Plant community structure mediates potential methane production and potential iron reduction in wetland mesocosms.

Abstract Wetlands are the largest natural source of methane to the atmosphere, but factors controlling methane emissions from wetlands are a major source of uncertainty in greenhouse gas budgets and projections of future climate change. We conducted a controlled outdoor mesocosm experiment to assess the effects of plant community structure (functional group richness and composition) on potential methane production and potential iron reduction in freshwater emergent marshes. Four plant functional groups (facultative annuals, obligate annuals, reeds, and tussocks) were arranged in a full-factorial design and additional mesocosms were assigned as no-plant controls. Soil samples from the top 10 cm were collected three times during the growing season to determine potential methane production and potential iron reduction (in unamended soils and in soils amended with 200 mM formate). These data were compared to soil organic matter, soil pH, and previously published data on above and belowground plant biomass. We found that functional group richness was less important than the presence of specific functional groups (reeds or tussocks) in mediating potential iron reduction. In our mesocosms, where oxidized iron was abundant and electron donors were limiting, iron reducing bacteria outcompeted methanogens, keeping methane production barely detectable in unamended lab incubations. When the possibility of re-oxidizing iron was eliminated via anaerobic incubations and the electron donor limitation was removed by adding formate, potential methane production increased and followed the same patterns as potential iron reduction. Our findings suggest that in the absence of abundant oxidized iron and/or the presence of abundant electron donors, wetlands dominated by either reeds or tussocks may have increased methane production compared to wetlands dominated by annuals. Depending on functional traits such as plant transport and rhizospheric oxygenation capacities, this could potentially lead to increased methane emissions in some wetlands. Additional research examining the role these plant functional groups play in other aspects of methane dynamics will be useful given the importance of methane as a greenhouse gas

Liver Sinusoid on a Chip: Long-Term Layered Co-Culture of Primary Rat Hepatocytes and Endothelial Cells in Microfluidic Platforms

We describe the generation of microfluidic platforms for the co-culture of primary hepatocytes and endothelial cells; these platforms mimic the architecture of a liver sinusoid. This paper describes a progressional study of creating such a liver sinusoid on a chip system. Primary rat hepatocytes (PRHs) were co-cultured with primary or established endothelial cells in layers in single and dual microchannel configurations with or without continuous perfusion. Cell viability and maintenance of hepatocyte functions were monitored and compared for diverse experimental conditions. When primary rat hepatocytes were co-cultured with immortalized bovine aortic endothelial cells (BAECs) in a dual microchannel with continuous perfusion, hepatocytes maintained their normal morphology and continued to produce urea for at least 30 days. In order to demonstrate the utility of our microfluidic liver sinusoid platform, we also performed an analysis of viral replication for the hepatotropic hepatitis B virus (HBV). HBV replication, as measured by the presence of cell-secreted HBV DNA, was successfully detected. We believe that our liver model closely mimics the in vivo liver sinusoid and supports long-term primary liver cell culture. This liver model could be extended to diverse liver biology studies and liver-related disease research such as drug induced liver toxicology, cancer research, and analysis of pathological effects and replication strategies of various hepatotropic infectious agents

Bidding process in online auctions and winning strategy:rate equation approach

Online auctions have expanded rapidly over the last decade and have become a fascinating new type of business or commercial transaction in this digital era. Here we introduce a master equation for the bidding process that takes place in online auctions. We find that the number of distinct bidders who bid $k$ times, called the $k$-frequent bidder, up to the $t$-th bidding progresses as $n_k(t)\sim tk^{-2.4}$. The successfully transmitted bidding rate by the $k$-frequent bidder is obtained as $q_k(t) \sim k^{-1.4}$, independent of $t$ for large $t$. This theoretical prediction is in agreement with empirical data. These results imply that bidding at the last moment is a rational and effective strategy to win in an eBay auction.Comment: 4 pages, 6 figure

The effect of cyclic-loading generated intergranular strains on the creep deformation of a polycrystalline material

Intergranular strains are generated due to the incompatible deformations at grain length-scales during plastic loading in a polycrystalline material. Estimating the effects of intergranular strains on the creep life of the material is of interest for accurate life prediction of high-temperature structural systems. In this study, the effect of the cyclic loading generated intergranular strains on the creep deformation behaviour of Type 316H austenitic stainless steel was studied using in-situ neutron diffraction. The load-controlled creep dwells introduced at various positions during tension-compression cyclic loading with different intergranular strain state but under the same applied stress showed markedly different behaviours. It is inferred that the intergranular strains are a significant contributor to the observed differences in creep deformation behaviour. Comparing the evolution of intergranular strains in various grain families during plastic and creep deformation, it was found that the grain families which deformed relatively more or less during plastic deformation behaved similarly during creep deformation. The present work shows that intergranular strains, which contribute to accelerating/decelerating creep deformation rates, need to be accounted for in current creep life assessment procedures, to obtain a more realistic creep deformation prediction under cyclic loading conditions

