Gabriel dimension and spectral torsion theories

In the study of Ring Theory, several concepts of dimension have appeared; among others we can find the Krull dimension, the Gabriel dimension and the Goldie dimension. These concepts have provided many interesting constructions. In a general context, these concepts are diffe nt, although there are some relations among them.     

Optimization of aramid powder reinforced PP/EPDM blends

The effect of twaron powder on the tensile behavior and abrasion resistance of polypropylene (PP) and an ethylene‐propylene diene terpolymer (EPDM) and their blends has been investigated by means of an experimental design. The stiffness and strength of the composites with EPDM as continuous phase hardly varies with the addition of twaron powder, however, at high percentages of PP (above 50%) in the matrix, these properties decrease as powder content increases. In all cases the elongation at fracture decreases in the presence of the powder. A maximum in the abrasion resistance is observed in the 14% twaron powder filled polypropylene composite. From the results and the graphs of the response surfaces a better affinity between the twaron powder and the EPDM can be suggested. It can be also deduced that as twaron content in the composite increases, the phase inversion in the polymer matrix takes place at lower PP percentages. A good correlation between mechanical characteristics and morphological observations has been observed.     

Particle image velocimetry in Rayleigh-Be´rnard convection: Photographs with a high number of exposures

We present here an application of particle image velocimetry (PIV) to the analysis of the Rayleigh-Be´nard convection patterns in small ☐es, in which a low power laser (5 mW He-Ne) has been used and photographs with a high number of exposures have been taken. Parameters which affect the quality of photographs are analyzed and related with the number of exposures.

The data reduction is made by fringe analysis (point-by-point technique) and by spatial filtering (whole-field technique). The fringe analysis is made with a1 − D integration method, which has been fully automated in the way described here.

The velocity field is numerically processed in order to obtain some additional information (like flow rates, vorticity, streamlines, …) which is relevant in fluid mechanics.

Finally, results obtained from an application of the whole process to the study of motion in the mid-plane of a Rayleigh-Be´nard cell are shown.     

NMR and X-ray study of cyclotetraveratrilene derivatives

A conformational study of cycloveratrilenes 3 and 4 by high resolution NMR at low temperature for 3 and room temperature for 4 along with X-ray crystallography is reported. From these experiments we found a dynamic process, where magnetic and topologic environment are exchanged by conformational variations through rotations. A conformational study of two cyclotetraveratrilenes by high resolution NMR at low and room temperature along with X-ray crystallography is reported. From these experiments we found a dynamic process, where magnetic and topologic environment are exchanged by conformational variations through rotations.     

Use of enantiomerically pure methylsulfinylmethylisoxazolines in the stereoselective synthesis of 1,5,6,7-tetrahydroxy-3-heptanone derivatives

Aldol-type reactions of enantiomerically pure 4,5-diphenyl-3-(methylsulfinyl)methylisoxazolines and 2,3-O-isopropylidene- -glyceraldehyde were examined in order to establish the stereochemical preferences. Catalytic hydrogenation of the resulting trihydroxyisoxazoline derivatives using a Raney-Ni/H₃BO₃ system provides an access to diastereomerically pure 1,5,6,7-tetrahydroxy-3-heptanones.     

Molecular dynamics simulation of acetamide solvation using interaction energy components: Application to structural and energy properties

Molecular dynamics simulation of an aqueous solution of acetamide was performed using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions, and TIP3P to describe the water–water interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the molecular parameters of the solute–water interaction potential. The results showed that the functions that use the EX-PL-DIS-ES interaction model lead to good values of the structural and energy properties (in particular, the hydration shell and the solvation energies) when they are compared with those from using AMBER-derived parameters, and with the available theoretical and experimental data.     

A DFT study of the polar Diels-Alder reaction between 4-aza-6-nitrobenzofuroxan and cyclopentadiene

The polar Diels-Alder reaction between 4-aza-6-nitrobenzofuroxan (ANBF) and cyclopentadiene has been studied using DFT procedures at the B3LYP/6-31G* level. Only one highly asynchronous transition state structure associated to the formation of the [4+2] adduct 13 is found. A further [3,3] sigmatropic shift on the [4+2] cycloadduct 13 allows its conversion into the thermodynamically more stable [2+4] cycloadduct 14. The analysis of the global and local electrophilicities of the reagents correctly explain the behaviour of ANBF as a strong electrophile in polar cycloadditions.     

Scaling Behavior of the Rheological Properties of Montmorillonite Suspensions: Correlation between Interparticle Interaction and Degree of Flocculation

In this work we investigate some aspects of the rheological behavior of sodium montmorillonite (NaMt) suspensions in the pH range 3 to 9, of NaCl concentrations between 10(-3) and 10(-1) M, and of solid concentrations between 5 and 11% w/v. Three kinds of experiments were performed: steady-state viscometry, oscillatory test, and creep recovery. The physical quantities of interest were the yield stress sigma(y) of the suspensions, the elastic rigidity modulus G', and the instantaneous elastic compliance. Furthermore, G' was obtained from oscillatory tests in three different experiments: determination of the viscoelastic linear region, oscillograms, and the gelation process. All quantities were found to scale with the concentration of solids, C, according to a power law of the form Y=k(y)C(n). The exponents n were found to change from approximately 3 to approximately 6 when the pH was increased from 3 to 9 (at constant ionic strength 10(-2) M), although values as high as 10 were estimated when the NaCl concentration was reduced to 1 mM. Such values of n correlate well with the characteristics of the edge-to-face (E-F), edge-to-edge (E-E), and face-to-face (F-F) interparticle interactions. The minimum values of n correspond to maximum E-F attractions, whereas the largest n are associated with strong F-F repulsions. Copyright 2001 Academic Press.