First-principles quantum transport modeling of thermoelectricity in single-molecule nanojunctions with graphene nanoribbon electrodes

We overview nonequilibrium Green function combined with density functional theory (NEGF-DFT) modeling of independent electron and phonon transport in nanojunctions with applications focused on a new class of thermoelectric devices where a single molecule is attached to two metallic zigzag graphene nanoribbons (ZGNRs) via highly transparent contacts. Such contacts make possible injection of evanescent wavefunctions from ZGNRs, so that their overlap within the molecular region generates a peak in the electronic transmission. Additionally, the spatial symmetry properties of the transverse propagating states in the ZGNR electrodes suppress hole-like contributions to the thermopower. Thus optimized thermopower, together with diminished phonon conductance through a ZGNR/molecule/ZGNR inhomogeneous structure, yields the thermoelectric figure of merit ZT~0.5 at room temperature and 0.5<ZT<2.5 below liquid nitrogen temperature. The reliance on evanescent mode transport and symmetry of propagating states in the electrodes makes the electronic-transport-determined power factor in this class of devices largely insensitive to the type of sufficiently short conjugated organic molecule, which we demonstrate by showing that both 18-annulene and C10 molecule sandwiched by the two ZGNR electrodes yield similar thermopower. Thus, one can search for molecules that will further reduce the phonon thermal conductance (in the denominator of ZT) while keeping the electronic power factor (in the nominator of ZT) optimized. We also show how often employed Brenner empirical interatomic potential for hydrocarbon systems fails to describe phonon transport in our single-molecule nanojunctions when contrasted with first-principles results obtained via NEGF-DFT methodology.Comment: 20 pages, 6 figures; mini-review article prepared for the special issue of the Journal of Computational Electronics on "Simulation of Thermal, Thermoelectric, and Electrothermal Phenomena in Nanostructures", edited by I. Knezevic and Z. Aksamij

Diabetes Mellitus: fatores de risco em uma instituição de ensino na área da saúde Los factores de riesgo para los Diabetes Mellitus tipo 2 de institución de enseñanza Type-2 Diabetes Mellitus: risk factors in a school in the health field

O objetivo deste estudo é identificar os fatores de risco para o diabetes mellitus tipo 2. Os resultados indicam a necessidade de programa educativo junto às instituições, visando despertar nos sujeitos a busca de estilos de vida saudáveis a fim de prevenir os fatores de risco para o diabetes tipo 2.<br>El objetivo del estudio es identificar los factores de riesgo para la diabetes mellitus de tipo 2. Los resultados muestran la necesidad de un programa educativo junto con las instituciones, buscando despertar en los sujetos la necesidad de buscar un estilo de vida saludable con el fin de prevenir los factores de riesgo para la diabetes tipo 2.<br>This work aims at identifying the risks factors of type-2 diabetes mellitus. The results show the need of an education program in institutions aiming at making the subjects aware of the necessity to look for healthy life styles in order to prevent the risks factors of type-2 diabetes