Effects of conservation tillage,crop residue and cropping systems on changes in soil organic matter and maize–legume production: a case study in Teso District

The effects of conservation tillage, crop residue and cropping systems on the changes in soil organic matter (SOM) and overall maize–legume production were investigated in western Kenya. The experiment was a split-split plot design with three replicates with crop residue management as main plots, cropping systems as sub-plots and nutrient levels as sub-sub plots. Nitrogen was applied in each treatment at two rates (0 and 60 kg N ha⁻¹). Phosphorus was applied at 60 kg P/ha in all plots except two intercropped plots. Inorganic fertilizer (N and P) showed significant effects on yields with plots receiving 60 kg P ha⁻¹ + 60 kg N ha⁻¹ giving higher yields of 5.23 t ha⁻¹ compared to control plots whose yields were as low as 1.8 t ha⁻¹ during the third season. Crop residues had an additive effect on crop production, soil organic carbon and soil total nitrogen. Crop rotation gave higher yields hence an attractive option to farmers. Long-term studies are needed to show the effects of crop residue, cropping systems and nutrient input on sustainability of SOM and crop productivity.     

Experimental study of power consumption,local characteristics distributions and homogenization energy in gas–liquid stirred tank reactors

In this paper, the power consumption, the vertical local void fraction and the local gas–liquid interfacial area are investigated in the aerated stirred tank reactors(STRs) equipped with a rigid-flexible impeller. Meanwhile, the regressive correlation based on power consumption and interfacial area is proposed. Then a novel homogenization energy(HE = RSDPtm) expression based on power consumption and local interfacial area is redefined and used to indicate the mixing efficiency. The optimal operating mode is selected based on the change of the HE value. This paper can provide research ideas for structural optimization of stirred reactors.     

Atomistic thermodynamics study of the adsorption and the effects of water–gas shift reactants on Cu catalysts under reaction conditions

Density-functional theory (DFT) calculations were performed to determine the structure and stability of oxygen, carbon monoxide and sulfur adsorption on Cu(111), (100) and (110) surfaces that are in equilibrium with a water–gas shift (WGS) reactive environment of H₂, H₂S, H₂O and CO. An atomistic thermodynamic framework based on DFT was used for describing the phase behaviors of the adsorbates on different Cu facets. Phase diagrams of each possible adsorbate on each surface were constructed as a function of the corresponding chemical potential which showed sulfur poisoning occurs even at ppm levels of H₂S in the environment at low temperatures. Under reaction conditions relevant to WGS at low temperature, CO and S adsorbed surface structures were found to be more stable then the clean catalyst surfaces. At high temperatures and high hydrogen pressures, a poisoned surface can be regenerated back to a clean surface. The shapes of a Cu nanoparticle in the WGS reaction conditions under various sulfur chemical potentials were determined using the Wulff construction. We found that the crystal shape changes significantly from one dominated by (111) and (100) facets at very low sulfur chemical potentials to a shape dominated by (110) facets at higher sulfur chemical potentials, suggesting that reactive site distributions may change under reaction conditions.     

Stability and growth of gas hydrates below the ice–hydrate–gas equilibrium line on the P–T phase diagram

Using a previously developed experimental technique, the behavior of small methane and propane hydrate samples formed from water droplets between 0.25 and 2.5 mm in size has been studied in the pressure–temperature area between the ice–hydrate–gas equilibrium line and the supercooled water–hydrate–gas metastable equilibrium line, where ice is a stable phase. The unusual persistence of the hydrates within the area bounded by these lines and the isotherms at T=253 K for methane hydrate or at T=263 K for propane hydrates was observed. This behavior has not previously been reported. For example, in the experiment carried out at 1.9 MPa and 268 K, the methane hydrates existed in a metastable state (the equilibrium pressure at 268 K is 2.17 MPa) for 2 weeks, then immediately dissociated into liquid supercooled water and gas after the pressure was isothermally decreased slightly below the supercooled water–hydrate–gas metastable equilibrium pressure. It was found that dissociation of metastable hydrate into supercooled water and gas was reversible. The lateral hydrate film growth rates of metastable methane and propane hydrates on the surface of supercooled water at a pressure below the ice–hydrate–gas equilibrium pressure were measured. The temperature range within which supercooled water formed during hydrate dissociation can exist and a role of supercooled water in hydrate self-preservation is discussed.     

