Library

Notes: Investigation of preliminary evidence that Ga, Sc, and In influence the bulk and dynamic magnetic properties of hexagonal ferrites by means other than those supported in existing models has been undertaken. In SrFe12−xMxO19 (M=Ga, In) and BaFe12−xScxO19, the predominant 12k sublattice exhibits a remarkable splitting into two distinct subpatterns, 12k1 and 12k2: At x=0.3, hyperfine fields, Heff for 12k1 are 411, 408, and 405 kOe, respectively, and for 12k2 are 358, 339, and 311 kOe, respectively. The 12k1 hyperfine field values are virtually unchanged from that of the pure hexagonal ferrites and are independent of substitution level. Contrastingly, the abruptness of the drop in the 12k2 hyperfine field and its dependence on the nature of the substituting cation are remarkable. The relative intensity of the 12k2 component correlates with the concentration of nonmagnetic species on the 2b and 4f2 sites and with the magnetic anisotropy. Scandium seems to have a more profound influence on the magnetic structure and interactions than indium or gallium. Further, at technically significant substitution levels, Heff of the different sublattices exhibit broad and overlapping distributions of values far removed from their distinctiveness in the pure hexaferrites. Thus, the net magnetization of Ga, Sc, and In-doped hexaferrites results from a complex interplay of magnetic dilution on the 2b site, enhancement of the magnetization through substitutions on the 4f2 site, and a complex influence from the substitution-induced 12k2 sublattice. © 1999 American Institute of Physics.

Notes: An analysis is presented of the obstetric histories of 50 women with acute porphyria, comprising 39 with acute intermittent porphyria, 3 with variegate porphyria and 8 with hereditary coproporphyria. Fifty-four per cent of the women with acute intermittent porphyria had an acute attack of porphyria in pregnancy and/or the puerperium. Only one maternal death was recorded. One patient with variegate porphyria and two with hereditary coproporphyria had an attack related to pregnancy. The total fetal wastage was 13 per cent. The babies born to mothers with acute intermittent porphyria, who experienced an acute attack during pregnancy, were smaller than those in which no such attack occurred (P〈0·001). In 13 non-porphyric primigravidae there was a rise in urinary excretion of 8-aminolaevulinic acid, porphobilinogen and coproporphyrin up to the 28th week of gestation. It is probable that pregnancy has some deleterious effects in acute porphyria but the prognosis of the porphyric pregnancy is much better than the literature suggests.

