Segregation of particulate solids in a rotating drum

Abstract

A drum of 12 inch diameter and 3 inch width containing two kinds of spherical balls was rotated and the segregation of balls along the cross-section of the drum was investigated. Plastic, glass and steel balls of 6.0, 12.5 and 15.3 mm diameter were used.

In order to measure the segregation of balls quantitatively, a segregation parameter, S, was defined.

Under the conditions of identical density but different diameters, the smaller balls were found to segregate. In the case of different densities but same diameter, the heavier balls tended to concentrate inside the bed. When the heavier, larger size balls and the lighter, smaller size balls were mixed, better mixing was observed. S was also found to change with the volume fraction of the heavier balls.

Empirical equations which represent the relationship between S and the experimental conditions, such as diameter ratio, density ratio and volume fraction of the heavier balls were derived.

Résumé

Les auteurs utilisent un tambour rotatif de 12 po. de diamètre et de 3 po. de largeur contenant deux sortes de billes sphériques afin d’étudier leur ségrégation Ie long de la section transversale du tambour. Des billes de plastique, verre et aeier de 6, 12.5 et 15.3 mm de diamètre ont été utilisées.

Afin de mesurer la ségrégation quantitativement, les auteurs définissaient un parameètre S.

La densité étant identique, les plus petites billes ont une tendance à la ségrégation. Dans Ie cas de densité différente mais de diamètre identique, les billes plus pesantes tendent à se concentrer vers l’intérieur. Une meilleure homogénéité a été observée, quand les billes denses et larges sont mélangées aux billes légères et petites. Le paramètre S change avec la fraction volumique des billes plus denses.

Les équations empiriques qui représentent la relation entre S et les conditions expérimentales (le rapport des diamètres, le rapport des densités et la fraction volumique des billes plus denses) ont été établies.     

Magic echoes and NMR imaging of solids

Solid state NMR imaging techniques based on magic echoes are reviewed. The theoretical background of magic echoes in general and their spatial encoding in particular is treated. The magic-echo imaging pulse sequences presently in use are described and discussed. Particular emphasis is devoted to those techniques, which allow the incorporation of spectroscopic or parameter-selective information. The applicability of these methods for the investigation of materials is demonstrated and perspectives for materials science are outlined.     

Proton MAS NMR spectra at high magnetic fields and high spinning frequencies: spectral simulations using floquet theory

We examined the relationship quality of 55 (27 girls) 9-year-old children with their mothers, teachers, and friends as rated by teachers and by the children themselves. The goal of this longitudinal study was to examine stability and continuity in the quality of children's relationships between infancy and 9 years of age. At age 9, children's perception of their relationships with their teachers was associated with their current teachers' ratings of their relationships with the children. Children's perceptions of their relationships with their mothers were consistent with earlier ratings of attachment security. Children's perceptions of their relationships with teachers were predicted by the quality of their attachment relationships with their first teachers. Children's perceptions of their friendship quality was predicted by preschool teacher ratings of friendship quality and the quality of their attachment relationships with their first teachers.     

Broadband dipolar recoupling in rotating solids: a numerical comparison of some pulse schemes

A numerical comparison of the dipolar recoupling performance of several previously published homonuclear recoupling schemes under magic angle-spinning conditions is presented. Emphasis is put on the recoupled polarization transfer in a two-spin system where the efficiency is studied as a function of resonance offsets in the presence and absence of chemical-shielding anisotropies. In addition, the effect of the rf field strength is investigated. Powder pattern line shapes are shown in the on-resonance case that reveal the distribution of dipolar couplings for each recoupling scheme. These results are compared to data computed with a purposely misset rf field strength to estimate the pulse scheme sensitivity to rf-inhomogeneity and experimental missettings.     

Determination of peptide phi angles in solids by relayed anisotropy correlation NMR

A solid state NMR method is presented for determination of a backbone dihedral angle phi in peptides, being based on the previously reported method, relayed anisotropy correlation (RACO) NMR [Y. Ishii et al., Chem. Phys. Lett. 256 (1996) 133]. In the present method, the 15N-1H and the 13C-1H dipolar tensors in the 1H-15N-13C-1H system are two-dimensionally (2D) correlated via polarization transfer from 15N to 13C under magic angle spinning (MAS). This method was applied to N-acetyl[1,2-13C,15N]D,L-valine, and the H-C-N-H dihedral angle was determined to be 154.0 +/- 1.4 degrees or 206.0 +/- 1.4 degrees, the former agreeing with the X-ray value of 154 +/- 5 degrees.     