Origin of the Bauschinger effect in a polycrystalline material

There is a long and lively debate in the literature about the origin of the Bauschinger effect in polycrystalline materials, the most widely accepted explanation being the easier movement of dislocations during reverse loading causing the reduction of the yield stress. Other explanations include incompatible deformation at the grain scale and change of dislocation cell structures during forward and reverse loading, but recent publications show these phenomenological explanations of the Bauschinger effect are not holistic. In the experimental work presented here, we have investigated the role of micro residual lattice strain on the origin of the Bauschinger effect in type 316H austenitic stainless steel using in-situ neutron diffraction. Standard cylindrical specimens were tension-compression load cycled at room temperature with the loading interrupted at incrementally larger compressive and tensile strains followed by reloading to the tensile loop peak strain. Mirror symmetric compression-tension cyclic tests were also performed with tensile and compressive load interruptions followed by compressive reloading to the compressive loop peak strain. A strong correlation is demonstrated between the evolution of residual lattice strain in the grain families and the change in magnitude in macroscopic yield stress, peak stress and the shape of the yielding part of the stress-strain curve for both the cyclic tension yield and compression yield tests. This implies that the residual lattice strain generated by grain scale elastic and plastic deformation anisotropy is the primary source of the Bauschinger kinematic hardening effect observed in type 316H austenitic stainless steel

Determination of plastic properties of metals by instrumented indentation using a stochastic optimization algorithm

A novel optimization approach, capable of extracting the mechanical properties of an elasto-plastic material from indentation data, is proposed. Theoretical verification is performed on two simulated configurations. The first is based on the analysis of the load-displacement data and the topography of the residual imprint of a single conical indenter. The second is based on the load-displacement data obtained from two conical indenters with different semi-angles. In both cases, a semi-analytical approach [e.g., Dao et al., Acta Mater. 49, 3899 (2001) and Bucaille et al., Acta Mater. 51, 1663 (2003)] is used to estimate Young's modulus, yield stress, and strain hardening coefficient from the load-displacement data. An inverse finite element model, based on a commercial solver and a newly developed optimization algorithm based on a robust stochastic methodology, uses these approximate values as starting values to identify parameters with high accuracy. Both configurations use multiple data sets to extract the elastic-plastic material properties; this allows the mechanical properties of materials to be determined in a robust wa

Nuclear-spin relaxation of 207^{207}Pb in ferroelectric powders

Motivated by a recent proposal by O. P. Sushkov and co-workers to search for a P,T-violating Schiff moment of the $^{207}$Pb nucleus in a ferroelectric solid, we have carried out a high-field nuclear magnetic resonance study of the longitudinal and transverse spin relaxation of the lead nuclei from room temperature down to 10 K for powder samples of lead titanate (PT), lead zirconium titanate (PZT), and a PT monocrystal. For all powder samples and independently of temperature, transverse relaxation times were found to be $T_2\approx 1.5$ms, while the longitudinal relaxation times exhibited a temperature dependence, with $T_1$ of over an hour at the lowest temperatures, decreasing to $T_1\approx 7$s at room temperature. At high temperatures, the observed behavior is consistent with a two-phonon Raman process, while in the low temperature limit, the relaxation appears to be dominated by a single-phonon (direct) process involving magnetic impurities. This is the first study of temperature-dependent nuclear-spin relaxation in PT and PZT ferroelectrics at such low temperatures. We discuss the implications of the results for the Schiff-moment search.Comment: 6 pages, 4 figure

SU(5) Heterotic Standard Model Bundles

We construct a class of stable SU(5) bundles on an elliptically fibered Calabi-Yau threefold with two sections, a variant of the ordinary Weierstrass fibration, which admits a free involution. The bundles are invariant under the involution, solve the topological constraint imposed by the heterotic anomaly equation and give three generations of Standard Model fermions after symmetry breaking by Wilson lines of the intermediate SU(5) GUT-group to the Standard Model gauge group. Among the solutions we find some which can be perturbed to solutions of the Strominger system. Thus these solutions provide a step toward the construction of phenomenologically realistic heterotic flux compactifications via non-Kahler deformations of Calabi-Yau geometries with bundles. This particular class of solutions involves a rank two hidden sector bundle and does not require background fivebranes for anomaly cancellation.Comment: 17 page

Compact F-theory GUTs with U(1)_PQ

We construct semi-local and global realizations of SU(5) GUTs in F-theory that utilize a U(1)_PQ symmetry to protect against dimension four proton decay. Symmetries of this type, which assign charges to H_u and H_d that forbid a tree level \mu term, play an important role in scenarios for neutrino physics and gauge mediation that have been proposed in local F-theory model building. As demonstrated in arXiv:0906.4672, the presence of such a symmetry implies the existence of non-GUT exotics in the spectrum, when hypercharge flux is used to break the GUT group and to give rise to doublet-triplet splitting. These exotics are of precisely the right type to solve the unification problem in such F-theory models and might also comprise a non-standard messenger sector for gauge mediation. We present a detailed description of models with U(1)_PQ in the semi-local regime, which does not depend on details of any specific Calabi-Yau four-fold, and then specialize to the geometry of arXiv:0904.3932 to construct three-generation examples with the minimal allowed number of non-GUT exotics. Among these, we find a handful of models in which the D3-tadpole constraint can be satisfied without requiring the introduction of anti-D3-branes. Finally, because SU(5) singlets that carry U(1)_PQ charge may serve as candidate right-handed neutrinos or can be used to lift the exotics, we study their origin in compact models and motivate a conjecture for how to count their zero modes in a semi-local setting.Comment: 73 pages, 5 figures, v2: minor corrections to 4.3 and 6.3.1, reference adde