12 research outputs found
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
Learners' perceptions of their successes and failures in foreign language learning
This is a postprint of an article whose final and definitive form has been published in the Language Learning Journal © 2004 Copyright Taylor & Francis; Language Learning Journal is available online at http://www.informaworld.comResearch into learnersâ attributions for their successes and failures has received considerable attention. However very little has been carried out in the area of learning foreign languages. This study is timely in view of the current interest by the government in promoting foreign languages.
The aims of the study were (1) to investigate secondary studentsâ attributions for their success and failures in learning foreign languages (2) to examine the ways in which these vary according to age, gender, perceived success and specific language studied.
The sample consisted of 285 students between the ages of 11 and 16 studying French, German and Spanish in five secondary schools in the UK. A simple open questionnaire was administered by language teachers, consisting of a personal evaluation by students of their perceived level of success as learners of specific foreign languages and their attributions for success and failure in those domains.
The resulting responses were analysed by means of a grounded theory approach allowing categories to emerge from the data. The resultant categories were then tabulated according to student age, gender, and language learnt, together with level of perceived success.
Over one thousand attributional statements gave rise to 21 attributional categories for doing well and 16 categories for not doing well at language learning. A far wider range of attributions were identified than is generally shown in the research literature, six of which were most commonly called upon as reasons for both success and failure. Clear differences emerged between boys and girls, year groups, perceived success and language studied. These results and, in particular, the lack of clarity in the learnersâ comments about strategy use and the lack of focus on metacognitive strategies, have important implications for policy makers and for teachers of foreign languages in UK schools. In addition there are important implications for future research in this area