The montane (shola) grasslands of Western Ghats, South India are a component of a landscape mosaic including the better-studied shola forests. The conservation of the grasslands depends upon understanding their ecology. This review compiles available information and aims to evaluate the conservation potential of these grasslands. Most studies on these grasslands are descriptive in nature. There is little information regarding habitat heterogeneity, landscape configuration, natural disturbance, grazing and productivity in maintaining the grasslands. Succession is poorly understood because of the short-term nature of most studies. Human activities have historically influenced these grasslands and will continue to do so in more intensive manner. Threats to these grasslands include habitat loss, fragmentation, fires, and invasive species.
The thermal elimination of NaCl from sodium chloroacetate, a polymerization reaction that takes place between 150 and 200‡C in the solid state, leads quantitatively to the simplest polyester, polyglycolide. Byin situ IR-spectroscopy, we have shown that the reaction proceeds smoothly and directly without intermediates or by-products. The endgroups of the polymeric product — ionised carboxylate groups (-COONa) and hydrogen-bonded alcohol groups (−COH) — are clearly detectable. It is therefore concluded that the polymer forms extended chains, not rings, during the course of this solid-state reaction. That corresponds well with the idea of a polymerization reaction in the solid state. However, this experiment does not exclude the formation of polyglycolide rings as further product because they do not contain any terminating groups.
The measurement of fission product cesium isotopes 135Cs and 137Cs at low femtogram (fg) 10−15 levels in ground water by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) is reported. To eliminate the natural barium
isobaric interference on the cesium isotopes, in-line chromatographic separation of the cesium from barium was performed followed
by high sensitivity ICP-MS analysis. A high efficiency desolvating nebulizer system was employed to maximize ICP-MS sensitivity
~10 cps/fg. The three sigma detection limit for 135Cs was 2 fg/mL (0.1 μBq/mL) and for 137Cs 0.9 fg/mL (0.0027 Bq/mL) measured from the standard with analysis time of less than 30 min/sample. Cesium detection and
135/137 isotope ratio measurement at very low femtogram levels using this method in a spiked ground water matrix is also demonstrated.
The inorganic sorbent potassium cobalt(II) hexacyanoferrate(II) was tested for removal of radiocesium from alkaline salt solutions that are typical of intermediate level radioactive wastes generated at spent fuel reprocessing plants in India. Excellent results were obtained both in batch equilibration and column operation.
The phase diagram of solid-solid equilibria in the system Ca3(PO4)-CaNaPO4 has been studied by thermal analysis. The results are confirmed by X-ray diffraction at different temperatures. This study was limited to that of mixtures in a temperature range determined by previous results. The present work confirms the existence of two metastable diagrams which are superimposed on the stable diagram.
Authors:G. Thomas, J. J. Gruffat, and M. Soustelle
The kinetics of heterogeneous reactions are in most cases studied by means of integral curves which represent the degree of reaction as a function of the time. Recently, rate vs. time curves have also been used for this purpose. The present paper draws attention to the importance of curves giving the degree of reaction as a function of the rate of reaction; these facilitate the investigation of separate points, make possible the interpretation of various factors, and provide valuable data concerning the mechanism. Three methods are suggested for preparing these curves and the decomposition of sodium hydrogen carbonate is given as an example.
Authors:M. Cohen, L. Porte, J-P Thomas, and J. Tousset
Une méthode d'étude de la composition stoéchiométrique de couches minces (10 à 500 μg/cm2) de verres chalcogénures est développée. L'étude des réactions nucléaire; induites par bombardement de protons de basse énergie
(<4 MeV) sur les éléments constitutifs Ge, As, Te et S, conduit à choisir la diffusion élastique et la détection de gammas
prompts pour le dosage simulatené. La précision et la sensibilité de la méthode sont discutées à partir des résultats obtenus.
L'utilisation de la résonance fine sur le soufre (p, p'γ) est appliquée à l'étude de l'homogénéité des cibles.
Authors:J. Giroux, M. Talvat, J. Thomas, and J. Tousset
Activation analysis by charged particles may encounter great difficulties when ‘parasitic’ reactions induce in the matrix
itself the same radionuclide as the one requested by the reaction for analytical aim. In this investigation we study reactions
inducing18F activity in silicon and we show the importance of these reactions for determining low levels of oxygen in silicon by the
. For irradiations carried out with 54 MeV α-particles, the profile of18F production in silicon presents an activity decreasing very rapidly from the surface to depths of 500 μm without any connection
activation curve. The diffusion of18F nuclides created at the surface from the oxide bed does not at all explain that result. The differences between these curves
are attributed to parasitic reactions inducing18F activity in silicon. In order to confirm the reaction
we also investigated the profile of24Na and29Al production by another parasitic reaction in silicon. It is pointed out that the choice of incident energy is quite primordial,
for analyses of oxygen in silicon with 54 MeV α-particles are not quite suitable. The best energy range appears to be around