A L\'evy flight for electrons in graphene: superdiffusive-to-diffusive transport transition

In this work we propose an electronic L\'evy flight device, analogous to a recent optical realization. To that end, we investigate the transmission of electrons in graphene nanoribbons in the presence of circular electrostatic clusters, whose diameter follow a power-law distribution. We analyze the effect of the electrostatic clusters on the electronic transport regime of the nanoribbons, in terms of its diffusion behavior. Our numerical calculations show that the presence of circular electrostatic clusters induces a transition from L\'evy (superdiffusive) to diffusive transport as the energy increases. Furthermore, we argue that in our electronic L\'evy flight device, superdiffusive transport is an exclusive feature of the low-energy quantum regime, while diffusive transport is a feature of the semiclassical regime. Therefore, we attribute the observed transition to the chiral symmetry breaking, once the energy moves away from the Dirac point of graphene.Comment: Accepted for publication as a Regular Article in Physical Review

Cannabinoid CB1 receptor antagonism markedly increases dopamine receptor-mediated stereotypies

The contribution of the endocannabinoid system to dopamine-mediated disorganized behavior in schizophrenia is discussed. We used a model of concurrent stimulation of dopamine D1 and D2 receptors to evaluate the role of this system in dopamine-mediated stereotypies measured in a hole-board test. Pretreatment with the cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A; 1 mg/kg) potentiated stereotyped behavior induced by coadministration of the dopamine D1 receptor agonist SKF 38393 (0.05, 0.1 and 1 mg/kg) and the dopamine D2 receptor agonist quinpirole (0.25 mg/kg). Thus, the endocannabinoid system acts as a brake for abnormal behavior associated with dopaminergic overactivation. © 2007 Elsevier B.V. All rights reserved.Peer Reviewe

Analysis of the putative role of CR1 in Alzheimer’s disease: Genetic association, expression and function

Chronic activation of the complement system and induced inflammation are associated with neuropathology in Alzheimer's disease (AD). Recent large genome wide association studies (GWAS) have identified single nucleotide polymorphisms (SNPs) in the C3b/C4b receptor (CR1 or CD35) that are associated with late onset AD. Here, anti-CR1 antibodies (Abs) directed against different epitopes of the receptor, were used to localize CR1 in brain, and relative binding affinities of the CR1 ligands, C1q and C3b, were assessed by ELISA. Most Abs tested stained red blood cells in blood vessels but showed no staining in brain parenchyma. However, two monoclonal anti-CR1 Abs labeled astrocytes in all of the cases tested, and this reactivity was preabsorbed by purified recombinant human CR1. Human brain-derived astrocyte cultures were also reactive with both mAbs. The amount of astrocyte staining varied among the samples, but no consistent difference was conferred by diagnosis or the GWAS-identified SNPs rs4844609 or rs6656401. Plasma levels of soluble CR1 did not correlate with diagnosis but a slight increase was observed with rs4844609 and rs6656401 SNP. There was also a modest but statistically significant increase in relative binding activity of C1q to CR1 with the rs4844609 SNP compared to CR1 without the SNP, and of C3b to CR1 in the CR1 genotypes containing the rs6656401 SNP (also associated with the larger isoform of CR1) regardless of clinical diagnosis. These results suggest that it is unlikely that astrocyte CR1 expression levels or C1q or C3b binding activity are the cause of the GWAS identified association of CR1 variants with AD. Further careful functional studies are needed to determine if the variant-dictated number of CR1 expressed on red blood cells contributes to the role of this receptor in the progression of AD, or if another mechanism is involved

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

The status of the world's land and marine mammals: diversity, threat, and knowledge

Knowledge of mammalian diversity is still surprisingly disparate, both regionally and taxonomically. Here, we present a comprehensive assessment of the conservation status and distribution of the world's mammals. Data, compiled by 1700+ experts, cover all 5487 species, including marine mammals. Global macroecological patterns are very different for land and marine species but suggest common mechanisms driving diversity and endemism across systems. Compared with land species, threat levels are higher among marine mammals, driven by different processes (accidental mortality and pollution, rather than habitat loss), and are spatially distinct (peaking in northern oceans, rather than in Southeast Asia). Marine mammals are also disproportionately poorly known. These data are made freely available to support further scientific developments and conservation action

Paradoxos da “identidade nacional” nos discursos arquitetônicos de Lucio Costa e Sylvio de Vasconcellos

n the debate about the period and the architectural style that represented the national identity in the historiography of Brazilian architecture, in the first decades of the twentieth century, different agents took place in the consolidation of the architectural heritage idea. Important characters in cultural preservation policies, such as Rodrigo Melo Franco de Andrade and Mário de Andrade, integrated the public space emphasizing their positions of organic intellectuals in cultural policies. Given this fact, this article focuses on the consolidation in the social imaginary of eighteenth-century architecture as an effective representation of national architecture, consolidating itself as a style/period with the largest number of buildings listed until 1970. Understanding the different subjects involved in this process, this article focuses on the effective political action of Lucio Costa and Sylvio Vasconcellos on the defense of colonial heritage, based on texts and interventions in the overturned cities throughout Brazil, shaping and consolidating their strategies around an ideology of heritage and nation. In addition, we seek to understand the direct relationship established by both agents between the “elected” national heritage architecture and the precepts of the new architectural practice linked to the Modern Movement, to which they were adherents. Justifying the new from the primitive, in a perfect relationship where everything can be explained and fitted, the eclectic architecture was treated as a copy of styles, exacerbation of ornaments and link to foreignism, in opposition at the claimed nation project. We should always review concepts and guidelines, dealing more truthfully and fairly with our eclectic heritage, and consequently with our architectural historiography.No debate em torno do período e do estilo arquitetônico que representassem a identidade nacional na historiografia da arquitetura brasileira, nas primeiras décadas do século XX, diferentes agentes tomaram lugar na consolidação do ideário patrimonial arquitetônico. Figuras marcantes às políticas de preservação cultural, tais como Rodrigo Melo Franco de Andrade e Mário de Andrade, integraram o espaço público ressaltando suas posições de intelectuais inerentes às políticas culturais. Tendo em vista tal fato, este artigo se debruça sobre a consolidação no imaginário social da arquitetura setecentista enquanto efetiva representação da arquitetura nacional, concretizando-se enquanto estilo/período com o maior número de edificações tombadas até 1970. Compreendendo os diferentes sujeitos envolvidos nesse processo, centra-se, assim, na efetiva ação política de Lucio Costa e Sylvio Vasconcellos na defesa em torno do patrimônio colonial, a partir de textos e intervenções nas cidades tombadas Brasil afora, conformandoe consolidando suas estratégias em torno de um ideário de patrimônio e nação. Além disso, busca-se compreender a relação direta estabelecida por ambos os agentes entre a arquitetura “eleita” patrimônio nacional e os preceitos do novo fazer arquitetônico vinculado ao Movimento Moderno, ao qual eram adeptos. Justificando o novo a partir do primitivo, numa relação perfeita em que tudo se explica e se encaixa, a arquitetura eclética foi tratada como cópia de estilos, exacerbação de ornamentos e vinculação ao estrangeirismo, se opondo assim ao projeto de nação pleiteado. Devemos sempre rever conceitos e diretrizes, tratando de forma mais verdadeira e justa o nosso patrimônio eclético, e em consequência, nossa historiografia arquitetônica