Hidden Charge Order of Interacting Dirac Fermions on the Honeycomb Lattice

We consider the extended half-filled Hubbard model on the honeycomb lattice for second nearest neighbors interactions. Using a functional integral approach, we find that collective fluctuations suppress topological states and instead favor charge ordering, in agreement with previous numerical studies. However, we show that the critical point is not of the putative semimetal-Mott insulator variety. Due to the frustrated nature of the interactions, the ground state is described by a novel hidden {\it metallic} charge order with {\it semi-Dirac} excitations. We conjecture that this transition is not in the Gross-Neveu universality class.Comment: 5 pages, 3 figure

Albertian grammatical transformations: from the treatise to the built work in the design of sacred buildings

This paper presents a research on the use of shape grammars as an analytical tool in the history of architecture. It evolves within a broader project called Digital Alberti, whose goal is to determine the influence of De re aedificatoria treatise on Portuguese Renaissance architecture, making use of a computational framework (Krüger et al., 2011). Previous work was concerned with the development of a shape grammar for generating sacred buildings according to the rules textually described in the treatise. This work describes the transformation of the treatise grammar into another grammar that can also account for the generation of Alberti’s built work. architecture.Fundação para a Ciência e a Tecnologia (FCT)This work is funded by FEDER Grants through COMPETE – Programa Operacional Factores de Competitividade and by National Grants through FCT – Fundação para a Ciência e a Tecnologia, as part of the “Digital Alberti” project (PTDC/ AUR-AQI/108274/2008 – FCOMP-01-0124-FEDER- 008842). The project is hosted by CES at the University of Coimbra and coordinated by Mário Krüger. Bruno Figueiredo is funded by FCT with PhD grant DFRH -SFRH/BD/69910/2010

Quantum Criticality of Semi-Dirac Fermions in 2+1 Dimensions

Two-dimensional semi-Dirac fermions are quasiparticles that disperse linearly in one direction and quadratically in the other. We investigate instabilities of semi-Dirac fermions towards charge, spin-density wave and superconducting orders, driven by short-range interactions. We analyze the critical behavior of the Yukawa theories for the different order parameters using Wilson momentum shell RG. We generalize to a large number $N_f$ of fermion flavors to achieve analytic control in 2+1 dimensions and calculate critical exponents at one-loop order, systematically including $1/N_f$ corrections. The latter depend on the specific form of the bosonic infrared propagator in 2+1 dimensions, which needs to be included to regularize divergencies. The $1/N_f$ corrections are surprisingly small, suggesting that the expansion is well controlled in the physical dimension. The order-parameter correlations inherit the electronic anisotropy of the semi-Dirac fermions, leading to correlation lengths that diverge along the spatial directions with distinct exponents, even at the mean-field level. We conjecture that the proximity to the critical point may stabilize novel modulated order phases.Comment: 10, pages, 4 figures, 1 tabl

An NMR Study of a 300-kDa AAA+ Unfoldase

AAA+ ATPases are ubiquitous hexameric unfoldases acting in cellular protein quality control. In complex with proteases, they form protein degradation machinery (the proteasome) in both archaea and eukaryotes. Here, we use solution-state NMR spectroscopy to determine the symmetry properties of the archaeal PAN AAA+ unfoldase and gain insights into its functional mechanism. PAN consists of three folded domains: the coiled-coil (CC), OB and ATPase domains. We find that full-length PAN assembles into a hexamer with C2 symmetry, and that this symmetry extends over the CC, OB and ATPase domains. The NMR data, collected in the absence of substrate, are incompatible with the spiral staircase structure observed in electron-microscopy studies of archaeal PAN in the presence of substrate and in electron-microscopy studies of eukaryotic unfoldases both in the presence and in the absence of substrate. Based on the C2 symmetry revealed by NMR spectroscopy in solution, we propose that archaeal ATPases are flexible enzymes, which can adopt distinct conformations in different conditions. This study reaffirms the importance of studying dynamic systems in solution