Tillage and residue management effects on soil carbon and CO<Subscript>2</Subscript> emission in a wheat–corn double-cropping system

The mitigation of CO₂ emission into the atmosphere is important and any information on how to implement adjustments to agricultural practices and improve soil organic matter (SOM) stock would be helpful. We studied the effect of tillage and residue management on soil carbon sequestration and CO₂ emissions in loam soil cropped in a winter wheat–corn rotation in northern China. There were five treatments: mouldboard ploughing, rotary tillage and no-tillage with chopped residues (MC, RC and NC), additional no-tillage with whole residue (NW) and mouldboard ploughing without residue (CK). After 5 years of each tillage system, MC and RC had higher annual CO₂ efflux from soil. The CO₂ effluxes were correlated with the ratio of dissolved organic carbon to soil microbial biomass (DOC/MBC) among treatments. This effect may be due to less immobilization of soil carbon by microorganisms under long-time intensive tillage. Although both MBC and DOC showed seasonal variability, when averaged across the sampling period only MBC discriminated between treatments. After 5 years of tillage, all treatments except CK increased SOM (0.16–0.99 Mg C ha⁻¹ year⁻¹) at 0–30 cm depth and NC was the greatest, resulting from historical SOM depletion and large C return from recent residues. Despite the lowest CO₂ flux being from the NW treatment, lower input residue from decreased biomass may have lowered C sequestration. To improve soil C sequestration in rotations, the input of residue and the CO₂ emission should be balanced by adopting appropriate tillage and residue management.     

Effect of the injection-nozzle geometry on the interaction between a gas–liquid jet and a gas–solid fluidized bed

In industrial fluid cokers, bitumen is first mixed with steam in a premixer, and then fed to the atomization nozzle. The objective of this work was to evaluate the impact of both the premixer and the nozzle geometrical configuration on the quality of the liquid–solid contact resulting from injections of liquid into a gas–solid fluidized bed. To assess the quality of the liquid–solid contact a method based on electric conductance measurements of the bed material previously developed by the authors [9] was used. Liquid atomization efficiency in open air, spray geometry, and spray stability were also characterized to evaluate their effects on the nozzle spraying performance within the fluidized bed. This study indicated that spray stability is highly beneficial to the liquid–solid contact efficiency. In particular, fluid constrictions such as the series of converging and diverging sections within the nozzle have a stabilizing effect on the spray. Future optimization of the existing liquid-injection systems should consider alternative gas–liquid premixers and nozzle geometries to enhance the jet stability.     

Influence of solvent,Lewis acid–base complex,and nanoparticles on the morphology and gas separation properties of polysulfone membranes

A series of polysulfone (PSF) membranes were prepared using different solvents: dimethylformamide (DMF), tetrahydrofuran, dimethylacetamide, and n-methyl-2-pyrrolidone (NMP). The PSF membrane prepared by NMP showed the highest gas permeability. The influence of propionic acid as a Lewis acid on gas separation properties of the PSF was explored. The PSF membrane prepared by the casting solution containing 25 wt% PSF, 35 wt% propionic acid, and 40 wt% NMP showed a superior gas separation performance. The gas permeation measurements indicated that incorporating 30 wt% γ-alumina nanoparticles into the PSF matrix resulted in about the respective 43% and 41% increase in CO₂ and O₂ permeability together with a rise in CO₂/CH₄ and O₂/N₂ selectivities (13% and 7%, respectively). Furthermore, by rearranged modified Maxwell model, the role and nature of the interfacial layer in the PSF-based mixed matrix membranes were mathematically analyzed considering a reduced permeability factor.     

