Euclidean Supersymmetry, Twisting and Topological Sigma Models

We discuss two dimensional N-extended supersymmetry in Euclidean signature and its R-symmetry. For N=2, the R-symmetry is SO(2)\times SO(1,1), so that only an A-twist is possible. To formulate a B-twist, or to construct Euclidean N=2 models with H-flux so that the target geometry is generalised Kahler, it is necessary to work with a complexification of the sigma models. These issues are related to the obstructions to the existence of non-trivial twisted chiral superfields in Euclidean superspace.Comment: 8 page

Advancing the use of secondary inputs in geopolymer binders for sustainable cementitious composites: A review

Because of concerns over the construction industry's heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of "green" binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems. © 2011 by the authors

Comportamento de cultivares de morango em cultivo orgânico na região sul do Estado de Sergipe.

O presente trabalho teve como objetivo verificar o comportamento das cultivares de morango nas condições edafoclimáticas de Umbaúba, SE, visando à recomendação de cultivares para cultivo orgânico em Sergipe. O experimento foi conduzido no campo experimental da Embrapa Tabuleiros Costeiros localizado no Município de Umbaúba, SE no período de 27 de junho a 09 de dezembro de 2013. Foram avaliadas oito cultivares (Ara, Aromas, Camarosa, Camino Real, Monterrey, Nina, Portola e San Andréas), em delineamento experimental de blocos casualizados com oito tratamentos, quatro repetições e parcela com 30 plantas no espaçamento de 35 cm x 35 cm. Na adubação utilizou como fontes de nutrientes a torta de mamona, hiperfosfato de gafsa, sulfato de potássio, bórax, sulfato de zinco e húmus de minhoca. Irrigação por gotejamento, ?mulching? nos canteiros com plástico preto dupla face, retiradas de folhas secas e doentes e dos estolões semanalmente. Para controle de pragas e doenças foram utilizados Fortneen para o controle de pulgão, calda sulfocálcica a 1% para controle do ácaro e calda viçosa para controle de doença

Investigation of volcanic ash based geopolymers as potential building materials

Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the gel was more viscous than a similar gel formed from metakaolin. Geopolymers made from both ashes had bulk densities of 1.7-2.0 g/cm3 and water absorption values of 20-25 %. Their compressive strength values were 25-35 MPa and the bi-axial four-point flexura! strength values ranged from 14-20 MPa. These values increased by 20 % when cured for 21 d after 90 d storage. It was also found that by curing at 200-400 °C the mechanical properties increased. Scanning electron micrographs showed that with thermal curing microcrystalline phases were present along with undissolved crystalline phases. These phases remained bound to the matrix and acted as a filler for strengthening the materials. The Ca, Mg and Fe present as impurities in the volcanic ash formed some of these crystalline phases and did not form any deleterious hydroxide or carbonate phases

Superconducting and normal-state interlayer-exchange-coupling in La0.67_{0.67}Sr0.33_{0.33}MnO3{3}-YBa2_{2}Cu3_{3}O7−La_{7}-La_{0.67}SrSr_{0.33}MnO MnO{3}$ epitaxial trilayers

The issue of interlayer exchange coupling in magnetic multilayers with superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) epitaxial trilayers through resistivity, ac-susceptibility and magnetization measurements. The ferromagnetic (FM) LSMO layers possessing in-plane magnetization suppress the critical temperature (T$_{c})$ of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d$_{Y} \sim$ 50 {\AA}, $\sim$ 4 unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J$_{1}$ ($\sim$ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75 {\AA}) grows on cooling down to T$_{c}$, followed by truncation of this growth on entering the superconducting state. The coupling energy J$_{1}$ at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$ are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.Comment: Accepted for publication in Phys. Rev.

Topological Sigma Models with H-Flux

We investigate the topological theory obtained by twisting the N=(2,2) supersymmetric nonlinear sigma model with target a bihermitian space with torsion. For the special case in which the two complex structures commute, we show that the action is a Q-exact term plus a quasi-topological term. The quasi-topological term is locally given by a closed two-form which corresponds to a flat gerbe-connection and generalises the usual topological term of the A-model. Exponentiating it gives a Wilson surface, which can be regarded as a generalization of a Wilson line. This makes the quantum theory globally well-defined.Comment: 16 pages, Appendix added, the version to appear in JHE