A real-time analysis of GFP unfolding by the AAA+ unfoldase PAN

Protein quality control systems are essential to maintain a healthy proteome. They often consist of an unfoldase unit, typically an AAA+ ATPase, coupled with a protease unit. In all kingdoms of life, they function to eliminate misfolded proteins, and thus prevent that their aggregates do harm to the cell, and to rapidly regulate protein levels in the presence of environmental changes. Despite the huge progress made in the past two decades in understanding the mechanism of function of protein degradation systems, the fate of the substrate during the unfolding and proteolytic processes remains poorly understood. Here we exploit an NMR-based approach to monitor GFP processing by the archaeal PAN unfoldase and the PAN–20S degradation system in real time. We find that PAN-dependent unfolding of GFP does not involve the release of partially-folded GFP molecules resulting from futile unfolding attempts. In contrast, once stably engaged with PAN, GFP molecules are efficiently transferred to the proteolytic chamber of the 20S subunit, despite the only weak affinity of PAN for the 20S subunit in the absence of substrate. This is essential to guarantee that unfolded but not proteolyzed proteins are not released into solution, where they would form toxic aggregates. The results of our studies are in good agreement with previous results derived from real-time small-angle-neutron-scattering experiments and have the advantage of allowing the investigation of substrates and products at amino-acid resolution

Chondrogenic differentiation of human subchondral progenitor cells is affected by synovial fluid from donors with osteoarthritis or rheumatoid arthritis

<p>Abstract</p> <p>Background</p> <p>Microfracture is a first-line treatment option for cartilage repair. In microfracture, subchondral mesenchymal cortico-spongious progenitor cells (CSP) enter the defect and form cartilage repair tissue. The aim of our study was to investigate the effects of joint disease conditions on the <it>in vitro </it>chondrogenesis of human CSP.</p> <p>Methods</p> <p>CSP were harvested from the subchondral bone marrow. CSP characterization was performed by analysis of cell surface antigen pattern and by assessing the chondrogenic, osteogenic and adipogenic differentiation potential, histologically. To assess the effect of synovial fluid (SF) on chondrogenesis of CSP, micro-masses were stimulated with SF from healthy (ND), osteoarthritis (OA) and rheumatoid arthritis donors (RA) without transforming growth factor beta 3.</p> <p>Results</p> <p>CSP showed the typical cell surface antigen pattern known from mesenchymal stem cells and were capable of osteogenic, adipogenic and chondrogenic differentiation. In micro-masses stimulated with SF, histological staining as well as gene expression analysis of typical chondrogenic marker genes showed that SF from ND and OA induced the chondrogenic marker genes aggrecan, types II and IX collagen, cartilage oligomeric matrix protein (COMP) and link protein, compared to controls not treated with SF. In contrast, the supplementation with SF from RA donors decreased the expression of aggrecan, type II collagen, COMP and link protein, compared to CSP treated with SF from ND or OA.</p> <p>Conclusion</p> <p>These results suggest that in RA, SF may impair cartilage repair by subchondral mesenchymal progenitor cells in microfracture, while in OA, SF may has no negative, but a delaying effect on the cartilage matrix formation.</p

Validación por expertos del Índice de Distrés Peri-traumático relacionado con la Enfermedad por Coronavirus 2019 para su uso en el Perú.

Objectives: To perform an expert validation study of COVID-19 Peritraumatic Distress Index (CPDI) for its eventual use in Perú. Material and Methods: In a first round by experts, the CPDI was translated into Spanish and then adapted. In a second round, (n = 13), the content validity was evaluated by using Aiken’s V (V). The V was calculated for each item, as well as for the whole instrument (VTOT). Results: Of the 24 original items, only one (S7) presented non-significant values for content validity, reason for which it was removed. The final 23-items scale did not present any alterations for the VTOT calculation Conclusions: On the basis of its adequate content validity, the Spanish version of CPDI is suitable for its application in the Peruvian population. The psychometric characteristics of the instrument, as well as its proposed modification remain to be defined through quantitative studies of the construct validity.Objetivo: Efectuar una validación de contenido por expertos del Índice de Distrés Peri-traumático relacionado a COVID-19 (CPDI) para su uso en el Perú. Material y Métodos: El CPDI fue traducido al castellano y luego adaptado en una primera ronda de expertos. En una segunda ronda (n = 13), se evaluó la validez del contenido mediante el uso de la V de Aiken (V). Se calculó la V para cada ítem, así como para el instrumento en su conjunto (V TOT). Resultados: De los 24 ítems originales, solo un ítem (S7) presentó valores no significativos para validez de Objetivo: Efectuar una validación de contenido por expertos del Índice de Distrés Peri-traumático relacionado a COVID-19 (CPDI) para su uso en el Perú. Material y Métodos: El CPDI fue traducido al castellano y luego adaptado en una primera ronda de expertos. En una segunda ronda (n = 13), se evaluó la validez del contenido mediante el uso de la V de Aiken (V). Se calculó la V para cada ítem, así como para el instrumento en su conjunto (V TOT). Resultados: De los 24 ítems originales, solo un ítem (S7) presentó valores no significativos para validez de contenido, razón por la que fue eliminado. La escala con 23 ítems no presentó alteraciones en el cálculo de la VTOT. Conclusiones: Sobre la base de su validez de contenido, el CPDI en castellano es adecuado para su aplicación en n la población peruana. Quedan por definirse las características psicométricas así como la modificación propuesta del instrumento, mediante estudios cuantitativos en torno a la validez del constructo

