Real-time monitoring of proton exchange membrane fuel cell stack failure

Uneven pressure drops in a 75-cell 9.5-kWe proton exchange membrane fuel cell stack with a U-shaped flow configuration have been shown to cause localised flooding. Condensed water then leads to localised cell heating, resulting in reduced membrane durability. Upon purging of the anode manifold, the resulting mechanical strain on the membrane can lead to the formation of a pin-hole/membrane crack and a rapid decrease in open circuit voltage due to gas crossover. This failure has the potential to cascade to neighbouring cells due to the bipolar plate coupling and the current density heterogeneities arising from the pin-hole/membrane crack. Reintroduction of hydrogen after failure results in cell voltage loss propagating from the pin-hole/membrane crack location due to reactant crossover from the anode to the cathode, given that the anode pressure is higher than the cathode pressure. Through these observations, it is recommended that purging is avoided when the onset of flooding is observed to prevent irreparable damage to the stack

Spectral geometry as a probe of quantum spacetime

Employing standard results from spectral geometry, we provide strong evidence that in the classical limit the ground state of three-dimensional causal dynamical triangulations is de Sitter spacetime. This result is obtained by measuring the expectation value of the spectral dimension on the ensemble of geometries defined by these models, and comparing its large scale behaviour to that of a sphere (Euclidean de Sitter). From the same measurement we are also able to confirm the phenomenon of dynamical dimensional reduction observed in this and other approaches to quantum gravity -- the first time this has been done for three-dimensional causal dynamical triangulations. In this case, the value for the short-scale limit of the spectral dimension that we find is approximately 2. We comment on the relevance of these results for the comparison to asymptotic safety and Horava-Lifshitz gravity, among other approaches to quantum gravity.Comment: 25 pages, 6 figures. Version 2: references to figures added, acknowledgment added

Isolation and characterization of oxidizedoligogalacturonides: meccanism of dampening of damps

Oligogalacturonides (OGs) released upon partial degradation of homogalacturonan, are a well-known class of Damage-Associated Molecular Patterns (DAMPs). Besides inducing immunity, OGs negatively affect plant growth by antagonizing auxin responses. Because the recognition of DAMPs poses the intrinsic risk of activating an exaggerated response that may impair plant survival, dampening mechanisms of DAMPs should exist. Transgenic Arabidopsis plants (OGM plants) expressing a chimeric protein called "OGmachine" accumulate oligogalacturonides (OGs) in their tissues and exhibit enhanced resistance to a variety of pathogens; however the growth of these plants is severely impaired. The prolonged release of OGs triggers defense responses that in the long term are deleterious for the plant. We used the OGM plants as a tool to investigate a possible regulatory mechanism by searching for elicitor-inactive OGs that may derive from elicitor-active OGs through an enzymatic modification. By analyzing the OGs produced in the transgenic plants, modified OGs were isolated. The nature of the modification was investigated by electrospray ionization mass spectrometry and resulted to be the oxidation to galactaric acid of the residue at the reducing end of OGs (oxOGs). OxOGs were tested for their ability to induce defense responses and antagonize auxin responses. In all experiments, they were inactive as compared to the corresponding typical OGs. We succeeded to isolate and characterize one of the enzymes that causes the inactivation of OGs: it is a FAD binding oxidase, that we named OGOX1, capable of producing elicitor-inactive oxidized OGs and H2O2

K-edge X-ray absorption spectra in transition metal oxides beyond the single particle approximation: shake-up many body effects

The near edge structure (XANES) in K-edge X-ray absorption spectroscopy (XAS) is a widely used tool for studying electronic and local structure in materials. The precise interpretation of these spectra with the help of calculations is hence of prime importance, especially for the study of correlated materials which have a complicated electronic structure per se. The single particle approach, for example, has generally limited itself to the dominant dipolar cross-section. It has long been known however that effects beyond this approach should be taken into account, both due to the inadequacy of such calculations when compared to experiment and the presence of shake-up many-body satellites in core-level photoemission spectra of correlated materials. This effect should manifest itself in XANES spectra and the question is firstly how to account for it theoretically and secondly how to verify it experimentally. By using state-of-the-art first principles electronic structure calculations and 1s photoemission measurements we demonstrate that shake-up many-body effects are present in K-edge XAS dipolar spectra of NiO, CoO and CuO at all energy scales. We show that shake-up effects can be included in K-edge XAS spectra in a simple way by convoluting the single-particle first-principles calculations including core-hole effects with the 1s photoemission spectra. We thus describe all features appearing in the XAS dipolar cross-section of NiO and CoO and obtain a dramatic improvement with respect to the single-particle calculation in CuO. These materials being prototype correlated magnetic oxides, our work points to the presence of shake-up effects in K-edge XANES of most correlated transition metal compounds and shows how to account for them, paving the way to a precise understanding of their electronic structure.Comment: 6 pages, 4 picture