Cytotoxicity and NMR spectral assignments of ergolide and bigelovin

A 10-year-old left-handed girl with a developmental stutter and agenesis of the corpus callosum with associated hydrocephalus ceased stuttering immediately upon initiation of steroid therapy for colitis. Steroid taper resulted in a recurrence of the stutter and resumption for treatment of recrudescent colitis caused its disappearance again. Baseline agenesis of the corpus callosum with hydrocephalus and the patient's course in the face of the known effects of steroids on white matter lend support to the hypothesis that stuttering reflects anomalous dominance and/or atypical interhemispheric connectivity, as evidenced by the fact that presumed alterations of white matter tracts affected speech rhythms/stuttering.     

The ultimate strength of solids

Abstract

There is an upper limit to the mechanical strength of any material under any particular test conditions. This limit is known as the ideal strength. The present paper attempts to define the ideal strength as closely as is presently possible. To this end, a brief account is first given of some of the highest strengths recorded experimentally. Then follows a short account of the published theoretical calculations of the ideal strength. Finally, the theoretical and experimental values are compared, and it is shown that in several instances these differ by less than a factor 2x.

Résumé

Il existe une limite supérieure de la résistance mécanique de tout rnatériau pour des conditions d'essai données. On donne a cette limite le nom dé résistance idéale. Dans l'article, on tente de définir la résistance idéale de la maniére la plus précise qu'il soit possible de la faire avec les connaissances actuelles. A cette fin, on présente d'abord un sommaire de quelqu'unes des plus hautes résistances déterminées expérimentalement. Suit une courte présentation des calculs théoriques pub liés pour la resistance idéale. Entin, on compare les valeurs théoriques et expérimentales, et on démontre que dans plusieurs cas elles différent par un facteur infériéur à 2.     

Assessment of statistical and neural networks methods in NMR spectral classification and metabolite selection

Magnetic resonance spectroscopy opens a window into the biochemistry of living tissue. However, spectra acquired from different tissue types in vivo or in vitro and from body fluids contain a large number of peaks from a range of metabolites, whose relative intensities vary substantially and in complicated ways even between successive samples from the same category. The realization of the full clinical potential of NMR spectroscopy relies, in part, on our ability to interpret and quantify the role of individual metabolites in characterizing specific tissue and tissue conditions. This paper addresses the problem of tissue classification by analysing NMR spectra using statistical and neural network methods. It assesses the performance of classification models from a range of statistical methods and compares them with the performance of artificial neural network models. The paper also assesses the consistency of the models in selecting, directly from the spectra, the subsets of metabolites most relevant for differentiating between tissue types. The analysis techniques are examined using in vitro spectra from eight classes of normal tissue and tumours obtained from rats. We show that, for the given data set, the performance of linear and non-linear methods is comparable, possibly due to the small sample size per class. We also show that using a subset of metabolites selected by linear discriminant analysis for further analysis by neural networks improves the classification accuracy, and reduces the number of metabolites necessary for correct classification.     

The solution conformations of amino acids from molecular dynamics simulations of Gly-X-Gly peptides: comparison with NMR parameters

The conformations that amino acids can adopt in the random coil state are of fundamental interest in the context of protein folding research and studies of protein-peptide interactions. To date, no detailed quantitative data from experimental studies have been reported; only nuclear magnetic resonance parameters such as chemical shifts and J coupling constants have been reported. These experimental nuclear magnetic resonance data represent averages over multiple conformations, and hence they do not provide unique structural information. I have performed relatively long (2.5 ns) molecular dynamics simulations of Gly-X-Gly tripeptides, surrounded by explicit water molecules, where X represents eight different amino acids with long side chains. From the trajectories one can calculate time averaged backbone chemical shifts and 3J(NH alpha) coupling constants and compare these with experimental data. These calculated quantities are quite close to the experimental values for most amino acids, suggesting that these simulations are a good model for the random coil state of the tripeptides. On the basis of my simulations I predict 3J(alphabeta) coupling constants and present dihedral distributions for the phi, psi, as well as chi1 and chi2 angles. Finally, I present correlation plots for these dihedral angles.