Influence of mono- and triple (Cr–La–Ba) doping on the mechanical,optical and gas diffusion properties of corundum

The effect of triple doping with chromium, lanthanum and barium on the mechanical, degassing and gas diffusion properties of fine-crystalline corundum synthesized in a supercritical water fluid was studied. The influence of chromium monodoping on the mechanical and optical properties of fine-crystalline corundum was also investigated. It was found that even small amounts of dopants of lanthanum and chromium during triple and monodoping of corundum significantly improve its mechanical properties (increase the abrasive ability) and reduce it several times the content of volatile gas-liquid impurities, which contributes to increase transparency of the resulting ceramics. The role of the interaction of a chromium impurity with oxygen vacancies in corundum on the increase in the static strength of crystals was suggested. The diffusion coefficients of water in doped corundum were determined. Comparison of the degassing and diffusion properties of corundum doped with La, Cr, Ba with undoped corundum and corundum doped with lanthanum was carried out. The results obtained contribute to the creation of new materials based on doped corundum with high abrasive, luminescent, and gas diffusion characteristics.     

Study of the influence of a boric–sorbitol complex on Zn–Mn electrodeposition and on the morphology, chemical composition, and structure of the deposits

Zn–Mn electrodeposition onto Pt from an electrolyte containing boric–sorbitol complex (BSC) or boric acid alone (BA) was studied. The influence of BA or BSC content on the deposition process was investigated by cyclic voltammetry and electrodeposits, produced potentiostatically, were analysed by SEM, EDX, and XRD. The voltammetric studies indicated that an increase in the BSC concentration led to a decrease in the deposition current density. EDX analysis of deposits obtained at −1.60 V showed that increasing the BA or BSC concentration in the bath induced a fall in the Mn content of the electrodeposit and that for BSC this decrease was more significant. SEM images showed that the Zn–Mn electrodeposit obtained in the presence of 0.24 M BSC were smoother than other deposits; hence, BSC acted as a grain refiner at this concentration. XRD analysis of this deposit indicated that it was composed of Zn, Mn, MnZn₁₃, and MnH_0.8.     

The effect of moisture on the failure locus and fracture energy of an epoxy–steel interface

Experimental studies have been undertaken that provide the fracture energy of an epoxy-steel interface that has been exposed to various uptake levels of moisture. The test configuration used for these studies is the mixed mode flexure (MMF) test. The specimens have been exposed to the moist environment as open-faced specimens. The results provided by the test show a steady degradation in the interface fracture energy with increasing moisture content. Surface characterisation techniques such as X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were used to characterise the nature of the failure surfaces. Both of these analyses show a reduction of adhesive fragments and carbon overlayer thickness on the steel fracture surface with increasing moisture levels. The variation of carbon overlayer thickness with moisture exhibits a similar trend as the fracture energy, indicating that the two may be related.     

Electroless nickel–phosphorus deposition on carbon steel CK-75 and study of the effects of some parameters on properties of the deposits

Electroless nickel–phosphorus (Ni–P) deposition provides coatings with high hardness and excellent resistance to wear and abrasion. In this study, autocatalytic deposition of Ni–P alloy has been carried out on steel CK-75 sheets from bath containing nickel sulfate hexahydrate, sodium hypophosphite hydrate, thiourea, lactic acid, and sodium acetate. The effects of lactic acid concentration, pH and temperature on deposition rate, composition of deposits, and hardness have been studied. Also the changes in the hardness and structure of deposits by heat-treatment were studied by X-ray diffraction and scanning electron microscopy methods. It is shown that deposits crystallized after heat-treatment at 400°C for 1 h and crystallization to Ni and Ni₃P was observed.     

Model for seawater fouling and effects of temperature,flow velocity and surface free energy on seawater fouling☆

A kinetic model was proposed to predict the seawater fouling process in the seawater heat exchangers.The new model adopted an expression combining depositional and removal behaviors for seawater fouling based on the Kern–Seaton model.The present model parameters include the integrated kinetic rate of deposition(k d)and the integrated kinetic rate of removal(k r),which have clear physical signi ficance.A seawater-fouling monitoring device was established to validate the model.The experimental data were well fitted to the model,and the parameters were obtained in different conditions.SEM and EDX analyses were performed after the experiments,and the results show that the main components of seawater fouling are magnesium hydroxide and aluminum hydroxide.The effects of surface temperature,flow velocity and surface free energy were assessed by the model and the experimental data.The results indicate that the seawater fouling becomes aggravated as the surface temperature increased in a certain range,and the seawater fouling resistance reduced as the flow velocity of seawater increased.Furthermore,the effect of the surface free energy of metals was analyzed,showing that the lower surface free energy mitigates the seawater fouling accumulation.     