O REGIME ADUANEIRO ESPECIAL DE DRAWBACK COMO UM INSTRUMENTO ESTRATÉGICO DE COMPETITIVIDADE PARA A REDUÇÃO DE CUSTOS

Nesta pesquisa objetivou-se analisar a viabilidade de adesão ao regime especial de Drawback como redutor de custos em um frigorífico de bovinos. Para atender o objetivo estipulado, especificamente, buscou-se identificar os requisitos necessários para adesão ao Drawback, comparar o resultado da tributação tradicional com a adoção do Drawback, verificar a adequabilidade do uso e demonstrar a viabilidade ou não da utilização do regime especial de Drawback. O referencial teórico foi ancorado na legislação tributária nacional e na gestão de custos. Em relação aos procedimentos metodológicos a pesquisa é aplicada, com abordagem essencialmente qualitativa e descritiva. A obtenção dos dados se deu por meio de pesquisa documental e de entrevistas semiestruturadas. A análise dos dados foi realizada inicialmente por análise documental, seguida da análise de conteúdo categorial que resultou em categorias como viabilidade, vantagens e dificuldades. Os resultados documentais mostraram que o Drawback efetivamente reduz a carga tributária dos insumos de exportação no frigorífico pesquisado. Concomitantemente, os resultados categoriais evidenciaram aumento do fluxo de caixa e redução dos custos, no entanto, dificuldades como o desconhecimento sobre o regime e as exigências de operacionalização dificultam a sua adesão. A partir da triangulação dos dados documentais com a análise de conteúdo concluiu-se que a adesão ao Drawback para o frigorífico pesquisado é viável. O estudo contribui para a tomada de decisão, demonstrando o Drawback como uma possibilidade de redução de custos e acarretando em maior competitividade no mercado exterior, servindo de base para posteriores pesquisas.

Re-structuring of marine communities exposed to environmental change

Species richness is the most commonly used but controversial biodiversity metric in studies on aspects of community stability such as structural composition or productivity. The apparent ambiguity of theoretical and experimental findings may in part be due to experimental shortcomings and/or heterogeneity of scales and methods in earlier studies. This has led to an urgent call for improved and more realistic experiments. In a series of experiments replicated at a global scale we translocated several hundred marine hard bottom communities to new environments simulating a rapid but moderate environmental change. Subsequently, we measured their rate of compositional change (re-structuring) which in the great majority of cases represented a compositional convergence towards local communities. Re-structuring is driven by mortality of community components (original species) and establishment of new species in the changed environmental context. The rate of this re-structuring was then related to various system properties. We show that availability of free substratum relates negatively while taxon richness relates positively to structural persistence (i.e., no or slow re-structuring). Thus, when faced with environmental change, taxon-rich communities retain their original composition longer than taxon-poor communities. The effect of taxon richness, however, interacts with another aspect of diversity, functional richness. Indeed, taxon richness relates positively to persistence in functionally depauperate communities, but not in functionally diverse communities. The interaction between taxonomic and functional diversity with regard to the behaviour of communities exposed to environmental stress may help understand some of the seemingly contrasting findings of past research