Adsorption of mono- and multivalent cat- and anions on DNA molecules

Adsorption of monovalent and multivalent cat- and anions on a deoxyribose nucleic acid (DNA) molecule from a salt solution is investigated by computer simulation. The ions are modelled as charged hard spheres, the DNA molecule as a point charge pattern following the double-helical phosphate strands. The geometrical shape of the DNA molecules is modelled on different levels ranging from a simple cylindrical shape to structured models which include the major and minor grooves between the phosphate strands. The densities of the ions adsorbed on the phosphate strands, in the major and in the minor grooves are calculated. First, we find that the adsorption pattern on the DNA surface depends strongly on its geometrical shape: counterions adsorb preferentially along the phosphate strands for a cylindrical model shape, but in the minor groove for a geometrically structured model. Second, we find that an addition of monovalent salt ions results in an increase of the charge density in the minor groove while the total charge density of ions adsorbed in the major groove stays unchanged. The adsorbed ion densities are highly structured along the minor groove while they are almost smeared along the major groove. Furthermore, for a fixed amount of added salt, the major groove cationic charge is independent on the counterion valency. For increasing salt concentration the major groove is neutralized while the total charge adsorbed in the minor groove is constant. DNA overcharging is detected for multivalent salt. Simulations for a larger ion radii, which mimic the effect of the ion hydration, indicate an increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure

Closing in on the properties of antihydrogen

Conference review, with some speculation in the closing section

ROOT AND SHOOT GROWTH OF DRACAENA FRAGRANS 'MASSANGEANA': CORRELATIONS WITH CANE CIRCUMFERENCE

Root and shoot development of Dracaena fragrans 'Massangeana' was determined 51, 72, 93, and 114 days after fresh cut cane was planted. Basal circumference of canes varied from 13.5 to 19.5cm. At each sampling date, root:shoot ratio was affected by cane circumference. As cane circumference increased above 14.5cm, root length and root:shoot ratio decreased. Number of developing shoots was not affected by cane circumference at any sampling date. Leaf area was not affected until sampling day 114, when it increased as circumference increased. ----- Se evaluaron los efectos de seis tratarnientos sobre el desarrollo radicular en canas de Oreceene fragrans "Massangeana", Los tratamientos fueron: (a) aniIIado a 12cm. de Ia base de la catta, (b) anillados a 6 y I2cm. de la base de la cai{a, (c) muescado usando un grupo de tres pequenos incisiones horizontales a I2cm. de la base de la cana, (d) muescado unsando dos grupos de tres pequenos incisiones horizontales a 6 y 12cm. de las base de la caii'a, (e) cortes longitudinales utilizando tres incisiones de 12cm. de largo distribuidas cada 120 ualrededor de la caiia y, (f) control. Aunque el desarrollo radicular fue afectado por los diferentes tratamientos, la circunferencia de las caffas tambien ejercid' una fuerte influencia. Las canas con las mayores y menores circunferencias desarrollaron un sistema radicular menos extenso que aquellas de tamaiio medio, mientras que el optimo desarrollo foliar ocurrio' en aquellas caiias de circunferencia mayor

Defining the clinical and cognitive phenotype of child savants with autism spectrum disorder

Objective: Whilst savant syndrome is most commonly observed in individuals with Autism Spectrum Disorder (ASD), it has historically been associated with intellectual impairment, and little is known about the clinical and cognitive characteristics of intellectually able individuals with ASD and savant skills. Methods: Participants with ASD and validated savant skills were compared with age and intelligence matched non-savants with ASD using a range of diagnostic and standardised tests. Results: Although the analysis of the clinical data revealed few differences between the groups, striking differences emerged during cognitive testing. Children with savant skills exhibited highly superior working memory and their scores on tests of analytic skills were also superior to those of non-savants. Conclusion: We propose that obsessionality, focused attention, superior working memory and analytic skills facilitate veridical mapping and pattern perception abilities characteristic in savant syndrome