About a class of exact string backgrounds

This model also known as chiral null model is a generalization of the gravitational wave and fundamental string background and is exact in the \a' expansion. The reduction to 4 dimensions yields a stationary IWP solution which couples to 7 gauge fields (one gravi-photon and 6 matter gauge fields) and 4 scalars. Special cases are the Taub-NUT geometry and rotating black holes. These solutions possess a T-self-dual point where the black hole becomes massless. Discussing the S-duality we show that the Taub-NUT geometry allows an S-self-dual point and that the electric black hole corresponds to a magnetic black hole or an H-monopole. We could identify the massless black hole as $N_L=0$ and confirm the H-monopole as an $N_L=1$ string states.Comment: 28 pages, latex (correction about the internal space and add references

The ins and outs of CO₂

© 2015 The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. It is difficult to distinguish influx and efflux of inorganic C in photosynthesizing tissues; this article examines what is known and where there are gaps in knowledge. Irreversible decarboxylases produce CO2, and CO2 is the substrate/product of enzymes that act as carboxylases and decarboxylases. Some irreversible carboxylases use CO2; others use HCO3-. The relative role of permeation through the lipid bilayer versus movement through CO2-selective membrane proteins in the downhill, non-energized, movement of CO2 is not clear. Passive permeation explains most CO2 entry, including terrestrial and aquatic organisms with C3 physiology and biochemistry, terrestrial C4 plants and all crassulacean acid metabolism (CAM) plants, as well as being part of some mechanisms of HCO3- use in CO2 concentrating mechanism (CCM) function, although further work is needed to test the mechanism in some cases. However, there is some evidence of active CO2 influx at the plasmalemma of algae. HCO3- active influx at the plasmalemma underlies all cyanobacterial and some algal CCMs. HCO3- can also enter some algal chloroplasts, probably as part of a CCM. The high intracellular CO2 and HCO3- pools consequent upon CCMs result in leakage involving CO2, and occasionally HCO3-. Leakage from cyanobacterial and microalgal CCMs involves up to half, but sometimes more, of the gross inorganic C entering in the CCM; leakage from terrestrial C4 plants is lower in most environments. Little is known of leakage from other organisms with CCMs, though given the leakage better-examined organisms, leakage occurs and increases the energetic cost of net carbon assimilation

Permeability of phospholipid membrane for small polar molecules determined from osmotic swelling of giant phospholipid vesicles

A method for determining permeability of phospholipid bilayer based on the osmotic swelling of micrometer-sized giant unilamellar vesicles (GUVs) is presented as an alternative to the two established techniques, dynamic light scattering on liposome suspension, and electrical measurements on planar lipid bilayers. In the described technique, an individual GUV is transferred using a micropipette from a sucrose/glucose solution into an isomolar solution containing the solute under investigation. Throughout the experiment, vesicle cross-section is monitored and recorded using a digital camera mounted on a phase-contrast microscope. Using a least-squares procedure for circle fitting, vesicle radius R is computed from the recorded images of vesicle cross-section. Two methods for determining membrane permeability from the obtained R(t) dependence are described: the first one uses the slope of R(t) for a spherical GUV, and the second one the R(t) dependence around the transition point at which a flaccid vesicle transforms into a spherical one. We demonstrate that both methods give consistent estimates for membrane permeability.Comment: 40 pages, 8 figures, to appear in Advances in Planar Lipid Membranes and Liposomes vol. 1

Avaliação da vegetação de restinga na Praia de Jurerê, Ilha de Santa Catarina, onze anos após a execução de um projeto de recuperação ambiental e comparação com vegetação remanescente contígua

