Residue quality and N fertilizer do not influence aggregate stabilization of C and N in two tropical soils with contrasting texture

To address soil fertility decline, additions of organic resources and mineral fertilizers are often integrated in sub-Saharan African agroecosystems. Possible benefits to long-term C and N stabilization from this input management practice are, however, largely unknown. Our objectives were (1) to evaluate the effect of residue quality and mineral N on soil C and N stabilization, (2) to determine how input management and root growth interact to control this stabilization, and (3) to assess how these relationships vary with soil texture. We sampled two field trials in Kenya located at Embu, on a clayey soil, and at Machanga, on a loamy sand soil. The trials were initiated in 2002 with residue inputs of different quality (no input, high quality Tithonia diversifolia, medium quality Calliandra calothyrsus, and low quality Zea mays (maize) stover), incorporated at a rate of 4 Mg C ha⁻¹ year⁻¹ alone and in combination with 120 kg N ha⁻¹ season⁻¹ mineral fertilizer. Maize was grown in the plots each season, and a section of the plots was left uncropped. All aboveground maize residues were removed from the plots. Soil samples (0–15 cm) were collected in March 2005 to assess aggregation and C and N stabilization. The fine-textured soil at Embu was more responsive to inputs than the coarse-textured soil at Machanga. Residue additions increased macroaggregation at Embu, and cropping increased aggregation at Machanga. At Embu adding organic residue, regardless of the quality, and cropping significantly increased total soil C and N. This increase was also observed in the macroaggregate and microaggregate-within-macroaggregate fractions. Input treatments had little effect on C and N contents of the whole soil or specific fractions at Machanga. Nitrogen fertilizer additions did not significantly alter C or N content of the whole soil or specific fractions at either site. We conclude that residue quality does not affect the stabilization of soil organic C and N. Inputs of C and soil stabilization capacity are more important controls on stabilization of soil organic matter.     

Stable dye-sensitized solar cells based on organic chromophores and ionic liquid electrolyte

A series of polyene-diphenylaniline based organic dyes (coded as D5, D7, D9 and D11) have been reported for the application in ionic liquid electrolyte based dye-sensitized solar cells. The effects of substitution of organic dyes on the photovoltaic performance have been investigated, which show addition of methoxy groups on the triphenylamine donor group increases short-circuit current, open-circuit voltage and photovoltaic performance. A power conversion efficiency of 6.5% under AM 1.5 sunlight at 100 mW/cm² has been obtained with D11 dye in combination with a binary ionic liquid electrolyte, which when subjected to accelerated testing under one sun light soaking at 60 °C, the efficiency remained 90% of initial efficiency.     

使用系统总线性能计数器来测量和改善嵌入式系统的性能

了解系统总线的活动情况可帮助开发工程师显著改善嵌入式应用的性能。过去,由于嵌入式处理器缺乏复杂的软硬件结合特性,因此监测系统总线的活动情况是一项挑战性难题。在系统级了解应用程序的行为对于有效利用系统资源非常关键,这些资源包括外部存储器、DMA控制器、仲裁、系统总线互连等。     

Model-driven visualizations of constraint-based local search

Visualization is often invaluable to understand the behavior of optimization algorithms, identify their bottlenecks or pathological behaviors, and suggest remedial techniques. Yet developing visualizations is often a tedious activity requiring significant time and expertise. This paper presents a framework for the visualization of constraint-based local search (CBLS) algorithms. Given a high-level model and a declarative visualization specification, the CBLS visualizer systematically produces animations to visualize constraints and objectives, violations, and conflicts, as well as the temporal behavior of these measures. The visualization specification is declarative and typically composed of a triple (what,where,how) indicating what to display, where, and with which graphical objects. The visualizer architecture is compositional and extensible. It provides building blocks which can be assembled freely by the user and focuses almost exclusively on static aspects, the dynamic aspects being automated by the use of invariants. The paper highlights various functionalities of the visualizer and describes a blueprint for its implementation.     