Adubação fosfatada e intervalo de colheita no potencial energético do resíduo da colheita da erva-mate.

O trabalho objetivou avaliar o potencial energético e o efeito da adubação fosfatada e intervalos de colheita em propriedades físicas e químicas do resíduo da colheita da erva-mate e do briquete produzido com esse. Os resíduos foram obtidos em ervais que receberam doses de 0 e 320 kg ha-1 de P 2O5, com colheitas aos 12, 18 e 24 meses. Nesses resíduos e nos briquetes (produzidos a partir da fragmentação e compactação dos resíduos) avaliaram-se as propriedades físicas e químicas. O resíduo obtido de colheita com maiores intervalos apresentou maior densidade básica e poder calorífico superior. A colheita de 18 meses gerou resíduos para produção de briquetes com maior densidade energética. Conclui-se que o resíduo da colheita da erva-mate pode ser utilizado como fonte energética e que os briquetes produzidos com este resíduo apresentam propriedades energéticas adequadas, bem como, a adubação fosfatada não afeta o poder calorífico do resíduo da erva-mate

Evidências morfológicas da ocorrência de Phaeomoniella chlamydospora em videiras no Estado do Rio Grande do Sul.

Em virtude de até o momento não ter sido relatada a ocorrência do fungo P. chlamydospora no Estado do Rio Grande do Sul, o objetivo do trabalho foi o de verificar a ocorrência do mesmo em videiras do Estado do Rio Grande do Sul, o que possibilita a geração de informações para futuras estratégias e ações de controle.bitstream/item/84833/1/Comunicado-Tecnico-134.pd

Nutrição e crescimento da erva-mate submetida à calagem.

A erva-mate ocorre naturalmente em solos ácidos, mas é comumente cultivada em consórcio com culturas anuais que requerem correção da acidez. Contudo, pouco se conhece sobre seu comportamento frente à calagem. O objetivo desse estudo foi verificar a influência do calcário no crescimento e estado nutricional de plantas jovens de erva-mate. Para isso, incubou-se o solo com 0,0, 0,7, 1,8, 2,5, 3,4, 4,3 e 5,2 g dm-3 de calcário. Após 21 dias de incubação, mudas de erva-mate foram transplantadas para vasos com 3 dm3 de solo. Após 210 dias determinou-se o crescimento em altura e diâmetro, posteriormente separou-se as plantas em folha, caule e raiz para determinação da área foliar, comprimento e volume de raízes, produção de matéria seca e teor de N, P, K, Ca, Mg, Fe, Cu, Zn, Mn e Al, além da eficiência de utilização de Ca e Mg pela planta. O solo foi analisado quimicamente. O calcário elevou os teores de Ca, Mg e K do solo e estimulou um pequeno aumento no crescimento da parte aérea das plantas, o que não ocorreu para o sistema radicular. O máximo crescimento e produção de matéria seca da parte aérea da erva-mate ocorreu em pequenas doses de calcário, quando o teor de Ca e Mg no solo se situava, respectivamente, na faixa de 3,3 a 3,4 e 1,1 a 1,4 cmolc dm-3. Nas maiores doses de calcário os teores foliares de Cu, Zn, Mn e Fe e o crescimento das plantas foram fortemente reduzidos. A eficiência de utilização de Ca e Mg pela planta reduziu com o aumento da disponibilidade dos mesmos no solo. A erva-mate mostrou ser pouco responsiva à calagem e muito tolerante ao Al. Desta forma, a aplicação de calcário deve visar o suprimento de Ca e Mg para as plantas e não a correção da acidez do solo no intuito de neutralizar o Al trocável