Notes: Errors of oral reading which are self-corrected have a special significance in the understanding of the reading process. The common interpretation of the nature of self-corrections of oral reading errors is critically reviewed and empirical evidence is examined. Overt self-corrections by the child who is learning to read have often been interpreted as reflecting efficient reading. An alternative interpretation is that self-corrections to some extent reflect incomplete processing that occurs with premature responding. Some evidence is given consistent with the second interpretation. In several investigations of individual differences in the incidence of self-corrections it has been claimed that a high incidence is associated with high reading attainment. In these investigations relevant variables have been confounded, either by measuring incidence of self-corrections as a proportion of errors or by failure to match the text difficulty level for comparison groups of high and low progress readers. On the present evidence there is no adequate support for recommending that teachers attempt to increase the incidence of a child's self-corrections.〈section xml:id="abs1-2"〉〈title type="main"〉RÉSUMÉLes autocorrections et la lecture: évaluation des faitsCertains auteurs considgrént la classification et l'interprétation des fautes en lecture orale comme des moyens d'estimer l'apprentissage de la lecture. Bien que Yon puisse faire des réserves sur la pertinence de ces données dans leur ensemble pour rendre compte de la qualité de la compréhension de la lecture, l'analyse d'une certaine sort d'erreur parait bien convene à cet objectif. Il s'agit des fautes de lecture orale corrigées spontanément par le lecteur: les‘autocorrections'. Le but de cet article est d'évaluer les données empiriques concernant les autocorrections en lecture orale, et d'etablir leur rapport avec les autres aspects du processus de lecture. Les recherches effectuées par K.S. Goodman et M.M. Clay sont les plus connues sur ce sujet, mais il existe de nombreuses autres études fournissant également des informations sur l'autocorrection.Selon une interprétation commencement admise, chez les enfants qui apprennent a lire, une fréquence élevée des autocorrections refléte une lecture efficace. Selon une interprétation alternative, et incompatible avec la précedénte, les autocorrections reflétent, en partie, I'aspect inachevé du processus, souvent observé chez les enfants faisant des réponses prématurées.Une revue des résultats qui s'accordent avec la seconde interprétation conduit à conclure provisoirement que I'intérpretation la plus répondue des autocorrections ne peut etre acceptée sans quelques restrictions.Plusieurs recherches ont été effectuées sur les différences individuelles dans les autocorrections des enfants apprenant à lire. On a admis, dans un grand nombre de ces travaux, qu'une quantitéélevée d'autocorrections est associée à une aptitude élevée à lire. Mais on reléve des confusions fréquent quant aux variables pertinentes: l'index, fréquement employé, qui exprime la proportion entre la quantité d'autocorrections et I'ensemble des erreurs, n'a pas été suffisamment justifié, et pose probléme pour l'analyse des données fournies par la plupart des recherches. Ces considérations ne sont d'ailleurs pas limitations à l'analyse des autocorrections. Une sesigure mise en question vaut également pour d'autres catégories de réponses prélevées dans la lecture orale.Un second obstacle méthodologique réside dans les limites de la discriminabilité entre degré de difficulté des textes pour les lecteurs, et savoir-lire des lecteurs.Il existe des données qui paraissent en faveur de la notion que les lecteurs lents sont moins capables que les lecteurs rapides de corriger eux-mêmes, de façon sélective, des erreurs qui changent le sens d'un texte plutôt que des erreurs relativement acceptables. Cependant cette interpretation est entravée par l'une ou I'autre des deux sources possibles de confusion sur les variables.Cette discussion comporte une implication pratique: il n'existe pas actuellement de support empirique permettant d'affirmer que les lecteurs qui ont vite appris ont plus de discernement que les lecteurs moins avancés quant à la nature des erreurs qu'ils choisissent de corriger eux-mêmes. Les résultats actuellement publiés ne fournissent pas non plus d'arguments qui permettraient de recommander aux enseignants d'encourager les enfants a faire plus d'autocorrections en cours de lecture.

Notes: Dielectric current apertures are shown to be effective as intracavity lenses for reduced optical losses in vertical-cavity lasers. The Gaussian resonator theory is applied to obtain a mode radius, and this is shown to be in good agreement with experiment as well as a recently proposed uniform waveguide model. © 1996 American Institute of Physics.

Notes: Slug and bailer tests are being used increasingly to evaluate the hydraulic properties of “tight” geologic units. Although these pulse methods of stressing a system are used typically only on single wells, the repeated pulse method described here stresses the system in the same manner, but the response is measured in observation wells. This type of pulse test yields much the same information as conventional pumping tests, but it is easier to perform in very low permeability units.The observation well response hydrographs are analyzed by curve-matching techniques. In general, a unique set of type curves must be computed for each pulse test. These type curves are computed easily if the pulsed well is treated as a line-source (or sink). The accuracy of the value of transmissivity (T) determined from the line-source type curves compared to using the finite-diameter well solution depends both on the pulsed well radius (rc) and the time interval between pulses (Δt). If TΔt/rc2 is maintained greater than 50, then T determined from the line-source solution will be within 25% of that determined from more accurate, but computationally inconvenient, finite-diameter well type curves.The repeated-pulse test technique was applied to an experimental well array completed in the Conasauga Shale Formation at Oak Ridge National Laboratory. Values of transmissivity determined by the repeated-pulse method agreed well with the results of slug tests performed on each well individually, and in addition, provided information on storage coefficients and anisotropy at the site.

Notes: Communications