Conductivity of Coulomb interacting massless Dirac particles in graphene: Regularization-dependent parameters and symmetry constraints

We compute the Coulomb correction $\mathcal{C}$ to the a. c. conductivity of interacting massless Dirac particles in graphene in the collisionless limit using the polarization tensor approach in a regularization independent framework. Arbitrary parameters stemming from differences between logarithmically divergent integrals are fixed on physical grounds exploiting only spatial $O(2)$ rotational invariance of the model which amounts to transversality of the polarization tensor. Consequently $\mathcal{C}$ is unequivocally determined to be $(19- 6\pi)/12$ within this effective model. We compare our result with explicit regularizations and discuss the origin of others results for $\mathcal{C}$ found in the literature

Ultraviolet and Infrared Divergences in Implicit Regularization: a Consistent Approach

Implicit Regularization is a 4-dimensional regularization initially conceived to treat ultraviolet divergences. It has been successfully tested in several instances in the literature, more specifically in those where Dimensional Regularization does not apply. In the present contribution we extend the method to handle infrared divergences as well. We show that the essential steps which rendered Implicit Regularization adequate in the case of ultraviolet divergences have their counterpart for infrared ones. Moreover we show that a new scale appears, typically an infrared scale which is completely independent of the ultraviolet one. Examples are given.Comment: 9 pages, version to appear in Mod. Phys. Lett.

Ecosocioeconomics applied to urban freight by bicycle and motorcycle in the city of Curitiba, Brazil

The aim of this work is to compare the logistics of urban light weight delivery by motorcycle and bicycle. To this purpose, a case study in the city of Curitiba, Brazil, was chosen. City planning demands alternative solutions to everyday problems, among which use of urban space and mobility are relevant due to fast and rather chaotic growing. Urban mobility −a complex network comprising a variety of actors and areas; has social, economic and environmental impacts that might be underestimated in planning and implementation of actions. So far, and for the case studied here, urban planning for light weight delivery has not included externalities, but rather focused on technical issues on logistics and urban traffic. For instance, the rates of dead and disability from accidents on this mobility are currently very high. In the present research, two light weight deliveries actually used in Curitiba were compared: motorbikes and bicycles. The analysis is based on the methodology of the eco-socio-economy of organizations. This approach considers the complexity of subsystems linked, and the effectiveness beyond the organization but on the social demands in the urban territory. The use of bicycles was studied using data from EcoBike, analyzed here and compared to the generic case of deliveries by motorbikes. Indicators for accidents (with and without death), fossil energy used, CO2 emissions, and operative costs were obtained and compared. The indicators assessed favour the use of bicycles over motorbikes.Fil: García, M.. Pontifícia Universidade Católica do Paraná; BrasilFil: Sampaio, C. A. C.. Pontifícia Universidade Católica do Paraná; BrasilFil: Gonzalez, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Patagonia Norte. Instituto de Investigación en Biodiversidad y Medioambiente; Argentina. Universidad Nacional del Comahue; Argentin

Composite materials with MWCNT processed by Selective Laser Sintering for electrostatic discharge applications

Selective Laser Sintering (SLS) is an additive manufacturing technology that enables the production of polymeric parts for end-use applications. Despite the great potential of conventional materials, carbon-based reinforcements have been widely considered to contradict the electrically insulating nature of polymers, allowing the applicability of SLS in novel applications within electronics industry. However, the laser-sintering processing of such materials still encompasses a number of limitations including agglomeration problems, weak interparticle adhesion, low parts resolution, high processing time and costs. Therefore, this research reports the development of functional composite materials for SLS capable of being considered for the production of components that are in direct contact with electrostatic discharge (ESD) sensitive devices. To do so, composite materials of Polyamide 12 incorporating 0.50 wt%, 1.75 wt% and 3.00 wt% of Multi-Walled Carbon Nanotubes were developed aiming to achieve values of surface resistance between 104 - 109 Ω, according to the delivery instructions of Bosch Car Multimedia S.A. Test specimens produced by SLS were dimensionally, mechanically, electrically, thermally and morphologically characterized. Comparing to the neat matrix, the composite materials revealed narrower SLS processing window, reduced mechanical strength, surface resistance in the ESD range and electrical conductivity until 10−6 S/cm. Fundamentals on the sintering process of these functional materials are also provided.This work was co-funded by the European Regional Development Fund through the Operational Competitiveness and Internationalization Programme (COMPETE 2020) [Project No. 47108, “SIFA”; Funding Reference: POCI-01-0247-FEDER-047108] and by the Foundation for Science and Technology (FCT) through the PhD scholarship 2020.04520.BD