TCC(graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Biológicas. Biologia.A recuperação ambiental de áreas degradadas é uma atividade recente, cujas técnicas empregadas demandam ainda aperfeiçoamento, e que necessita de metodologias apropriadas no que se refere ao monitoramento e à avaliação do progresso da recomposição da vegetação. O presente trabalho tem por objetivo avaliar uma área de vegetação de restinga localizada na Praia de Jurerê, Ilha de Santa Catarina, onze anos após a execução de um projeto de recuperação ambiental, comparando-a com áreas de vegetação remanescente contíguas. Para essa avaliação, foi realizado um levantamento florístico e um estudo quantitativo. O primeiro contemplou toda a área de estudo, enquanto o segundo ocorreu em três setores definidos na sua porção frontal ao mar, sendo um situado na área que foi recuperada e os dois outros nas áreas de vegetação remanescente adjacentes. Nestes setores foi efetuada a avaliação da cobertura vegetal e da composição florística utilizando um método adaptado a partir do método de intercepto de linha. Foi feita também a avaliação dos parâmetros galharia, resíduos antrópicos e área exposta com e sem detritos e a medição da altura das dunas. Foram encontradas 81 espécies na área de estudo pelo levantamento florístico, sendo oito exóticas à flora brasileira. Não houve diferenças expressivas entre os setores quanto à diversidade e à dominância de espécies, aspectos considerados positivos para o progresso da recuperação ambiental. A similaridade foi maior entre setores contíguos, aspecto indicativo de um aporte de espécies das áreas de vegetação remanescente para a recuperada. A medição da altura das dunas mostrou um relevo mais baixo e uniforme no setor situado na área recuperada, evidenciando uma diferença de fisionomia entre esta e as áreas de vegetação remanescente. O método de avaliação da cobertura vegetal adotado foi considerado adequado aos fins propostos no estudo e pode ser aplicável para avaliar o progresso da recomposição da vegetação em outros projetos de recuperação ambiental

Avaliação da vegetação de restinga na Praia de Jurerê, Ilha de Santa Catarina, onze anos após a execução de um projeto de recuperação ambiental e comparação com vegetação remanescente contígua Florianópolis

TCC(graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Biológicas. Biologia.Trabalho de Conclusão de Curso apresentado ao Curso de Ciências Biológicas da Universidade Federal de Santa Catarina, como requisito para a obtenção do título de Bacharel em Ciências Biológicas

Systems analysis of the CO2 concentrating mechanism in cyanobacteria

Cyanobacteria are photosynthetic bacteria with a unique CO2 concentrating mechanism (CCM), enhancing carbon fixation. Understanding the CCM requires a systems level perspective of how molecular components work together to enhance CO2 fixation. We present a mathematical model of the cyanobacterial CCM, giving the parameter regime (expression levels, catalytic rates, permeability of carboxysome shell) for efficient carbon fixation. Efficiency requires saturating the RuBisCO reaction, staying below saturation for carbonic anhydrase, and avoiding wasteful oxygenation reactions. We find selectivity at the carboxysome shell is not necessary; there is an optimal non-specific carboxysome shell permeability. We compare the efficacy of facilitated CO2 uptake, CO2 scavenging, and HCO3− transport with varying external pH. At the optimal carboxysome permeability, contributions from CO2 scavenging at the cell membrane are small. We examine the cumulative benefits of CCM spatial organization strategies: enzyme co-localization and compartmentalization. DOI: http://dx.doi.org/10.7554/eLife.02043.00

Identifying Drug Effects via Pathway Alterations using an Integer Linear Programming Optimization Formulation on Phosphoproteomic Data

Understanding the mechanisms of cell function and drug action is a major endeavor in the pharmaceutical industry. Drug effects are governed by the intrinsic properties of the drug (i.e., selectivity and potency) and the specific signaling transduction network of the host (i.e., normal vs. diseased cells). Here, we describe an unbiased, phosphoproteomicbased approach to identify drug effects by monitoring drug-induced topology alterations. With the proposed method, drug effects are investigated under several conditions on a cell-type specific signaling network. First, starting with a generic pathway made of logical gates, we build a cell-type specific map by constraining it to fit 13 key phopshoprotein signals under 55 experimental cases. Fitting is performed via a formulation as an Integer Linear Program (ILP) and solution by standard ILP solvers; a procedure that drastically outperforms previous fitting schemes. Then, knowing the cell topology, we monitor the same key phopshoprotein signals under the presence of drug and cytokines and we re-optimize the specific map to reveal the drug-induced topology alterations. To prove our case, we make a pathway map for the hepatocytic cell line HepG2 and we evaluate the effects of 4 drugs: 3 selective inhibitors for the Epidermal Growth Factor Receptor (EGFR) and a non selective drug. We confirm effects easily predictable from the drugs’ main target (i.e. EGFR inhibitors blocks the EGFR pathway) but we also uncover unanticipated effects due to either drug promiscuity or the cell’s specific topology. An interesting finding is that the selective EGFR inhibitor Gefitinib is able to inhibit signaling downstream the Interleukin-1alpha (IL-1α) pathway; an effect that cannot be extracted from binding affinity based approaches. Our method represents an unbiased approach to identify drug effects on a small to medium size pathways and is scalable to larger topologies with any type of signaling perturbations (small molecules, 3 RNAi etc). The method is a step towards a better picture of drug effects in pathways, the cornerstone in identifying the mechanisms of drug efficacy and toxicity

