An age difference of two billion years between a metal-rich and a metal-poor globular cluster.

Globular clusters trace the formation history of the spheroidal components of our Galaxy and other galaxies, which represent the bulk of star formation over the history of the Universe. The clusters exhibit a range of metallicities (abundances of elements heavier than helium), with metal-poor clusters dominating the stellar halo of the Galaxy, and higher-metallicity clusters found within the inner Galaxy, associated with the stellar bulge, or the thick disk. Age differences between these clusters can indicate the sequence in which the components of the Galaxy formed, and in particular which clusters were formed outside the Galaxy and were later engulfed along with their original host galaxies, and which were formed within it. Here we report an absolute age of 9.9 ± 0.7 billion years (at 95 per cent confidence) for the metal-rich globular cluster 47 Tucanae, determined by modelling the properties of the cluster's white-dwarf cooling sequence. This is about two billion years younger than has been inferred for the metal-poor cluster NGC 6397 from the same models, and provides quantitative evidence that metal-rich clusters like 47 Tucanae formed later than metal-poor halo clusters like NGC 6397.

A tidally distorted dwarf galaxy near NGC 4449.

NGC 4449 is a nearby Magellanic irregular starburst galaxy with a B-band absolute magnitude of -18 and a prominent, massive, intermediate-age nucleus at a distance from Earth of 3.8 megaparsecs (ref. 3). It is wreathed in an extraordinary neutral hydrogen (H I) complex, which includes rings, shells and a counter-rotating core, spanning ∼90 kiloparsecs (kpc; refs 1, 4). NGC 4449 is relatively isolated, although an interaction with its nearest known companion--the galaxy DDO 125, some 40 kpc to the south--has been proposed as being responsible for the complexity of its H I structure. Here we report the presence of a dwarf galaxy companion to NGC 4449, namely NGC 4449B. This companion has a V-band absolute magnitude of -13.4 and a half-light radius of 2.7 kpc, with a full extent of around 8 kpc. It is in a transient stage of tidal disruption, similar to that of the Sagittarius dwarf near the Milky Way. NGC 4449B exhibits a striking S-shaped morphology that has been predicted for disrupting galaxies but has hitherto been seen only in a dissolving globular cluster. We also detect an additional arc or disk ripple embedded in a two-component stellar halo, including a component extending twice as far as previously known, to about 20 kpc from the galaxy's centre.

Tissue engineering and autologous transplant formation: practical approaches with resorbable biomaterials and new cell culture techniques.

The engineering of living tissues in vivo requires new concepts in cell culture technology. In contrast to conventional cell cultures, the development of tissues depends on a three-dimensional arrangement of cells and the formation or synthesis of an appropriate extracellular matrix. Special emphasis is given to the major role of the extracellular matrix and cell differentiation in an artificial tissue. New technical approaches of in vitro tissue engineering are compared to the natural development of tissues in vivo. Current methods using resorbable biomaterials, tissue encapsulation and perfusion culture are discussed. Major consideration is given to scaffold structures of biomaterials that define a three-dimensional shape of a tissue or guide matrix formation. The different goals of tissue engineering such as in vitro models and transplant production are taken into account in the described techniques. Practical concepts comprising cell multiplication and differentiation in subsequent steps for future clinical applications are outlined.

Resorbable polyesters in cartilage engineering: affinity and biocompatibility of polymer fiber structures to chondrocytes.

The resorbable polymers polyglycolic acid (PGA) and polylactic acid (PLA) are gaining increasing importance in tissue engineering and cell transplantation. The present investigation was focused on the biocompatibility and cell retaining behavior of PGA/poly-L-lactide (PLLA) (90/10) and PLLA nonwoven structures for the in vitro development of chondrocyte-polymer constructs. The effect of the relevant monomers to chondrocytes was analyzed. Type II collagen and poly-L-lysine were compared to improve loading of PGA/PLLA and PLLA polymer nonwovens with chondrocytes. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetra-zoliumbrom ide (MTT) test was applied for quantification. At concentrations above 2 mg/mL, glycolic acid was more cytotoxic than lactic acid. As shown by pH equilibration, the cytotoxic effect is not due merely to the acidity of the alpha-hydroxy acids. Regarding the degradation products, glycolic acid, and L(+) lactic acid, nonwovens of PLLA are more biocompatible with chondrocytes than nonwovens of polyglycolide. Collagen type II and poly-L-lysine generally improved cell seeding on resorbable polymers in tissue engineering; however, their efficiency varies depending on the type of fiber structure.

An evaluation of a secondary school primary prevention program on violence in intimate relationships.

A large-scale primary prevention program for wife assault and dating violence was evaluated, employing a measure of attitudes, by means of the London Family Court Clinic Questionnaire on Violence in Relationships. The target audience comprised all students in four high schools. A brief intervention, including a large group presentation on wife assault and dating violence, followed by classroom discussion facilitated by community professionals was instituted. Attitudes, knowledge and behavioral intentions were assessed prior to intervention, immediately afterward, and at five to six weeks postintervention, in a stratified classroom level random sample of the participants. Significant positive attitude, knowledge, and behavioral intention changes were found at posttest, and the majority of these were maintained at delayed follow-up. Striking sex differences were found, with females consistently showing better attitudes than males. A 'backlash' effect was noted among a small number of males after the intervention. It was hypothesized that this group may already be involved in abusive behavior and require secondary, rather than primary, prevention. Students reported a high level of awareness of and experience with violence in their own and their friends' dating and family relationships, and overwhelmingly endorsed primary prevention of relationship violence in the schools.