Influence of the filler CaCO3 on the cure kinetic of the epoxy network diglycidyl ether of bisphenol a (BADGE n = 0) with isophorone diamine

The influence of the presence of CaCO₃ on the cure reaction of the epoxy network diglycidyl ether of bisphenol A with isophorone diamine has been studied. The total enthalpy of reaction, the glass transition temperature and the partial enthalpies at different isothermal temperatures have been determined using differential scanning calorimetry (DSC) in dynamic and isothermal mode. A kinetic model accounting the influence of the diffusion of the reactive groups at high conversions was used. All the kinetic parameters have been compared with those of the system without filler (CaCO₃). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Impact of human activity on NO soil fluxes

Changes in land use driven by the increasing demand of food are affecting the fluxes of trace gases to the atmosphere. The more important human activities that affect NO soil fluxes are: deforestation, intensification of agricultural practices, and biomass burning. In this review emphasis is given to identifying the physicochemical and biological processes involved in the changes, and no attempt to quantify their contribution to global or regional NO budgets is made.Conversion of tropical forest to pasture is occurring very rapidly. An increase of the NO emission is observed immediately after deforestation (1–5 years) followed by a significant decrease (below forest levels) in old pastures and secondary successional forests. It seems that deforested tropical areas produce, in the long term, less NO than primary forests. The observed changes are not completely understood, but are most likely driven by the availability of exchangeable nitrogen and the bacteria' population.Soil plowing and fertilization are important factors that affect NO fluxes in agricultural soils. Plowing increases soil porosity and aeration, as well increasing the surface area that is exposed to the atmosphere. These physical changes increase the production of soil nitrate, and the escape efficiency of NO from the soil, enhancing NO fluxes. The emission of NO from fertilized soils depends on many variables: type of fertilizer (i.e. ammonium, nitrate), the structure of the soil microbial community (e.g., populations of nitrifiers and denitrifiers), meteorogical conditions (e.g. soil moisture and temperature), and soil management (e.g. plowing). A combination of these factors should explain the large range reported for the fraction of N-fertilizer that is emitted as NO to the atmosphere. Measurements made in diverse ecosystems show that vegetation burning enhances NO soil emissions. However, it seems that different processes, which are not well understood, occur at the various sites; e.g., in the tropical savannah, enhanced emissions, from dry soils, are observed immediately after burning, whereas in Californian chaparral burned dry soils emit on average less than the unburned plots, and the fluxes only increase after soil wetting. Changes in the physical conditions of the soil surface and N availability are the most likely factors that explain the increased fluxes.     

A computer algebra approach to verification and deduction in many-valued knowledge systems

 A theoretical result [10] that relates tautological consequence in many-valued logics to the ideal membership problem in algebra is revisited. The intended use of the approach in this article and its implementation is the verification of consistency and the automated extraction of knowledge in rule-based knowledge systems. Programs are written in the CoCoA language. Four RBS are studied to illustrate the implementation.     

On the analysis of heterogeneous fluids with jumps in the viscosity using a discontinuous pressure field

Heterogeneous incompressible fluid flows with jumps in the viscous properties are solved with the particle finite element method using continuous and discontinuous pressure fields. We show the importance of using discontinuous pressure fields to avoid errors in the incompressibility condition near the interface.     

A finite point method for incompressible flow problems

A stabilized finite point method (FPM) for the meshless analysis of incompressible fluid flow problems is presented. The stabilization approach is based in the finite increment calculus (FIC) procedure developed by O?ate [14]. An enhanced fractional step procedure allowing the semi-implicit numerical solution of incompressible fluids using the FPM is described. Examples of application of the stabilized FPM to the solution of two incompressible flow problems are presented. Received: 30 June 1999 / Accepted: 21 September 1999     

The Fuzzy Project Scheduling Problem with Minimal Generalized Precedence Relations

In scheduling, estimations are affected by the imprecision of limited information on future events, and the reduction in the number and level of detail of activities. Overlapping of processes and activities requires the study of their continuity, along with analysis of the risks associated with imprecision. In this line, this article proposes a fuzzy heuristic model for the Project Scheduling Problem with flows and minimal feeding, time and work Generalized Precedence Relations with a realistic approach to overlapping, in which the continuity of processes and activities is allowed in a discretionary way. This fuzzy algorithm handles the balance of process flows, and computes the optimal fragmentation of tasks, avoiding the interruption of the critical path and reverse criticality. The goodness of this approach is tested on several problems found in the literature; furthermore, an example of a 15‐story building was used to compare the better performance of the algorithm implemented in Visual Basic for Applications (Excel) over that same example input in Primavera© P6 Professional V8.2.0, using five different scenarios.     

