Chemical evolution in collapsing cores

We study the chemical evolution in the central core of contracting interstellar clouds. The chemical rate equations and the hydrodynamic equations are integrated simultaneously. The. contraction is followed from very low density (n = 10 cm(-3)) to a high-density core with n > 10(7) cm(-3). The chemical evolution is studied for various physical and chemical conditions, including the effects of varying the cosmic ray ionization rate, in order to understand the observed structures in TMC-1 and the extended ridge cloud in Orion. Our results give good agreement with the observations for models with fast ion-dipole reaction rates, low cosmic ray ionization rates and low depletion of N and S. It is also found that there should be different stages of evolution with different densities in these sources.

Chemistry in anisotropic asymptotic giant branch winds

We have constructed a model for chemistry in the outflow of an asymptotic giant branch (AGB) star, using a spheroidal anisotropy in density, after that used by Jura. The predicted distributions of a selection of representative species are shown, and it is suggested that the abundance distributions observed by interferometry in IRC + 10216 may be the result of directional variation in outflow velocity.

THE EFFECT OF RAPID NEUTRAL-NEUTRAL REACTIONS ON CHEMICAL-MODELS OF DENSE INTERSTELLAR CLOUDS

Recent experiments on rapid neutral-neutral reactions involving the radical CN at low temperature and the neutral C atom at room temperature suggest that atom-neutral and radical-neutral reactions may be generally more rapid at low temperature than hitherto thought. We have included a variety of rapid neutral-neutral reactions in our gas-phase chemical models of quiescent, dense interstellar clouds. We find the calculated abundances of many molecules to be greatly changed from previous values. In particular, the peak 'early-time' abundances of organic molecules are reduced.

OBSERVATIONS OF DEUTERATED CYANOACETYLENE IN DARK CLOUDS

We have observed DC3N and HC3N in a number of cold dust clouds in order to derive the degree of deuterium fractionation. We find that the ratio of DC3N to HC3N is large, at about 0.05 or more, and discuss the implications of this result for the synthesis of cyanoacetylene. The observations are most readily interpreted if the deuteration of HC3N is linked to that of cyclic C3H2, which is also observed to exhibit a large degree of deuterium fractionation. HC3N deuteration levels comparable with those we observed are found to he just compatible with the mechanism suggested by Howe & Millar, but with adjusted rate coefficients. Freeze-out on to grain surfaces is also considered, but produces widespread deuterium enhancement in many species. contrary to observed levels.

ALTERNATIVE ROUTES TO DEUTERATION IN DARK CLOUDS

We investigate new approaches to the deuteration of C3H2, HC3N and HC5N in dark clouds, following the suggestion that protonated HC3N might form different isomers, a linear structure (HC3NH+) being the most stable. We consider the effect of linear HC3NH+ and HC5NH+ on the formation of HC3N and HC5N, and find that deuteration ratios at approximately 10 K are reduced, in the case of HC3N to values significantly below those observed, such that a deuteration mechanism other than direct deuteron transfer is probably required for cold clouds.

CHEMISTRY IN A PROTOPLANETARY NEBULA

In this paper we investigate gas-phase chemistry in the remnant 'superwind' of a carbon-rich red giant star, during its transition to a planetary nebula. The interacting stellar winds model is used. It is found that during the first few hundred years of transition, significant abundances of a few small molecules and ions (e.g. CH+, CH2+, CH3+, CH, CH2, NH) may occur in the thin, dense, shocked shell of gas predicted by thiS model, but that most molecules observed in protoplanetary nebulae will be rapidly destroyed, through photodissociation by strong UV from the central star. If dense clumps are present during transition, they may allow the gas-phase formation and/or survival of small amounts of some molecules, such as HCN, CN, C2H2, and HC3N, until about 2000 yr after termination of the superwind; and young, fully developed planetary nebulae may show observable amounts of polyatomic molecules by this means. Such clumping may explain the existence of, e.g., HCN in NGC 7027.

Accounts of debates in the House of Commons, March– April 1731, supplementary to the diary of the first earl of Egmont

John Perceval (1685–1748), 1st Viscount Perceval and (from 1733) 1st Earl of Egmont, was an assiduous recorder of his own life and times. His diaries, published by the Historical Manuscripts Commission from manuscripts in the British Library, are the best source for parliamentary debates at Westminster in the 1730s. For the years 1730-1733, when Perceval sat in the Commons (as an Irish peer) they are remarkably full. His practice seems to have been to prepare two versions (presumably on the basis of notes taken in the House), the first attributing speeches to individuals, and the second, entered up in the diary, which listed speakers and summarized all arguments on each side. His letterbooks for 1731 contain accounts of five debates that embody his first editing process, with speeches attributed to individuals. They were sent to an Irish correspondent, Marmaduke Coghill, and largely omitted from the diary because Perceval had already transcribed them elsewhere. They are new to historians and cast light on two main issues: the unsuccessful attempts by Perceval and the ‘Irish lobby’ to persuade the British parliament to settle the Irish woollen trade, a question bedevilling Anglo-Irish relations in this period; and an attempt by the opposition to stir up anger against perceived Spanish aggression against Gibraltar. One of the most interesting features is the insight afforded into the Commons performances of Sir Robert Walpole: his management of debates, his own style of speaking, and his sharp exchanges with opponents like William Pulteney.

Social effects of collaborative learning in primary schools

There is conflicting evidence on whether collaborative group work leads to improved classroom relations, and if so how. A before and after design was used to measure the impact on work and play relations of a collaborative learning programme involving 575 students 9e12 years old in single- and mixed-age classes across urban and rural schools. Data were also collected on student interactions and teacher ratings of their group-work skills. Analysis of variance revealed significant gains for both types of relation. Multilevel modelling indicated that better work relations were the product of improving group skills, which offset tensions produced by transactive dialogue, and this effect fed through in turn to play relations. Although before intervention rural children were familiar with each other neither this nor age mix affected outcomes. The results suggest the social benefits of collaborative learning are a separate outcome of group work, rather than being either a pre-condition for, or a direct consequence of successful activity, but that initial training in group skills may serve to enhance these benefits.