Sensitivity of wetland methane emissions to model assumptions: application and model testing against site observations

Abstract. Methane emissions from natural wetlands and rice paddies constitute a large proportion of atmospheric methane, but the magnitude and year-to-year variation of these methane sources is still unpredictable. Here we describe and evaluate the integration of a methane biogeochemical model (CLM4Me; Riley et al., 2011) into the Community Land Model 4.0 (CLM4CN) in order to better explain spatial and temporal variations in methane emissions. We test new functions for soil pH and redox potential that impact microbial methane production in soils. We also constrain aerenchyma in plants in always-inundated areas in order to better represent wetland vegetation. Satellite inundated fraction is explicitly prescribed in the model because there are large differences between simulated fractional inundation and satellite observations. A rice paddy module is also incorporated into the model, where the fraction of land used for rice production is explicitly prescribed. The model is evaluated at the site level with vegetation cover and water table prescribed from measurements. Explicit site level evaluations of simulated methane emissions are quite different than evaluating the grid cell averaged emissions against available measurements. Using a baseline set of parameter values, our model-estimated average global wetland emissions for the period 1993–2004 were 256 Tg CH4 yr−1, and rice paddy emissions in the year 2000 were 42 Tg CH4 yr−1. Tropical wetlands contributed 201 Tg CH4 yr−1, or 78 % of the global wetland flux. Northern latitude (>50 N) systems contributed 12 Tg CH4 yr−1. We expect this latter number may be an underestimate due to the low high-latitude inundated area captured by satellites and unrealistically low high-latitude productivity and soil carbon predicted by CLM4. Sensitivity analysis showed a large range (150–346 Tg CH4 yr−1) in predicted global methane emissions. The large range was sensitive to: (1) the amount of methane transported through aerenchyma, (2) soil pH (± 100 Tg CH4 yr−1), and (3) redox inhibition (± 45 Tg CH4 yr−1).

Studies of the wetting characteristics of liquid iron on dense alumina by the X-ray sessile drop technique

In the present work, the reaction between a molten iron drop and dense alumina was studied using the X-ray sessile-drop method under different oxygen partial pressures in the gas atmosphere. The changes in contact angles between the iron drop and the alumina substrate were followed as functions of temperature and varying partial pressures of oxygen in the temperature range 1823 to 1873 K both in static and dynamic modes. The results of the contact angle measurements with pure iron in contact with dense alumina in extremely well-purified argon as well as under different oxygen partial pressures in the gas atmosphere showed good agreement with earlier measurements reported in the literature. In the dynamic mode, when argon was replaced by a CO-CO2-Ar mixture with a well-defined PO, in the gas, the contact angle showed an initial decrease followed by a period of nearly constant contact angle. At the end of this period, the length of which was a function of the P-O2 imposed, a further steep decrease in the contact angle was noticed. An intermediate layer of FeAl2O4 was detected in the scanning electron microscope (SEM) analysis of the reacted substrates. An interesting observation in the present experiments is that the iron drop moved away from the site of the reaction once the product layer covered the interface. The results are analyzed on the basis of the various forces acting on the drop.

Alloy/Oxide Equilibria in Iron--Vanadium--Oxygen and Iron--Niobium--Oxygen Systems

An experimental characterization of three-phase equilibria in Fe--V--O and Fe--Nb--O systems at 1823, 1873 and 1923K has been carried out using a solid state cell and by analysis of quenched samples. The oxygen potentials corresponding to these three-phase equilibria were monitored by a solid state cell incorporating Y sub 2 O sub 3 doped ThO sub 2 with Cr + Cr sub 2 O sub 3 as reference electrode. Similar measurements were carried out for Fe--Nb--O alloys in equilibrium with a mixture of FeNb sub 2 O sub 6 and NbO sub 2 . These measurements permit evaluation of interaction parameters (e exp V sub O = --6590/T + 2.892 and e exp Nb sub O = --4066/T + 1.502) and activity coefficients of vanadiun and niobium in dilute solution (ln gamma exp O sub V = --35 320/T + 12.68 and ln gamma sub Nb exp O = --12 386/T + 4.34) in liquid iron. The results obtained in this study resolve a number of discrepancies in thermodynamic data reported in the literature, especially regarding the activity coefficients of V and Nb and the stability ranges for V sub 2 O sub 3 and VO sub 1+x . 18 ref.--AA

State of bismuth in BaBiO3 and BaBi1-xPbxO3: Bi 4f photoemission and Bi L3 absorption spectroscopic studies

The 2p 6d feature in the Bi L3 spectra has different energies in the semiconducting (0.0≤x<0.7) and the superconducting (x=0.75) compositions of BaBi1−xPbxO3. The Bi 4f core level spectrum shows distinct features ascribable to Bi III and Bi V in BaBiO3 and in the semiconducting compositions; the width of the 4f peaks is also considerably larger in these compositions compared to that in BaBi0.25Pb0.75O3, which shows a single sharp Bi 4f feature.

Heat shock protein 90 from neglected protozoan parasites

Significant advances have been made in our understanding of heat shock protein 90 (Hsp90) in terms of its structure, biochemical characteristics, post-translational modifications, interactomes, regulation and functions. In addition to yeast as a model several new systems have now been examined including flies, worms, plants as well as mammalian cells. This review discusses themes emerging out of studies reported on Hsp90 from infectious disease causing protozoa. A common theme of sensing and responding to host cell microenvironment emerges out of analysis of Hsp90 in Malaria, Trypanosmiasis as well as Leishmaniasis. In addition to their functional roles, the potential of Hsp90 from these infectious disease causing organisms to serve as drug targets and the current status of this drug development endeavor are discussed. Finally, a unique and the only known example of a split Hsp90 gene from another disease causing protozoan Giardia lamblia and its evolutionary significance are discussed. Clearly studies on Hsp90 from protozoan parasites promise to reveal important new paradigms in Hsp90 biology while exploring its potential as an anti-infective drug target. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90). (C) 2011 Elsevier B.V. All rights reserved.

Segregation into Chiral Enantiomeric Conformations of an Achiral Molecule by Concomitant Polymorphism

An analogue of the green fluorescent protein (GFP) luminophore crystallizes from a methanol solution impregnated with dichloromethane, into a pair of chiral crystals. Thermal analysis, fluorescence emission studies, and crystal packing analysis show that the two crystals are different materials. The two polymorphs arise from the rotation of a monosubstituted benzene ring about a C-N bond which results in the formation of two strong bifurcated C-H center dot center dot center dot O intermolecular bonds to oxygen O(6). The color difference has been ascribed to a difference in the packing of the two crystal forms. Theoretical studies supported by low temperature NMR show low kinetic energy barriers (similar to 10 kJ mol(-1)) separating the asymmetric units of the two crystal structures, suggesting that the driving force for the polymorphism could be the result of packing of two different asymmetric units.

Thermo-physical and structural studies of sodium zinc borovanadate glasses in the region of high concentration of modifier oxides

This paper reports investigation of Na2O and ZnO modified borovanadate glasses in the highly modified regime of compositions. These glasses have been prepared by microwave route. Ultraviolet (UV) and visible, infrared (IR), Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) and Electron Paramagnetic Resonance (EPR) spectroscopies have been used to characterize the speciation in the glasses. Together with the variation of properties such as molar volume and glass transition temperatures, spectroscopic data indicate that at high levels of modification, ZnO tends to behave like network former. It is proposed that the observed variation of all the properties can be reasonably well understood with a structural model. The model considers that the modification and speciation in glasses are strongly determined by the hierarchy of group electronegativities. Further, it is proposed that the width of the transitions of glasses obtained under same condition reflects the fragility of the glasses. An empirical expression has been suggested to quantify fragility on the basis of width of the transition regions. (C) 2012 Elsevier Ltd. All rights reserved.

Energy Sharing for Multiple Sensor Nodes With Finite Buffers

We consider the problem of finding optimal energy sharing policies that maximize the network performance of a system comprising of multiple sensor nodes and a single energy harvesting (EH) source. Sensor nodes periodically sense the random field and generate data, which is stored in the corresponding data queues. The EH source harnesses energy from ambient energy sources and the generated energy is stored in an energy buffer. Sensor nodes receive energy for data transmission from the EH source. The EH source has to efficiently share the stored energy among the nodes to minimize the long-run average delay in data transmission. We formulate the problem of energy sharing between the nodes in the framework of average cost infinite-horizon Markov decision processes (MDPs). We develop efficient energy sharing algorithms, namely Q-learning algorithm with exploration mechanisms based on the epsilon-greedy method as well as upper confidence bound (UCB). We extend these algorithms by incorporating state and action space aggregation to tackle state-action space explosion in the MDP. We also develop a cross entropy based method that incorporates policy parameterization to find near optimal energy sharing policies. Through simulations, we show that our algorithms yield energy sharing policies that outperform the heuristic greedy method.

Insights into stabilizing interactions in the distorted domain-swapped dimer of Salmonella typhimurium survival protein

The survival protein SurE from Salmonella typhimurium (StSurE) is a dimeric protein that functions as a phosphatase. SurE dimers are formed by the swapping of a loop with a pair of beta-strands and a C-terminal helix between two protomers. In a previous study, the Asp230 and His234 residues were mutated to Ala to abolish a hydrogen bond that was thought to be crucial for C-terminal helix swapping. These mutations led to functionally inactive and distorted dimers in which the two protomers were related by a rotation of 167 degrees. New salt bridges involving Glu112 were observed in the dimeric interface of the H234A and D230A/H234A mutants. To explore the role of these salt bridges in the stability of the distorted structure, E112A, E112A/D230A, E112A/H234A, E112A/D230A/H234A, R179L/H180A/H234A and E112A/R179L/H180A/H234A mutants were constructed. X-ray crystal structures of the E112A, E112A/H234A and E112A/D230A mutants could be determined. The dimeric structures of the E112A and E112A/H234A mutants were similar to that of native SurE, while the E112A/D230A mutant had a residual rotation of 11 degrees between the B chains upon superposition of the A chains of the mutant and native dimers. The native dimeric structure was nearly restored in the E112A/H234A mutant, suggesting that the new salt bridge observed in the H234A and D230A/H234A mutants was indeed responsible for the stability of their distorted structures. Catalytic activity was also restored in these mutants, implying that appropriate dimeric organization is necessary for the activity of SurE.

Lack of Critical Slowing Down Suggests that Financial Meltdowns Are Not Critical Transitions, yet Rising Variability Could Signal Systemic Risk

Complex systems inspired analysis suggests a hypothesis that financial meltdowns are abrupt critical transitions that occur when the system reaches a tipping point. Theoretical and empirical studies on climatic and ecological dynamical systems have shown that approach to tipping points is preceded by a generic phenomenon called critical slowing down, i.e. an increasingly slow response of the system to perturbations. Therefore, it has been suggested that critical slowing down may be used as an early warning signal of imminent critical transitions. Whether financial markets exhibit critical slowing down prior to meltdowns remains unclear. Here, our analysis reveals that three major US (Dow Jones Index, S&P 500 and NASDAQ) and two European markets (DAX and FTSE) did not exhibit critical slowing down prior to major financial crashes over the last century. However, all markets showed strong trends of rising variability, quantified by time series variance and spectral function at low frequencies, prior to crashes. These results suggest that financial crashes are not critical transitions that occur in the vicinity of a tipping point. Using a simple model, we argue that financial crashes are likely to be stochastic transitions which can occur even when the system is far away from the tipping point. Specifically, we show that a gradually increasing strength of stochastic perturbations may have caused to abrupt transitions in the financial markets. Broadly, our results highlight the importance of stochastically driven abrupt transitions in real world scenarios. Our study offers rising variability as a precursor of financial meltdowns albeit with a limitation that they may signal false alarms.

Strain Rate Dependence of Plastic Flow in Ce-based Bulk Metallic Glass During Nanoindentation

The strain rate dependence of plastic deformation of Ce60Al15CU10Ni15 bulk metallic glass was studied by nanoindentation. Even though the ratio of room temperature to the glass transition temperature was very high (0.72) for this alloy, the plastic deformation was dominated by shear banding under nanoindentation. The alloy exhibited a critical loading rate dependent serrated flow feature. That is, with increasing loading rate, the alloy exhibited a transition from less prominent serrated flow to pronounced serrated flow during continuous loading but from serrated to smoother flow during stepped loading.

Micro-Scale Gas Flows

了解微尺度气体流动特点是微机电系统设计和优化的基础.有关的研究可以上溯到20世纪初Knudsen的平面槽道流动质量流量的测量和Millikan的小球阻力系数的测量,实验结果揭示了稀薄气体效应即尺度效应对气体运动的重要影响.由于流动特征长度很小,微尺度气流经常处于滑流区甚至过渡领域,流动的相似参数为Knudsen数和Mach数.因此可以考虑利用相似准则,通过增大几何尺寸、减小压力的途径,解决微机电系统实验观测遇到的困难.为解决直接模拟MonteCarlo方法分析微机电系统中低速稀薄气流遇到的统计涨落困难,我们提出了信息保存法(IP),该方法能够有效克服统计散布,并已成功用于多种微尺度气流.

Comparaciones en los patrones de crecimiento de quince poblaciones de frijol común (Phaseolus vulgaris L.) conservadas en fincas de agricultores (in situ) y ex situ

El presente estudió se llevó a cabo en la estación experimental “La compañía” con el propósito de comparar el patrón de crecimiento de 15 poblaciones locales de frijol común conservadas en fincas de agricultores y en Bancos de Germoplasma. Se consideraron tres factores de estudio con mediciones repetidas en el tiempo en un BCA con tres repeticiones. Las variables evaluadas fueron: Longitud de tallo en centímetros (cm), área foliar total en centímetros cuadrados (cm2), materia seca de láminas foliares en gramos por planta (g.p- 1 ). materia seca de restos de componentes de la planta en gramos por planta (g.p-'), materia seca total en gramos por planta (g.p-1 ) , tasa media de crecimiento absoluto en gramos por día (g.dia- 1). tasa media de crecimiento relativo en gramos por gramo presente en la planta por día (g.g- 1 día•1 índice de cosecha, y rendimiento por parcela en gramos por parcela (g. parcela-1) Las poblaciones locales y los materiales de color de semilla crema (Gualiceño) mostraron patrones de crecimiento y valores estadísticamente superiores (P< O. O 1) para longitud de tallo, área foliar y materia seca de láminas foliares al compararlas con las poblaciones almacenadas ex situ del REGEN (Nicaragua) y del CIAT (Colombia) y de color de semilla rojo o café. Sin embargo, al evaluar la materia seca total, tasa media de crecimiento absoluto y tasa media de crecimiento relativo no se registraron diferencias estadísticas significativas entre ninguno de los factores bajo estudio. Por otro lado, se apreció una interacción color por tipo de conservación estadísticamente significativa para rendimiento por parcela e índice de cosecha (P

Una investigación sobre los principios económicos de Juan Bautista Alberdi y sus vinculaciones con la tradición de la escuela austríaca

Resumen: El Dr. Juan Bautista Alberdi, abogado, jurista, periodista, tratadista de derecho comparado, constitucionalista, economista, legislador y político, es considerado una figura insoslayable en la inspiración de las instituciones políticas, sociales y económicas de la organización nacional de la República Argentina durante el siglo XIX. De hecho se lo sindica como la fuente primaria, principal y casi excluyente de la constitución de la República Argentina que fuera aprobada por el Congreso de 1853, si se toma a sus trabajos de derecho comparado,. Complementariamente, concibió un tratado sobre “El sistema económico y rentístico” que aconsejaba adoptar a la Confederación, en el cual se encuentra una gran cantidad de puntos de vista económicos que se pueden considerar muy relevantes al sistema económico a adoptar por la nación. Con posterioridad, en diferentes fechas, e incluso en forma póstuma, se dieron a conocer más trabajos suyos en los que abordaba cuestiones económicas importantes. Dada su formación, que puede considerarse anterior a la del fundador de la Escuela Austriaca, (ya que, aunque en cierto aspectos fueron contemporáneos, la vida de Alberdi se inicia y termina unos 30 años antes que la de Menger), y considerando la barrera del idioma y otras cuestiones que pueden separarlos, la idea de este trabajo es tratar de investigar sobre los puntos de contacto entre ambas corrientes del pensamiento. La intención de esta investigación es doble: Por un lado, abrir un camino de estudio y dar a conocer a otros ámbitos, el pensamiento del Genial Tucumano, y su vigencia en el tiempo. Por otro lado, y ya, de una mayor complejidad y dando lugar a mayor controversia, analizar otro aspecto. Esto es, si dada la actual revalorización del pensamiento austriaco, especialmente en lo relativo a su teoría del ciclo económico, por un lado, y la proverbial inestabilidad mostrada por la economía argentina, al menos en los últimos 80 años, se puede intentar, retornando a los valores Alberdianos rescatar un ordenamiento institucional, que por encontrarse en la esencia de su pensamiento y por ende ser absolutamente compatible con el espíritu fundacional de nuestra constitución, permita además un fortalecimiento institucional del funcionamiento económico argentino.