Shock strengths in clumps impacted by winds of increasing power

We have performed spherically symmetric and axisymetric hydrodynamic simulations of wind–clump interactions in order to determine the conditions under which a wind, impacting upon a clump and increasing in power with time, drives a strong shock into the clump. If the wind ram pressure and the clump thermal pressure are comparable when the impact first occurs, then the wind ram pressure must increase on a time-scale markedly smaller than the sound-crossing time of the clump if it is to drive a shock that becomes strong at any point in the clump. We comment on the possible relevance of this result for the dynamics and chemistry of hot cores in regions of high-mass star formation.     

A study of three extraction methods for hydrocarbons in marine sediment

Three methods for the extraction of hydrocarbons from surface sediments were studied. The methods were: (1) digestion by methanolic-KOH and extraction with methanol; (2) Soxhlet extraction with chloroform and (3) Soxhlet extraction with carbon tetrachloride. Results are presented and compared.     

On the contribution of grain surface reactions to interstellar molecule densities

Some recent arguments concerning the relevance of grain surface reactions to interstellar molecule formation are shown to be without foundation. It is probable that surface reactions, gas phase ion-molecule and neutral reactions all contribute to interstellar molecular densities.     

A second-order global solution of the ideal resonance problem

The Ideal Resonance Problem, as formulated in 1966 (Paper I), is defined by the Hamiltonian Following the procedure adopted in the construction of a first-orderglobal solution (Papers II, III, and V), we derive a second-order solution from the von Zeipel-Bohlin recursive algorithm of Paper II. The singularities inherent in the Bohlin expansion in powers of μ have been suppressed by means of theregularizing function of Paper III, and the singularities in the coefficients atAB″=0 have been removed by thenormalization technique of Paper V. As a check, it is shown that the global solution includes asymptotically theclassical solution, expanded in powers ofμ ², and carrying thecritical divisor B′.     

Drivers of afforestation in Northern Vietnam: Assessing local variations using geographically weighted regression

This article identifies drivers of forest transition in a province of Northern Vietnam between 1993 and 2000 by applying geographically weighted regression (GWR) analysis to remotely sensed and statistical data. The regression model highlighted the spatial variation of the relationship between the percentage of land afforested and its proximate causes. Factors identified as having a major impact on afforestation are: the presence or proximity of a wood-processing industry, the distance to highways, and land allocation to households. Whereas the two former variables are in most areas of the province positively correlated with afforestation, an unexpected negative correlation was observed for the latter. The analysis of these results, supported by an in-depth knowledge of the area and of the political context, leads to the conclusion that, during the time period considered, afforestation was largely driven by state organisations on protected state-owned land, and forestry was not a significant component of household economic activities.