Phase Transition and Monopoles Densities in a Nearest Neighbors Two-Dimensional Spin Ice Model

In this work, we show that, due to the alternating orientation of the spins in the ground state of the artificial square spin ice, the influence of a set of spins at a certain distance of a reference spin decreases faster than the expected result for the long range dipolar interaction, justifying the use of the nearest neighbor two dimensional square spin ice model as an effective model. Using an extension of the model presented in ref. [Scientific Reports 5, 15875 (2015)], considering the influence of the eight nearest neighbors of each spin on the lattice, we analyze the thermodynamics of the model and study the monopoles and string densities dependence as a function of the temperature.Comment: 11 pages, 8 figure

de Broglie-Proca and Bopp-Podolsky massive photon gases in cosmology

We investigate the influence of massive photons on the evolution of the expanding universe. Two particular models for generalized electrodynamics are considered, namely de Broglie-Proca and Bopp-Podolsky electrodynamics. We obtain the equation of state (EOS) $P=P(\varepsilon)$ for each case using dispersion relations derived from both theories. The EOS are inputted into the Friedmann equations of a homogeneous and isotropic space-time to determine the cosmic scale factor $a(t)$. It is shown that the photon non-null mass does not significantly alter the result $a\propto t^{1/2}$ valid for a massless photon gas; this is true either in de Broglie-Proca's case (where the photon mass $m$ is extremely small) or in Bopp-Podolsky theory (for which $m$ is extremely large).Comment: 8 pages, 2 figures; v2 matches the published versio

Low-field microwave absorption and magnetoresistance in iron nanostructures grown by electrodeposition on n-type lightly-doped silicon substrates

In this study we investigate magnetic properties, surface morphology and crystal structure in iron nanoclusters electrodeposited on lightly-doped (100) n-type silicon substrates. Our goal is to investigate the spin injection and detection in the Fe/Si lateral structures. The samples obtained under electric percolation were characterized by magnetoresistive and magnetic resonance measurements with cycling the sweeping applied field in order to understand the spin dynamics in the as-produced samples. The observed hysteresis in the magnetic resonance spectra, plus the presence of a broad peak in the non-saturated regime confirming the low field microwave absorption (LFMA), were correlated to the peaks and slopes found in the magnetoresistance curves. The results suggest long range spin injection and detection in low resistive silicon and the magnetic resonance technique is herein introduced as a promising tool for analysis of electric contactless magnetoresistive samples.Comment: 12 pages, 5 figure

Sistematização de dados bibliográficos relacionados aos impactos ambientais da produção agrícola sobre as águas fluviais no corredor de Nacala, Moçambique.

Resumo: As atividades do bolsista foram desenvolvidas no escopo do ProSAVANA-TEC (Projeto de Melhoria da Capacidade de Pesquisa e de Transferência de Tecnologia para o Desenvolvimento da Agricultura no Corredor de Nacala em Moçambique), organizando levantamentos bibliográficos de informações disponíveis na internet sobre a qualidade da água superficial nas bacias hidrográficas localizadas na região do Corredor de Nacala e em Moçambique como um todo. A organização do material bibliográfico foi realizada por meio dos programas computacionais "ZOTERO", "MENDELEY.COM" e "MENDELEY- DESKTOP". Por fim, obteve-se uma coletânea de material bibliográfico, organizado digitalmente, para otimizar as consultas bibliográficas dos membros da equipe do ProSavana, assim como de outros interessados nos temas desta coletânea, assim facilitada pelo uso da ferramenta computacional selecionada. Abstract: The activities of the grantee have been developed within the scope of ProSavana-TEC (Project Capacity Enhancement of Research and Technology Transfer for the Development of Agriculture in the Nacala Corridor in Mozambique), organizing bibliographic information available on the internet about the surface water quality in the river basins located in the region of the Nacala Corridor as well as Mozambique as a whole. The organization of the bibliographic material was performed by the use of the softwares"Zotero", "MENDELEY.COM" and "Mendeley-DESKTOP". Finally, we obtained a collection of bibliographic material, that was digitally organized, to optimize the bibliographic queries of theProSavana team members as well as queries of other people interested in topics of this collection , which access will be facilitated by the use of the selected computational tools

Sustainability in the footwear sector in Portugal perceived by consumer habits

Today, the damages brought by the linear production system throughout history are apparent, and at this moment, the harm caused to the bio- sphere and the depletion of natural resources are perceived, as endangering the well-being and even the survival of humanity. In Portugal, the footwear sector becomes worrying due to the observed expansion of economic values and con- sequently the use of materials and resources, namely synthetic hides and leath- er. This research starts with a brief characterization of the footwear sector in Portugal, followed by a contextualization of the importance of the transition from the current production scenario to a Circular Economy. It ends with a study of consumption habits through a survey. It raises reflections on the num- ber of products purchased per user, purchase motivations, forms of disposal, and familiarization with sustainability concepts. The collected information is analyzed under the principles of sustainability and especially the concept of the circular economy, which reveals impressive results and conclusions that can be extremely useful in developing new products and services for sustainability

Citros: a podridão floral.

Introducao; Causa; Sintomas; Disseminacao; Controle; Estudo economico.bitstream/item/44463/1/CPATC-DOCUMENTOS-07-CITROS-A-PODRIDAO-FLORAL-FL-13125a.pd

Coupled quantum wires

We study a set of crossed 1D systems, which are coupled with each other via tunnelling at the crossings. We begin with the simplest case with no electron-electron interactions and find that besides the expected level splitting, bound states can emerge. Next, we include an external potential and electron-electron interactions, which are treated within the Hartree approximation. Then, we write down a formal general solution to the problem, giving additional details for the case of a symmetric external potential. Concentrating on the case of a single crossing, we were able to explain recent experinents on crossed metallic and semiconducting nanotubes [J. W. Janssen, S. G. Lemay, L. P. Kouwenhoven, and C. Dekker, Phys. Rev. B 65, 115423 (2002)], which showed the presence of localized states in the region of crossing.Comment: 11 pages, 10 figure

Efeito do acetato de chumbo sobre a reprodução de enquitreídeos (Enchytraeidae, Oligochaeta) em solo artificial tropical.

Resumo