Effect of Cr additions on the electrical properties of Ni–BaTiO3 ultra-thin multilayer capacitors

Multilayer ceramic capacitors based on BaTiO₃ dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the continuity of ultra-thin Ni electrodes in Ni–BaTiO₃ multilayer capacitors could be achieved. Here, the effect of the Cr addition to the nickel electrode pastes is studied with regard to the electrical properties. Low-field electrical measurements demonstrate no major differences between Cr doped Ni and undoped Ni. However, high-field measurements show a significant decrease to the total capacitor resistance. Under a critical electrical bias the conductivity significantly increases due to a Fowler–Nordheim tunneling conduction though the interfacial Schottky barrier at the dielectric–electrode interface; the onset voltage of this conduction is much lower than with the undoped nickel. Based on these results, we evaluate criteria for the selection of an appropriate refractory metal in order to improve the Ni electrode continuity.     

Bunsen section thermodynamic model for hydrogen production by the sulfur–iodine cycle

A model for the Bunsen section of the Sulfur–Iodine thermo-chemical cycle is proposed, where sulfur dioxide reacts with excess water and iodine to produce two demixing liquid aqueous phases (H₂SO₄ rich and HI rich) in equilibrium. Considering the mild temperature and pressure conditions, the UNIQUAC activity coefficient model combined with Engels' solvation model is used. The complete model is discussed, with HI solvation by water and by iodine as well as H₂SO₄ solvation by water, leading to a very high complexity with almost hundred parameters to be estimated from experimental data. Taking into account the water excess, a successful reduced model with only 15 parameters is proposed after defining new apparent species. Acids total dissociation and total H⁺ solvation by water are the main assumptions. Results show a good agreement with published experimental data between 25 °C and 120 °C.     

HIx system thermodynamic model for hydrogen production by the Sulfur–Iodine cycle

The HI_x ternary system (H₂O–HI–I₂) is the latent source of hydrogen for the Sulfur–Iodine thermo-chemical cycle. After analysis of the literature data and models, a homogeneous approach with the Peng–Robinson equation of state used for both the vapor and liquid phase fugacity calculations is proposed for the first time to describe the phase equilibrium of this system. The MHV2 mixing rule is used, with UNIQUAC activity coefficient model combined with of hydrogen iodide solvation by water. This approach is theoretically consistent for HI_x separation processes operating above HI critical temperature. Model estimation is done on selected literature vapor–liquid, liquid–liquid, vapor–liquid–liquid and solid–liquid equilibrium data for the ternary system and the three binaries subsystems. Validation is done on the remaining literature data. Results agree well with the published data, but more experimental effort is needed to improve modeling of the HI_x system.     

Design of multimaterial processed by powder metallurgy: Processing of a (steel/cemented carbides) bilayer material

A bimaterial, consisting of tough and hard layers, was designed to be processed by powder metallurgy. A materials selection software lead to choose steel and cemented carbide for the tough and hard components. To insure the interlayer compatibility, Fe was selected as base of the tough part and as binder of the hard part. The compositions and the temperature range enabling the simultaneous consolidation of the Fe base by transient liquid phase sintering and of the WC base by liquid phase sintering were defined from thermodynamics data. Experiments lead to define a treatment in two steps: presintering (1080 °C) for the partial densification of the Fe base then sintering (1280–1320 °C) to achieve densification and cohesion of the bimaterial. The sintering temperature increase provided a higher liquid fraction leading to interface cohesion but coarse porosity development. Bimaterial, with fair mechanical properties, were obtained by presintering at 1080 °C then sintering at 1280 °C.     

Dielectric and viscoelastic studies of curing epoxy-amine model systems

Summary The curing of different epoxy-amine model systems which present only gelification and/or vitrification processes has been followed with the evolution of their viscoelastic and electrical behaviours during the network formation. Some attempts are performed to correlate the significant evolution of the mechanical and electrical parameters with the physico-chemical changes of these well defined chemical systems during their hardening and complete curing.