Time-dependent Robin boundary conditions in the dynamical Casimir effect

Motivated by experiments in which moving boundaries are simulated by time-dependent properties of static systems, we discuss the model of a massless scalar field submitted to a time-dependent Robin boundary condition (BC) at a static mirror in 1+1 dimensions. Using a perturbative approach, we compute the spectral distribution of the created particles and the total particle creation rate, considering a thermal state as the initial field state.Comment: 10 pages, 3 figures. To appear in proceedings of Conference on Quantum Field Theory under the Influence of External Condition

Cavity effects on the Fermi velocity renormalization in a graphene sheet

Recently, in the literature, it was shown that the logarithmic renormalization of the Fermi velocity in a plane graphene sheet (which, in turn, is related to the Coulombian static potential associated to electrons in the sheet) is inhibited by the presence of a single parallel conducting plate. In the present paper, we investigate the situation of a suspended graphene sheet in a cavity formed by two conducting plates parallel to the sheet. The effect of a cavity on the interaction between electrons in the graphene is not merely the addition of the effects of each plate individually. From this, one can expect that the inhibition of the renormalization of the Fermi velocity generated by a cavity is not a mere addition of the inhibition induced by each single plate. In other words, the simple addition of the result for the inhibition of the renormalization of the Fermi velocity found in the literature for a single plate could not be used to predict the exact behavior of the inhibition for the graphene between two plates. Here, we show that, in fact, this is what happens and calculate how the presence of a cavity formed by two conducting plates parallel to the suspended graphene sheet amplifies, in a non-additive manner, the inhibition of the logarithmic renormalization of the Fermi velocity. In the limits of a single plate and no plates, our formulas recover those found in the literature.This work was partially supported by the following Brazilian Agencies: Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES), Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), and Fundacao de Amparo a Pesquisa do Estado do Rio de Janeiro (FAPERJ). E. C. Marino was partially supported by CNPq and FAPERJ. D. T. Alves was partially supported by CAPES via Programa Estagio Senior no Exterior - Processo 88881.119705/2016-01, by CNPq via Processos 461826/2014-3 (Edital Universal) and 311920/2014-4 (Bolsa de Produtividade em Pesquisa), and also thanks Jaime Santos, Mikhail I. Vasilevskiy, Nuno M. R. Peres and Yuliy Bludov for useful discussions, as well as the hospitality of the Centro de Fisica, Universidade do Minho, Braga - Portugal. V. S. Alves acknowledges CNPq for support through Bolsa de Produtividade em Pesquisa n. 312654/2017-0. The authors also thank Ygor P. Silva for useful comments

Full three-dimensional isotropic carpet cloak designed by quasi-conformal transformation optics

A fully three-dimensional carpet cloak presenting invisibility in all viewing angles is theoretically demonstrated. The design is developed using transformation optics and threedimensional quasi-conformal mapping. Parametrization strategy and numerical optimization of the coordinate transformation deploying a quasi-Newton method is applied. A discussion about the minimum achievable anisotropy in the 3D transformation optics is presented. The method allows to reduce the anisotropy in the cloak and an isotropic medium could be considered. Numerical simulations confirm the strategy employed enabling the design of an isotropic reflectionless broadband carpet cloak independently of the incident light direction and polarization25192351723522CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAIS - FAPEMIGnão temnão temnão te

Nemabiome metabarcoding reveals differences between gastrointestinal nematode species infecting co-grazed sheep and goats

Our current understanding of differences in the epidemiology of gastrointestinal nematode (GIN) species in co-grazed sheep and goats is inadequate with reference to the development of sustainable control strategies. The next-generation metabarcoding sequencing method referred to as the ‘nemabiome’ allows some of these differences to be explored to describe the intensity of co-infecting GIN species. We applied this platform to study sheep and goats that were co-grazed on Guinea grass pasture in northeastern Brazil. Co-grazed goats and sheep were treated with a monepantel anthelmintic, then exposed to the same gastrointestinal nematode species. Overall, there were differences in the prevalence of GIN species identified in the sheep and goats; Trichostrongylus colubriformis and Teladorsagia circumcincta predominated in goat kids, while Haemonchus contortus predominated in adult does, ewes and lambs once burdens became re-established after anthelmintic treatment. Description of the pattern of re-infection following anthelmintic treatment was prevented by the unpredicted poor efficacy of 2.5 mg/kg and 5 mg/kg, respectively, of monepantel against O. columbianum and T. circumcincta in lambs, and T. circumcincta adult does. Differences in drug efficacy between host age and species groups may be important when considering sustainable GIN control strategies for co-grazed animals. The aggregated FECs of the adult does and goat kids representing re-established GIN burdens, were higher than those of the co-grazed adult ewes and lambs. This implies that there are inherent differences in GIN species adaptation to the two naïve small ruminant host species, and shows the need for better understanding of the factors giving rise to this situation associated with exposure to infective larvae and host responses. At the start of the study, the adult does were co-infected with several GIN species, with the highest intensity of T. circumcincta, contrasting with the situation in the adult ewes, in which H. contortus predominated. However, once burdens became re-established after treatment, H. contortus predominated in both adult does and ewes. This demonstrates the potential for host burdens of H. contortus to establish and predominate after anthelmintic treatment when burdens of co-infecting GIN species are low

Collective transport of droplets through porous media

The flow of deformable particles, such as droplets, dragged by a fluid, through a network of narrow pores inside rocks or other porous media is key in a range of applications, from enhanced oil recovery and water filtration to lab on a chip sorting of cells. The collective dynamics and its impact on the flow are poorly understood. Here, using droplets as a prototype, we show that collective transport can occur for conditions under which a single particle would get trapped at a pore channel. When a series of droplets gets trapped, the fluids flow is affected significantly, leading to an increase of the pressure difference across the pore channels, which in turn squeezes the particles through the channels. We analyze the conditions for a single droplet to flow through one pore and derive the corresponding Bond number. We also obtain a rule for the collective flow of droplets in porous media