Solubility and Permeation of Hydrogen Sulfide in Lipid Membranes

Hydrogen sulfide (H2S) is mainly known for its toxicity but has recently been shown to be produced endogenously in mammalian tissues and to be associated with physiological regulatory functions. To better understand the role of biomembranes in modulating its biological distribution and effects; we measured the partition coefficient of H2S in models of biological membranes. The partition coefficients were found to be 2.1±0.2, 1.9±0.5 and 2.0±0.6 in n-octanol, hexane and dilauroylphosphatidylcholine liposome membranes relative to water, respectively (25°C). This two-fold higher concentration of H2S in the membrane translates into a rapid membrane permeability, Pm = 3 cm s−1. We used a mathematical model in three dimensions to gain insight into the diffusion of total sulfide in tissues. This model shows that the sphere of action of sulfide produced by a single cell expands to involve more than 200 neighboring cells, and that the resistance imposed by lipid membranes has a significant effect on the diffusional spread of sulfide at pH 7.4, increasing local concentrations. These results support the role of hydrogen sulfide as a paracrine signaling molecule and reveal advantageous pharmacokinetic properties for its therapeutic applications

Sharpey-Schafer Lecture Gas channels

The traditional dogma has been that all gases diffuse through all membranes simply by dissolving in the lipid phase of the membrane. Although this mechanism may explain how most gases move through most membranes, it is now clear that some membranes have no demonstrable gas permeability, and that at least two families of membrane proteins, the aquaporins (AQPs) and the Rhesus (Rh) proteins, can each serve as pathways for the diffusion of both CO2 and NH3. The knockout of RhCG in the renal collecting duct leads to the predicted consequences in acid–base physiology, providing a clear-cut role for at least one gas channel in the normal physiology of mammals. In our laboratory, we have found that surface-pH (pHS) transients provide a sensitive approach for detecting CO2 and NH3 movement across the cell membranes of Xenopus oocytes. Using this approach, we have found that each tested AQP and Rh protein has its own characteristic CO2/NH3 permeability ratio, which provides the first demonstration of gas selectivity by a channel. Our preliminary AQP1 data suggest that all the NH3 and less than half of the CO2 move along with H2O through the four monomeric aquapores. The majority of CO2 takes an alternative route through AQP1, possibly the central pore at the four-fold axis of symmetry. Preliminary data with two Rh proteins, bacterial AmtB and human erythroid RhAG, suggest a similar story, with all the NH3 moving through the three monomeric NH3 pores and the CO2 taking a separate route, perhaps the central pore at the three-fold axis of symmetry. The movement of different gases via different pathways is likely to underlie the gas selectivity that these channels exhibit

Photocatalytic Degradation Using TiO2 P25: A Comparative Study for Different Textile Dyes: Degradação fotocatalítica usando TiO2 P25: Um estudo comparativo para diferentes corantes têxteis

The photocatalytic degradation of textile dyes using metallic oxides has been extensively studied due to the remarkable results. This promising approach offers a more sustainable alternative for treating textile effluents contaminated with dyes and other chemicals, intending to mitigate the environmental impact caused by the textile industry. In this context, this study aimed to investigate the degradation of different classes of synthetic dyes used in industry through the heterogeneous photocatalysis process. For this purpose, TiO2 P25 dispersed in an aqueous dye medium exposed to an isolated source of artificial UV light was used. The significance of this research lies in understanding photodegradation phenomena and studying heterogeneous catalysis mechanisms applied to the degradation of textile dyes. Furthermore, the importance of sustainability in the textile industry is highlighted, emphasizing the need for new solutions to reduce waste emissions. This study contributes significantly to understanding the degradation of textile dyes through photodegradation, providing detailed information on the reaction processes and key factors influencing the efficiency of TiO2-catalyzed degradation. The results demonstrate real application potential and support sustainable strategies for treating textile effluents, aiming to reduce the environmental impact caused by dyes