7-Amidocoumarins as Multitarget Agents against Neurodegenerative Diseases: Substitution Pattern Modulation

This study explores the potential of 7-amidocoumarins as multitarget agents against Parkinson's and Alzheimer's diseases, by modulating the substitution patterns within the scaffold. Sixteen compounds were synthesized via 7-amino-4-methylcoumarin acylation, and in vitro evaluation of the molecules against hMAO-A, hMAO-B, hAChE, hBuChE and hBACE1 was performed. Five compounds turned out to be potent and selective hMAO-B inhibitors in the nanomolar range, six displayed inhibitory activity of hMAO-A in the low micromolar range, one showed hAChE inhibitory activity and another one hBACE1 inhibitory activity. MAO-B reversibility profile of 7-(4’-chlorobenzamido)-4-methylcoumarin ( 10 ) was investigated, with this compound being a reversible inhibitor. Neurotoxicity on motor cortex neurons and neuroprotection against H₂O₂ were also studied, corroborating the safety profile of these molecules. Finally, theoretical ADME properties were also calculated, showing these molecules as good candidates for the optimization of a lead compound. Results suggest that by modulating the substitution pattern at position 7 of the scaffold, selective or multitarget molecules can be achieved.     

Ultracompact methane steam reforming reactor based on microwaves susceptible structured catalysts for distributed hydrogen production

Hydrogen is a potential green energy vector. Since the heating of the reforming processes commonly used for its production is obtained by burning hydrocarbons, it has a substantial CO₂ footprint. One of the most critical aspects in the methane steam reforming (MSR) reaction is the heat transfer to the catalytic volume, due to the high heat fluxes required to obtain high methane conversions. Consequently, the reactor has complex geometries, along with the heating medium being characterized by temperatures higher than 1000 °C; expensive construction materials and high reaction volumes are therefore needed, resulting in slow thermal transients. These aspects increase the costs (both operative and fixed) as well as cause a decrease in the whole process efficiency. The heat transfer limitations due to the endothermicity of methane steam reforming reaction could be effectively overcome by microwave (MW) heating. This heating technique, that depends only on the dielectric properties of the materials, can result in an efficient and faster method for transferring heat directly to the catalyst, thus generating the heat directly inside the catalytic volume. In this work, Ni-based catalysts, differing from each other by the Ni loading (7 and 15 wt% with respect to the washcoat) were prepared. The catalysts were characterized by means of several techniques and tested in the MW-assisted methane steam reforming reaction. Furthermore, the energy balance of the entire process was performed to calculate the energy efficiency, making a preliminary evaluation of its feasibility in distributed hydrogen production also possible. The results of the preliminary tests showed that the prepared structured catalysts are very susceptible to the MW radiation, and that in the presence of the MSR reaction, it is possible to make the system reach a temperature of 900 °C. In the same tests, the CH₄ conversion showed a good approach to the thermodynamic equilibrium values starting at temperatures of about 800 °C at a value of gas hourly space velocity (GHSV) of about 5000 h^?1. The energy efficiency of the lab-scale system, calculated as the ratio among the energy absorbed by the system and the energy supplied by the microwaves, was about 50%. Future studies will deal with the microwave reactor optimization, aiming at the increase of the energy efficiency of the system, as well as to obtain a higher CH₄ conversion at lower temperatures and increase the H₂ yield and selectivity.     

Spin-Crossover Grafted Monolayer of a Co(II) Terpyridine Derivative Functionalized with Carboxylic Acid Groups

The synthesis and characterization of a new Co(II) spin-crossover (SCO) complex based on 4′-(4-carboxyphenyl)−2,2′:6′,2″-terpyridine ligand are reported. This complex can be successfully grafted on silver surface maintaining the SCO behavior. Thus, atomic force microscopy (AFM), matrix assisted laser desorption ionization – time-of-flight mass spectrometry (MALDI-TOF MS), Raman spectroscopy, and XPS measurements, upon surface deposition, evidence the formation of a monolayer of intact molecules grafted through carboxylate groups to the Ag surface. Three different techniques: Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), supported by first-principles calculations, confirm that the deposited molecules undergo a gradual spin transition with temperature. This phenomenon is unprecedented for a monolayer of molecules directly grafted onto a metallic surface from solution.