The structure of schmidt's aluminium hydroxide gel

Résumé Les auteurs démontrent que le gel d'hydroxyde d'aluminium (gel deSchmidt) soumis aux rayons X diffractés et examiné au microscope électronique se révèle formé de particules différant par leur structure, leur morphologie et leur dimensions de celles du gel C-gamma deWillstätter, mais semblables à celles du gel C-béta du même nom.     

Asymmetrical responses to directional selection for radiation resistance and sensitivity inDrosophila

Zusammenfassung Es wurde eine Selektion auf Strahlenresistenz nach Bestrahlung vonDrosophila melanogaster mit⁶⁰Co--Strahlen während 5 Generationen mit gutem Erfolg erzielt, nicht aber eine solche auf erhöhte Strahlensensibilität. Der asymmetrische Selektionseffekt dürfte somit auf dominanter Vererbung der Resistenz beruhen. Familienselektion kann auch ohne Besthralung zu resistenten Stämmen führen.     

Variability within and between strains for mating behaviour parameters inDrosophila pseudoobscura

Résumé Chez un caryotype donné deDrosophila pseudoobscura on constate dans quelques lignées plus de variabilité dans la durée du comportement sexuel précédant l'accouplement que dans la durée de celui-ci.

---

---

Supported by the Commonwealth of Australia Scholarship and Fellowship Plan.     

A correlation between the ability to withstand high temperatures and radioresistance inDrosophila melanogaster

Résumé Dans une étude sur 18 races deD. melanogaster une corrélation a été trouvée entre les facultés de résistance aux températures élevées et à l'irradiation du Co⁶⁰.     

The exploitation of genetic heterogeneity among the founders of laboratory populations ofDrosophila prior to directional selection

Résumé Chacune de 16 souches, filiations de femelles uniques, et fécondées dans la nature, montrait une proportion caractéristique de mouches ayant plus de 4 soies scutellaires (soies supplémentaires). La sélection pour soies supplémentaires allait à une vitesse bien plus grande chez les lignées portant un haut niveau de soies supplémentaires que chez les lignées où ce niveau était plus bas. Ces résultats ont une répercussion importante sur la théorie des expériences de sélection.

---

---

This research was supported by the Australian Research Grants Committee. One of us (S.M.W.H.) was supported by a Commonwealth of Australia Postgraduate Award.     

Making an estimate of the number of people and households for Output Areas in the 2001 Census

This article describes an investigation into the best way to estimate robust totals for people and households at Output Area level. We show that computing the average of people and household counts across the set of tables in which the same count appears is a good strategy. When we compare the mean or median person and household counts with those produced by summing from the postcode directory, the two sets of numbers are usually very close. Using averages in this way for other population bases in the sets of tables is therefore recommended. This technique can also be applied to larger areas.     

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.     

A giant gamma-ray flare from the magnetar SGR 1806-20

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.