Influences of crystallization temperature on the structure,dielectric, and energy storage characteristics of KBaSrNb5O15-based glass–ceramics

Glass–ceramics capacitors have great application potential in pulsed power systems, due to ultrafast discharge speed and high dielectric breakdown strength (BDS). Here, lead-free niobate glass–ceramic dielectric materials were synthesized, and the effects of heat treatment temperature on the dielectric, ferroelectric, and energy storage properties of glass–ceramics were investigated comprehensively. The results exhibit that the dielectric permittivity first increases and then decreases as the crystallinity increases; however, the dielectric BDS diminishes. At the optimum crystallization temperature of 740°C, the maximum value of discharge energy density is 2.2 J/cm³ at 600 kV/cm, which is about 7.6 times that of mother glass. Furthermore, an ultrahigh power density of about 380.9 MW/cm³ and ultrafast discharge speed of about 11.2 ns were achieved simultaneously. Meanwhile, great thermal stability of charge–discharge property was verified in this glass–ceramics. According to P–E loops and dielectric test result, a high dielectric constant (∼207) and low dielectric loss (<0.005) as well as high energy storage efficiency of about 94.9% were achieved for G740 sample. The previous results make the obtained glass–ceramic as potential candidates in dielectric capacitors.     

Synthesis of hybrid compounds apatite–alendronate by reactive milling and effects on the structure and morphology of the apatite phase

The preparation of apatite–alendronate hybrid materials by reactive milling is proposed in this work. Calcium phosphate compounds of various compositions have been associated to bisphosphonates and found suitable for local application with release kinetics of the drug compatible with the inhibition of bone resorption. Hybrid compounds have been obtained by reactive milling. The compositions used were: AP(X-100), Alendronate(X) where X=7 and X=15. An interaction between the hydroxyl group of the apatite and the amine group of alendronate can be identified with FTIR and enables to confirm the formation of the hybrids. The incorporation of the alendronate hinders the growing of the apatite crystals resulting in smaller coherent domains of diffraction for the apatite phase.     

The effects of promoters on catalytic properties and deactivation–regeneration of the catalyst in the synthesis of dimethyl carbonate

The effects of different alkali metal promoters in PdCl₂-CuCl₂/activated carbon (a.c.) catalyst on the reaction performance for synthesizing dimethyl carbonate (DMC) by gas-phase oxidative carbonylation of methanol were studied. The bulk and surface properties of catalyst PdCl₂-CuCl₂-CH₃COOK/a.c. were characterized by XRD, XPS, and AAS techniques. On the basis of catalyst characterization and activity evaluation, the functions of promoters were further investigated, and the deactivation–regeneration of catalyst PdCl₂-CuCl₂-CH₃COOK/a.c. was also discussed. The results show that the space time yield (STY) of DMC on catalysts with different alkali metal promoters ranks in the following order: K>Na>Li. The main reason for catalyst deactivation is the loss of chlorine. Fortunately, during the preparation of the catalyst, the interaction between CH₃COOK and PdCl₂ or CuCl₂ that results in the formation of KCl limits the loss of chlorine. An obvious increase of the catalyst lifetime and catalytic activity is observed by treating fresh catalyst with a methanol solution of methyl chloroacetate. If deactivated catalyst is treated with a methanol solution of methyl chloroacetate in N₂ stream at 200 °C for 4 h and then treated in N₂ stream at 200 °C for 2 h, the catalytic activity can be restored effectively and the regeneration induction period can be shortened. The catalytic activity after two times of regeneration can still be restored to 93% of the fresh catalyst. The run time of this catalyst is up to 300 h.     

