Clumps and streams in the local dark matter distribution

In cold dark matter cosmological models, structures form and grow through the merging of smaller units. Numerical simulations have shown that such merging is incomplete; the inner cores of haloes survive and orbit as 'subhaloes' within their hosts. Here we report a simulation that resolves such substructure even in the very inner regions of the Galactic halo. We find hundreds of very concentrated dark matter clumps surviving near the solar circle, as well as numerous cold streams. The simulation also reveals the fractal nature of dark matter clustering: isolated haloes and subhaloes contain the same relative amount of substructure and both have cusped inner density profiles. The inner mass and phase-space densities of subhaloes match those of recently discovered faint, dark-matter-dominated dwarf satellite galaxies, and the overall amount of substructure can explain the anomalous flux ratios seen in strong gravitational lenses. Subhaloes boost gamma-ray production from dark matter annihilation by factors of 4 to 15 relative to smooth galactic models. Local cosmic ray production is also enhanced, typically by a factor of 1.4 but by a factor of more than 10 in one per cent of locations lying sufficiently close to a large subhalo. (These estimates assume that the gravitational effects of baryons on dark matter substructure are small.).     

Influence of local vascularity on hormone receptors in mammary gland

Procedures, such as teat removal (thelectomy) or teat duct ligation, which prevent removal of milk, lead to rapid involution of the lactating mammary gland; performed unilaterally they have been used previously to study the biochemistry of involution, enabling a comparison of normal and involuting glands in the same animal against the same systematic hormonal environment. Both the protein hormone prolactin and the steroid hormone oestrogen are of importance in the development and function of the mammary gland. In the present experiments, female Sprague-Dawley rats were unilaterally thelectomised and the binding to the mammary gland of prolactin and oestrogen was examined through pregnancy, lactation and weaning. There was an effect of thelectomy during lactation only, when levels of both receptors increased in the intact lactating gland but failed to rise in the thelectomised, involuting gland. Capillary closure is known to occur in the mammary glands of rats after 36-48 h of milk accumulation. The rate of delivery of hormones to the tissue will be drastically reduced and it is concluded that this, rather than systemic hormone levels, is of importance in controlling receptor levels.     

Tetramerization of an RNA oligonucleotide containing a GGGG sequence.

Poly rG can form four-stranded helices. The Hoogsteen-paired quartets of G residues on which such structures depend are so stable that they will form in 5'-GMP solutions, provided that Na+ or K+ are present (see for example, refs 2-4). Telomeric DNA sequences, which are G-rich, adopt four-stranded antiparallel G-quartet conformations in vitro, and parallel tetramerization of G-rich sequences may be involved in meiosis. Here we show that RNAs containing short runs of Gs can also tetramerize. A 19-base oligonucleotide derived from the 5S RNA of Escherichia coli (strand III), 5'GCCGAUGGUAGUGUGGGGU3', forms a K(+)-stabilized tetrameric aggregate that depends on the G residues at its 3' end. This complex is so stable that it would be surprising if similar structures do not occur in nature.     

Linkage of an X-chromosome cleft palate gene

Many congenital malformations, such as cleft palate and neural tube defects, have a multifactorial origin involving both environmental and genetic factors. Conditions such as these may be exclusively monogenic, polygenic or environmental, but in most cases both genetic and environmental factors are involved. This study describes the sub-chromosomal localization of a single gene defect causing cleft palate and ankyloglossia (tongue-tied) in a large Icelandic family. This defect is a model for the analysis of other neural-crest malformations that show a more complex multifactorial inheritance pattern.     

Biasing reaction pathways with mechanical force

During the course of chemical reactions, reactant molecules need to surmount an energy barrier to allow their transformation into products. The energy needed for this process is usually provided by heat, light, pressure or electrical potential, which act either by changing the distribution of the reactants on their ground-state potential energy surface or by moving them onto an excited-state potential energy surface and thereby facilitate movement over the energy barrier. A fundamentally different way of initiating or accelerating a reaction is the use of force to deform reacting molecules along a specific direction of the reaction coordinate. Mechanical force has indeed been shown to activate covalent bonds in polymers, but the usual result is chain scission. Here we show that mechanically sensitive chemical groups make it possible to harness the mechanical forces generated when exposing polymer solutions to ultrasound, and that this allows us to accelerate rearrangement reactions and bias reaction pathways to yield products not obtainable from purely thermal or light-induced reactions. We find that when placed within long polymer strands, the trans and cis isomers of a 1,2-disubstituted benzocyclobutene undergo an ultrasound-induced electrocyclic ring opening in a formally conrotatory and formally disrotatory process, respectively, that yield identical products. This contrasts with reaction initiation by light or heat alone, in which case the isomers follow mutually exclusive pathways to different products. Mechanical forces associated with ultrasound can thus clearly alter the shape of potential energy surfaces so that otherwise forbidden or slow processes proceed under mild conditions, with the directionally specific nature of mechanical forces providing a reaction control that is fundamentally different from that achieved by adjusting chemical or physical parameters. Because rearrangement in our system occurs before chain scission, the effect we describe might allow the development of materials that are activated by mechanical stress fields.