costa Rica. Escuela Administración de Empresas

Antigenotoxic Effect of Chamomilla recutita (L.) Rauschert Essential Oil in Mouse Spermatogonial Cells, and Determination of Its Antioxidant Capacity in Vitro

Chamomilla recutita (L.) Rauschert (Asteraceae), popularly known as chamomile, is a plant used in traditional medicine for various therapeutic purposes. Chamomile essential oil (CEO) is particularly known to inhibit the genotoxic damage produced by mutagens in mice somatic cells. The aim of this research was to determine the inhibitory potential of CEO on the genotoxic damage produced by daunorubicin (DAU) in mice germ cells. We evaluated the effect of 5, 50, and 500 mg/kg of essential oil on the rate of sister chromatid exchange (SCE) induced in spermatogonia by 10 mg/kg of the mutagen. We found no genotoxicity of CEO, but detected an inhibition of SCE after the damage induced by DAU; from the lowest to the highest dose of CEO we found an inhibition of 47.5%, 61.9%, and 93.5%, respectively. As a possible mechanism of action, the antioxidant capacity of CEO was determined using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging method and ferric thiocyanate assays. In the first test we observed a moderate scavenging potential of the oil; nevertheless, the second assay showed an antioxidant capacity similar to that observed with vitamin E. In conclusion, we found that CEO is an efficient chemoprotective agent against the damage induced by DAU in the precursor cells of the germinal line of mice, and that its antioxidant capacity may induce this effect

The Effects of Low Volume Versus High Volume Sled-Push Training on Muscular Adaptation

Abstracts PURPOSE This study aimed to compare the effects of low-volume and high-volume sled-push resistance training on muscle strength, power, and body composition. METHODS Twenty-four college students were recruited and matched based on baseline one-repetition maximum (1-RM) into one of the three groups: 1) low volume (LV) resistance training, 2) high volume (HV) resistance training, or 3) control (CON) (n=8 per group). The LV training consisted of five single repetitions of pushing a weighted sled for 9.1 m. The HV training consisted of three sets of five repetitions of pushing a weighted sled for 9.1 m. Training consisted of three weekly workouts performed on nonconsecutive days for 6 weeks. This study utilized a pre-test and post-test design consisting of 1-RM, Wingate power test, standing long jump, vertical jump, and body composition. RESULTS After 6 weeks of training, there was a similar but significant increase in 1-RM in both training groups (pre-test: LV=226.8±14.8 kg vs. HV=217.7±19.5 kg; post-test: LV=298.5±15 kg vs. HV=286.9±16 kg, p.05). CONCLUSIONS The results suggested that low-volume resistance training was as effective as a high-volume protocol for improving muscle strength. However, the present study was unable to determine the effects on muscle power and body composition

TRY plant trait database - enhanced coverage and open access

Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives