Scaling and balancing carbon dioxide fluxes in a heterogeneous tundra ecosystem of the Lena River Delta

The current assessments of the carbon turnover in the Arctic tundra are subject to large uncertainties. This problem can (inter alia) be ascribed to both the general shortage of flux data from the vast and sparsely inhabited Arctic region, as well as the typically high spatiotemporal variability of carbon fluxes in tundra ecosystems. Addressing these challenges, carbon dioxide fluxes on an active flood plain situated in the Siberian Lena River Delta were studied during two growing seasons with the eddy covariance method. The footprint exhibited a heterogeneous surface, which generated mixed flux signals that could be partitioned in such a way that both respiratory loss and photosynthetic gain were obtained for each of two vegetation classes. This downscaling of the observed fluxes revealed a differing seasonality in the net uptake of bushes (−0.89 µmol m−2 s−1) and sedges (−0.38 µmol mm−2 s−1) in 2014. That discrepancy, which was concealed in the net signal, resulted from a comparatively warm spring in conjunction with an early snowmelt and a varying canopy structure. Thus, the representativeness of footprints may adversely be affected in response to prolonged unusual weather conditions. In 2015, when air temperatures on average corresponded to climatological means, both vegetation-class-specific flux rates were of similar magnitude (−0.69 µmol m−2 s−1). A comprehensive set of measures (e.g. phenocam) corroborated the reliability of the partitioned fluxes and hence confirmed the utility of flux decomposition for enhanced flux data analysis. This scrutiny encompassed insights into both the phenological dynamic of individual vegetation classes and their respective functional flux to flux driver relationships with the aid of ecophysiologically interpretable parameters. For comparison with other sites, the decomposed fluxes were employed in a vegetation class area-weighted upscaling that was based on a classified high-resolution orthomosaic of the flood plain. In this way, robust budgets that take the heterogeneous surface characteristics into account were estimated. In relation to the average sink strength of various Arctic flux sites, the flood plain constitutes a distinctly stronger carbon dioxide sink. Roughly 42 % of this net uptake, however, was on average offset by methane emissions lowering the sink strength for greenhouse gases. With growing concern about rising greenhouse gas emissions in high-latitude regions, providing robust carbon budgets from tundra ecosystems is critical in view of accelerating permafrost thaw, which can impact the global climate for centuries

Effect of dopants on thermal stability and self-diffusion in iron nitride thin films

We studied the effect of dopants (Al, Ti, Zr) on the thermal stability of iron nitride thin films prepared using a dc magnetron sputtering technique. Structure and magnetic characterization of deposited samples reveal that the thermal stability together with soft magnetic properties of iron nitride thin films get significantly improved with doping. To understand the observed results, detailed Fe and N self-diffusion measurements were performed. It was observed that N self-diffusion gets suppressed with Al doping whereas Ti or Zr doping results in somewhat faster N diffusion. On the other hand Fe self-diffusion seems to get suppressed with any dopant of which heat of nitride formation is significantly smaller than that of iron nitride. Importantly, it was observed that N self-diffusion plays only a trivial role, as compared to Fe self-diffusion, in affecting the thermal stability of iron nitride thin films. Based on the obtained results effect of dopants on self-diffusion process is discussed.Comment: 10 pages, 9 fig

A Study of Ductile Damage and Failure of Pure Copper – Part II: Analysis of the Deep Drawing Process of a Cylindrical Shell

The analysis of the stress-strain state and strain induced damage of a cylindrical shell made of copper during the process of deep drawing is presented. The stresses on the contact surface of operating tools (punch and die) are assigned implicitly, which leads to the mixed boundary-value problem. The results are obtained on the basis of the solution of the constitutive differential equations presenting plane plastic flow in curvilinear characteristic coordinates. The material functions required for the analysis of deep drawing were obtained by experimental studies of ductile damage and failure of pure copper (cf., Zapara et al., 2011). The process of deformation with discontinuities of the tangential velocities at the plastic zone boundaries is discussed. An estimate of the local strains and damage in the material is given both for the plastic zone and for its boundaries. The distributions of strains and of the damage within the wall of a finished part are determined. These distributions strongly affect the strength properties of a shell. The modeling of ductile damage in a material during deep drawing is based on experimental results and considerably extends them for a wider range of stress triaxialities. It is shown that the use of a drawing die with a cone angle of 12°...13° leads to a noticeable shift of the stress triaxialities into a range of negative values as compared to deep drawing with a die of larger angle ( 15°...18° ). The modeling reveals a smoother increase and decrease in damage of the finished part in case of the smaller cone angle as well as the absence of void coalescence. This fact is very important when manufacturing such products at high operating speeds. The obtained results in combination with similar ones from the literature can be applied to the analysis of metal forming processes with dominant tensile deformation (e.g., drawing, deep drawing, stripdrawing, ironing)

A Study of Ductile Damage and Failure of Pure Copper – Part I: Constitutive Equations and Experiments

This paper presents the results of an experimental study of ductile damage and failure of pure copper. Uniaxial tension tests were performed for specimens with different arrangements of pre-drilled micro-holes representing the simulation models of cylindrical voids. This experimental method has already been applied by a number of researchers in order to investigate the damage of metals under plastic deformation and proved to be useful for studying an evolution of damage in ductile materials in terms of local strains of both representative volume elements (RVE) and meso-elements (i.e., material unit cells with a single void). Two measures are used for the assessment of damage in the deformed material. The first one relates damage to an increase in the void volume. The second measure accounts for the damage associated with a change in the void shape. Both measures were introduced as part of a tensorial theory of damage in Zapara et al. (2008). They are based on experimental studies of damage kinetics in metallic materials under plasticity conditions. In combination with similar data from the literature the obtained results are important for the modeling of metal forming processes with dominating tensile deformation (e.g., deep-drawing, ironing, wire drawing)

Potencial de bactérias isoladas de raízes de figueira e folhelhos pirobetuminosos no controle de Meloidogyne incognita em Ficus carica cv Roxo de Valinhos.

Tese. (Doutorado em Agronomia, Área de Concentração em Fitossanidade) - Universidade Federal de Pelotas, Pelotas, 2013. Orientador Cesar Bauer Gomes, Co-orientadora Andréa Bitencourtt Moura

Plasma extravasation mediated by lipopolysaccharide-induction of kinin B1 receptors in rat tissues.

The present study was performed to: (a) evaluate the effects of kinin B1 (Sar[D-Phe8]-des-Arg9-BK; 10 nmol/kg) and B2 (bradykinin (BK); 10 nmol/kg) receptor agonists on plasma extravasation in selected rat tissues; (b) determine the contribution of a lipopolysaccharide (LPS) (100 microg/kg) to the effects triggered by B1 and B2 agonists; and (c) characterize the selectivity of B1 ([Leu8]desArg9-BK; 10 nmol/kg) and B2 (HOE 140; 10 nmol/kg) antagonists as inhibitors of this kinin-induced phenomenon. B1 and B2 agonists were shown to increase plasma extravasation in the duodenum, ileum and also in the urinary bladder of the rat. LPS pretreatment enhanced the plasma extravasation mediated only by the B1 agonist in the duodenum, ileum, trachea, main and segmentar bronchi. These effects were prevented by the B1. but not the B2 antagonist. In normal rats, the B2 antagonist inhibited the effect of B2 agonist in all the tissues analyzed. However, in LPS-treated rats, the B2 antagonist was ineffective in the urinary bladder. These results indicate that kinins induce plasma extravasation in selected rat tissues through activation of B1 and B2 receptors, and that LPS selectively enhances the kinin effect on the B1 receptor in the duodenum, ileum, trachea and main and segmentar bronchi, and may increase B1 receptor expression in these tissues

Seasonal progression of active-layer thickness dependent on microrelief

Introduction Active-layer thickness is a major factor for all physical and biological processes in permafrost soils. It is closely related to the fluxes of energy, water and carbon between permafrost landscapes and the atmosphere. Active-layer thickness is mainly driven by air temperature, but also influenced by snow cover, summer rainfall, soil properties and vegetation characteristics (Nelson et al., 1998). The typical polygonal tundra of the Lena Delta is characterised by a pronounced microrelief, which causes a high small-scale heterogeneity of soil and vegetation properties. Consequently, also the active-layer thickness varies substantially across small lateral distances of decimetres to metres. In order to up-scale results of process studies to the landscape scale, a quantification of the heterogeneity of active-layer thickness is of great interest

Spin-polarized electron transport in ferromagnet/semiconductor heterostructures: Unification of ballistic and diffusive transport

A theory of spin-polarized electron transport in ferromagnet/semiconductor heterostructures, based on a unified semiclassical description of ballistic and diffusive transport in semiconductor structures, is developed. The aim is to provide a framework for studying the interplay of spin relaxation and transport mechanism in spintronic devices. A key element of the unified description of transport inside a (nondegenerate) semiconductor is the thermoballistic current consisting of electrons which move ballistically in the electric field arising from internal and external electrostatic potentials, and which are thermalized at randomly distributed equilibration points. The ballistic component in the unified description gives rise to discontinuities in the chemical potential at the boundaries of the semiconductor, which are related to the Sharvin interface conductance. By allowing spin relaxation to occur during the ballistic motion between the equilibration points, a thermoballistic spin-polarized current and density are constructed in terms of a spin transport function. An integral equation for this function is derived for arbitrary values of the momentum and spin relaxation lengths. For field-driven transport in a homogeneous semiconductor, the integral equation can be converted into a second-order differential equation that generalizes the standard spin drift-diffusion equation. The spin polarization in ferromagnet/semiconductor heterostructures is obtained by invoking continuity of the current spin polarization and matching the spin-resolved chemical potentials on the ferromagnet sides of the interfaces. Allowance is made for spin-selective interface resistances. Examples are considered which illustrate the effects of transport mechanism and electric field.Comment: 23 pages, 8 figures, REVTEX 4; minor corrections introduced; to appear in Phys. Rev.

Elucidating the structural composition of a Fe-N-C catalyst by nuclear and electron resonance techniques

Fe–N–C catalysts are very promising materials for fuel cells and metal–air batteries. This work gives fundamental insights into the structural composition of an Fe–N–C catalyst and highlights the importance of an in‐depth characterization. By nuclear‐ and electron‐resonance techniques, we are able to show that even after mild pyrolysis and acid leaching, the catalyst contains considerable fractions of α‐iron and, surprisingly, iron oxide. Our work makes it questionable to what extent FeN4 sites can be present in Fe–N–C catalysts prepared by pyrolysis at 900 °C and above. The simulation of the iron partial density of phonon states enables the identification of three FeN4 species in our catalyst, one of them comprising a sixfold coordination with end‐on bonded oxygen as one of the axial ligands

Generalized Drude model: Unification of ballistic and diffusive electron transport

For electron transport in parallel-plane semiconducting structures, a model is developed that unifies ballistic and diffusive transport and thus generalizes the Drude model. The unified model is valid for arbitrary magnitude of the mean free path and arbitrary shape of the conduction band edge profile. Universal formulas are obtained for the current-voltage characteristic in the nondegenerate case and for the zero-bias conductance in the degenerate case, which describe in a transparent manner the interplay of ballistic and diffusive transport. The semiclassical approach is adopted, but quantum corrections allowing for tunneling are included. Examples are considered, in particular the case of chains of grains in polycrystalline or microcrystalline semiconductors with grain size comparable to, or smaller than, the mean free path. Substantial deviations of the results of the unified model from those of the ballistic thermionic-emission model and of the drift-diffusion model are found. The formulation of the model is one-dimensional, but it is argued that its results should not differ substantially from those of a fully three-dimensional treatment.Comment: 14 pages, 5 figures, REVTEX file, to appear in J. Phys.: Condens. Matte