Neel Order and Electron Spectral Functions in the Two-Dimensional Hubbard Model: a Spin-Charge Rotating Frame Approach

Using recently developed quantum SU(2)xU(1) rotor approach, that provides a self-consistent treatment of the antiferromagnetic state we have performed electronic spectral function calculations for the Hubbard model on the square lattice. The collective variables for charge and spin are isolated in the form of the space-time fluctuating U(1) phase field and rotating spin quantization axis governed by the SU(2) symmetry, respectively. As a result interacting electrons appear as composite objects consisting of bare fermions with attached U(1) and SU(2) gauge fields. This allows us to write the fermion Green's function in the space-time domain as the product CP^1 propagator resulting from the SU(2) gauge fields, U(1) phase propagator and the pseudo-fermion correlation function. As a result the problem of calculating the spectral line shapes now becomes one of performing the convolution of spin, charge and pseudo-fermion Green's functions. The collective spin and charge fluctuations are governed by the effective actions that are derived from the Hubbard model for any value of the Coulomb interaction. The emergence of a sharp peak in the electron spectral function in the antiferromagnetic state indicates the decay of the electron into separate spin and charge carrying particle excitations.Comment: 16 pages, 5 figures, submitted to Phys. Rev.

Track A Basic Science

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd

Borboletas (Lepidoptera: Hesperioidea e papilionoidea) de val de serra, região central do rio grande do sul, Brasil

The butterfly fauna of the Atlantic Forest Biome is reasonably well-known up to the southern limit of its distribution. However, there are knowledge gaps nearby the central region of Rio Grande do Sul State, whose forest areas are considered priorities for biological conservation. This study investigated the butterfly assemblage of a riparian fragment in an ecotone area between Mixed Ombrophilous Forest and Seasonal Decidous Forest, in Itaara municipality. From September 2005 to September 2006, after 105 net-hours through active search sampling, 877 butterflies were registered representing 104 species. Three more species were registered posteriorly, increasing total richness to 107. The most abundant species were the Nymphalidae Hermeuptychia hermes (Fabricius, 1775), Yphthimoides celmis (Godart, [1824]), Agraulis vanillae maculosa (Stichel, [1908]), Tegosa claudina (Eschscholtz, 1821) and Vanessa braziliensis (Moore, 1883). One new record for the State and four new ones for the central region were registered besides the southern endemic Papilionidae Euryades corethrus (Boisduval, 1836) and the Lycaenidae Arcas ducalis (Westwood, 1852), considered indicator of Atlantic forest preserved areas. Due to the representativeness of the registered fauna, it is suggested the increase of conservation efforts in the area and stimulation of new ecological studies with the local biodiversity

Microesferas de alginato con Bacillus subtilis

La microencapsulación de organismos ha sido considerada como una alternativa de inmovilización de células, a fin de que éstas puedan ejercer sus funciones en forma gradual. El objetivo del presente estudio fue elaborar microesferas de Bacillus subtilis ya sea en forma esporulada como vegetativa. Microesferas de Bacillus subtilis son preparadas utilizando alginato de sodio. Algunas propiedades típicas del sistema microencapsulado, tales como contenido de microorganismos, tamaño de partícula y tiempo de germinación han sido estudiados. Las microesferas se prepararon mediante el método de coaservación-separación de fases, utilizando una etapa intermedia de emulsión múltiple. Las condiciones de preparación han sido lo suficientemente benignas para no producir cambios en las propiedades biológicas generales del sistema, pero con la protección que le otorga la matriz del hidrogel, la cual evita la directa comunicación con el medio externo. La viabilidad demostrada por las microesferas con las formas esporuladas fue significativamente superior a las de las formas vegetativas.Bacillus subtilis microspheres were prepared by using sodium alginate. Some typical properties of microencapsulated systems such as content of microorganisms, particle size and germination time were studied. Microspheres are prepared by the coacervation phase separation method, mainly based on an intermediate stage of primary emulsion. The preparation conditions were very soft to avoid changes in general biological products of calcium alginate microspheres containing cells, but giving them protection with a hydrogel matrix, without preventing the communication with the surrounding medium. The encapsulation of microbial spores and viable cells of a model microorganism (Bacillus subtilis) can be achieved by using sodium alginate in a satisfactory manner. Spore microspheres showed higher viability comparated to vegetative microspheres.The authors wish to acknowledge the support of this work provided UBACyT (01/TB12)

