A Bosonic Analog of a Topological Dirac Semi-Metal: Effective Theory, Neighboring Phases, and Wire Construction

We construct a bosonic analog of a two-dimensional topological Dirac Semi-Metal (DSM). The low-energy description of the most basic 2D DSM model consists of two Dirac cones at positions $\pm\mathbf{k}_0$ in momentum space. The local stability of the Dirac cones is guaranteed by a composite symmetry $Z_2^{\mathcal{TI}}$, where $\mathcal{T}$ is time-reversal and $\mathcal{I}$ is inversion. This model also exhibits interesting time-reversal and inversion symmetry breaking electromagnetic responses. In this work we construct a bosonic version by replacing each Dirac cone with a copy of the $O(4)$ Nonlinear Sigma Model (NLSM) with topological theta term and theta angle $\theta=\pm \pi$. One copy of this NLSM also describes the gapless surface termination of the 3D Bosonic Topological Insulator (BTI). We compute the time-reversal and inversion symmetry breaking electromagnetic responses for our model and show that they are twice the value one gets in the DSM case matching what one might expect from, for example, a bosonic Chern insulator. We also investigate the stability of the BSM model and find that the composite $Z_2^{\mathcal{TI}}$ symmetry again plays an important role. Along the way we clarify many aspects of the surface theory of the BTI including the electromagnetic response, the charges and statistics of vortex excitations, and the stability to symmetry-allowed perturbations. We briefly comment on the relation between the various descriptions of the $O(4)$ NLSM with $\theta=\pi$ used in this paper (a dual vortex description and a description in terms of four massless fermions) and the recently proposed dual description of the BTI surface in terms of $2+1$ dimensional Quantum Electrodynamics with two flavors of fermion ($N=2$ QED$_3$). In a set of four Appendixes we review some of the tools used in the paper, and also derive some of the more technical results.Comment: 33 pages, 4 appendixes, v2: small corrections and added references, v3: new section added (Sec. VI) and additional references. To appear in PR

Art (Portugal)

The Great War coincided with a period of great changes and conceptions as regards artistic trends. The official nomination of painter Sousa Lopes to represent Portugal in the global conflict followed the precepts of traditional history painting; however, the results reveal a limit to its realization. In turn, modernist artists distanced themselves from the war – only soldier Christiano Cruz would produce non-state-commissioned paintings from a modernist perspective that allowed a reflection on modern art and war. [Com o apoio Fundação para a Ciência e a Tecnologia - FCT]info:eu-repo/semantics/publishedVersio

Proteção e inventário das relíquias históricas e monumentos artísticos [e] obras de interesse nitidamente turístico e de embelezamento da Terra. Políticas para o património, em S. Miguel e Santa Maria, no lustro 1946-1950

O breve estudo que aqui apresento sobre o tema das políticas distritais para o património cultural, em S. Miguel e Santa Maria, no lustro 1946-1950, surgiu no âmbito da investigação que venho desenvolvendo sobre o legado testamentário feito por Maria Francisca Borges de Medeiros Dias da Câmara (1869-1945) ao Museu Carlos Machado, comummente designado como «Legado da Condessa de Cuba». Com efeito, foi ao procurar conhecer quer a constituição quer o processo de incorporação museológica deste legado, ocorrido em 1947, que procedi, entre outras, à leitura de um conjunto de livros de actas da Comissão Executiva da Junta Geral do Distrito Autónomo de Ponta Delgada, então instituição de tutela daquele museu. Para contextualização geral do tema que agora nos ocupa, recordemos o enquadramento legal do corpo administrativo que produziu a fonte documental sobre a qual incide o presente artigo. O quinquénio em análise corresponde a um período de plena vigência do regime do Estado Novo (1933-1974), encontrando-se o território português organizado em três grandes unidades administrativas: o Continente, as Ilhas Adjacentes, e as Colónias. […].Esta edição foi financiada pela Secretaria Regional do Mar, Ciência e Tecnologia do Governo Regional dos Açores (M3.3.c/Edições/002/2019) e contou com o apoio da Direção Regional da Cultura | Centro de Estudos de História do Atlântico Alberto Vieira, no âmbito do projeto de Pós- doutoramento com a referência “M3.1.a/F/003/2016” do Fundo Regional da Ciência e Tecnologia.info:eu-repo/semantics/publishedVersio

Assessment of the Stability of Passenger Ships in Coastal Navigation in Case of Lacking Ship Geometry Data

Ships should ensure safe navigation by meeting the stability norms defined by the International Maritime Organization (IMO) and determined by national maritime administrations. The fulfillment of these norms is becoming increasingly important, especially for passenger ships used for tourist excursions. Recently, the development of maritime tourism has greatly increased the demand for these ships most of which are converted fishing vessels.  The situation described in this paper pertains to Albania and most probably differs in other countries in the region and the wider area. Ships rarely have adequate technical documentation.  The Albanian Register of Shipping requires the performance of stability tests, the results of which are entered in the amended stability book to ensure the vessels’ compliance with the norms following modifications undergone and guarantee safe navigation for tourists. An examination of a variety of ship design papers helped us identify various methods and methodologies for determining approximate geometric ship elements with an acceptable degree of reliability. However, their use should be limited and reliability proven by calculating parameters such as lightship VCG, number of passengers per m2, assessing the possible range and area of navigation and weather conditions (mainly wind speed and wave forces). The calculations based on stability testing and the use of highly reliable software such as MaxSurf - Integrated Naval Architecture Software, Napa - Naval Architectural Package Autoship - Systems Operation, Orca3D – Naval Architecture Software delivered fast and reliable stability assessment results and verified conformance with the norms prescribed by the Albanian Register of Shipping

Using eye tracking to understand banner blindness and improve website design

Banners, as a form of advertising on the web, are important for businesses. Conversely customers want to navigate the site without being distracted by irrelevant or annoying ads. Design and placement of banners is not well understood and banner blindness , which occurs when users overlook the banner entirely, is what causes the ineffectiveness of the banner. This study employs eye tracking to investigate how banner background color and the banner’s relevance to users’ tasks influence banner blindness. Eye movements were collected for users performing several tasks and viewing banners in a task-free context. Different banners were counterbalanced with task order. Findings on viewing behavior and user preference based on both questionnaires and eye tracking analysis offered evidence that banner background color and relevance did not influence banner viewing behavior. Through the use of eye tracking, we attempt to identify the effectiveness of banners on a website and offer recommendations for redesign