Effects of Zn, Cu, and K Promoters on the Structure and on the Reduction, Carburization, and Catalytic Behavior of Iron-Based Fischer–Tropsch Synthesis Catalysts

Zn, K, and Cu effects on the structure and surface area and on the reduction, carburization, and catalytic behavior of Fe–Zn and Fe oxides used as precursors to Fischer–Tropsch synthesis (FTS) catalysts, were examined using X-ray diffraction, kinetic studies of their reactions with H₂ or CO, and FTS reaction rate measurements. Fe₂O₃ precursors initially reduce to Fe₃O₄ and then to metallic Fe (in H₂) or to a mixture of Fe_2.5C and Fe₃C (in CO). Zn, present as ZnFe₂O₄, increases the surface area of precipitated oxide precursors by inhibiting sintering during thermal treatment and during activation in H₂/CO reactant mixtures, leading to higher FTS rates than on ZnO-free precursors. ZnFe₂O₄ species do not reduce to active FTS structures, but lead instead to the loss of active components; as a result, maximum FTS rates are achieved at intermediate Zn/Fe atomic ratios. Cu increases the rate of Fe₂O₃ reduction to Fe₃O₄ by providing H₂ dissociation sites. Potassium increases CO activation rates and increases the rate of carburization of Fe₃O₄. In this manner, Cu and K promote the nucleation of oxygen-deficient FeO _x species involved as intermediate inorganic structures in reduction and carburization of Fe₂O₃ and decrease the ultimate size of the Fe oxide and carbide structures formed during activation in synthesis gas. As a result, Cu and K increase FTS rates on catalysts formed from Fe–Zn oxide precursors. Cu increases CH₄ and the paraffin content in FTS products, but the additional presence of K inhibits these effects. Potassium titrates residual acid and hydrogenation sites and increases the olefin content and molecular weight of FTS products. K increases the rate of secondary water–gas shift reactions, while Cu increases the relative rate of oxygen removal as CO₂ instead of water after CO is dissociated in FTS elementary steps. Through these two different mechanisms, K and Cu both increase CO₂ selectivities during FTS reactions on catalysts based on Fe–Zn oxide precursors.     

Strain rate and curing condition effects on the stress–strain behaviour of epoxy adhesive materials

Adhesive materials evolve properties that change significantly with the preparation procedures and curing conditions. In this study the effects of curing conditions (curing time and temperature), and strain rate on the stress–strain behaviour of the commercially available Lapox epoxy adhesive materials have been evaluated experimentally. The rectangular test specimens have been prepared with different curing temperatures and times. After preparation, the specimens have been tested in small scale tensile testing machine to investigate the stress–strain behaviour at room temperature. It has been observed that as the curing time or curing temperature is increased, the ultimate tensile strength and the elastic modulus of the material also increase. A four parameter hyperbolic tangent model has been fitted to the experimental data and the model constants have been evaluated for different curing conditions and strain rates. Furthermore, for a fixed curing time and strain rate, empirical equations have been developed for modelling the dependence of curing temperature on the stress–strain curves. Finally, the developed equations have been implemented into the finite element analysis of a lap joint to investigate the stress and strain distributions of the adhesive layer for different curing conditions (curing time and temperature).     

Effect of a sweeping air stream and gas–phase aspect ratio of an isothermal Stefan diffusion column on the experimental estimation of binary gas diffusivities

The Stefan column consists of liquid A evaporating into an inert/stagnant gas B with a sweeping B stream at the top. It was designed to estimate binary gas diffusivities, D_AB’s, but “end effects” such as gas mixing at the top and interfacial curvature have been either ignored or uncorrelated to the operational settings. This study’s hypothesis is that gas mixing at the top and the gas–phase aspect ratio affect D_AB estimation in the acetone (A)-ambient air (B) system at 50?°C. The sweeping stream Reynolds number (Re) and the gas–phase aspect ratio (AR?=?initial gas phase height to column internal diameter) were the variables tested. Isothermal evaporation-diffusion experiments were conducted in which the temporal interfacial descent was tracked. The settings were 492 ≤ Re ≤ 5378 and AR between 5 and 15. A 1D transport model allowed determination of the experimental diffusivity, D_AB,exp, by nonlinear regression. For Re < 600, the D_AB,exp errors relative to D_AB,CE (predicted by the Chapman–Enskog kinetic theory for low-density gases) were small and unrelated to AR, while for Re > 600 the errors increased considerably with Re and were inversely proportional to AR. This study is the first to relate the column’s operational settings to the D_AB estimation errors. The column should be operated at low sweeping gas Re and large AR for accurate D_AB,exp’s. The low Re region deserves further study, while the present transport model may have to be replaced by computational fluid dynamics simulations to account for the multidimensional gas flow patterns.