Fish immunity to scuticociliate parasites

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined

Reprint of "Fish immunity to scuticociliate parasites"

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this' review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined. (C) 2013 Elsevier Ltd. All rights reserved

Turbot resistance to Philasterides dicentrarchi is more dependent on humoral than on cellular immune responses

Philasterides dicentrarchi is a ciliate that causes high mortalities in cultured turbot, Psetta maxima (L.). This pathogen displays high phagocytic activity and after entering the body it multiplies and feeds on host cells and tissue components. In previous studies, we found that complement, activated through the classical pathway, is a potent killer of P. dicentrarchi. Here, we compared the killing activity of turbot leucocytes and humoral factors against two virulent isolates of P. dicentrarchi, in order to determine the importance of leucocytes in the defence against this pathogen. Components of P. dicentrarchi (ciliary and membrane) stimulated turbot leucocytes, and increased the respiratory burst, degranulation and the expression of pro-inflammatory cytokines. We tested the susceptibility of ciliates to reactive oxygen and nitrogen species, by incubating them with different oxidative systems (H2O2, Fe/ascorbate, which induces lipid peroxidation, an O2- donor (XOD/HX), an NO donor (SNAP) and an ONOO- donor (SIN-1)), for 24 h. Both isolates were susceptible to high concentrations of H2O2, Fe/ascorbate, XOD/HX, and SIN-1 but were resistant to incubation with SNAP. Leucocytes became strongly activated when they were in contact with or were phagocytosed by the ciliate. Incubation of P. dicentrarchi with a combination of fresh serum and specific antibodies killed most of the ciliates, but the addition of leucocytes to ciliate cultures did not increase the toxicity to the ciliates. On the contrary, the number of ciliates increased when leucocytes were added to the culture because the ciliates fed on them. Despite being activated, leucocytes did not produce sufficiently high concentrations of toxic substances to kill the parasite. The most virulent isolate was that which induced greatest activation of leucocytes but was least susceptible to complement. We concluded that humoral factors such as complement (activated through the classical pathway) are critical for fish defence against P. dicentrarchi and that cellular responses appear to play a minor role, if any, in defence against this ciliat

Effects of upwelling intensity on nitrogen and carbon Fluxes through the planktonic food web off A Coruña (Galicia, NW Spain) assessed with stable isotopes.

The input of new nutrients by upwelling in shelf waters, and the associated carbon and nitrogen fluxes, can be traced by their stable isotope signatures in organic matter. Here, we analyze the relationships between upwelling intensity and natural abundance of stable carbon and nitrogen isotopes in seston, sedimented particles, and four plankton size fractions (200 to 5000 µm) sampled monthly during 2010 and 2011 in a seasonal upwelling ecosystem. Upwelling modified the seasonal warming stratification by introducing cold and nutrient-rich waters in subsurface layers, enhancing chlorophyll-a and diatom abundance. Seston and sedimented particles were enriched in heavy nitrogen (but not carbon) isotopes linearly with upwelling intensity, indicating a primary effect of upwelling on phytoplankton production. In contrast, all plankton fractions were enriched in heavy carbon isotopes with upwelling, mainly due to the consumption of diatoms. These results confirm the differential effect of upwelling on nitrogen and carbon fluxes in the plankton food web. Direct effects of the new nitrogen inputs on phytoplankton are less evident with the increase of plankton size as nitrogen is repeatedly recycled, while the enriched carbon of plankton suggests the consumption of diatoms during upwelling. We provide linear equations to assess the influence of changes in upwelling intensity on nitrogen and carbon fluxes in seston and plankton in this ecosystem, as well as to estimate reference baseline values for food web studies