Ice XII in its second regime of metastability

We present neutron powder diffraction results which give unambiguous evidence for the formation of the recently identified new crystalline ice phase[Lobban et al.,Nature, 391, 268, (1998)], labeled ice XII, at completely different conditions. Ice XII is produced here by compressing hexagonal ice I_h at T = 77, 100, 140 and 160 K up to 1.8 GPa. It can be maintained at ambient pressure in the temperature range 1.5 < T < 135 K. High resolution diffraction is carried out at T = 1.5 K and ambient pressure on ice XII and accurate structural properties are obtained from Rietveld refinement. At T = 140 and 160 K additionally ice III/IX is formed. The increasing amount of ice III/IX with increasing temperature gives an upper limit of T ~ 150 K for the successful formation of ice XII with the presented procedure.Comment: 3 Pages of RevTeX, 3 tables, 3 figures (submitted to Physical Review Letters

Neutron diffraction investigation and structural model for liquid gallium from room temperature up to 1 303 K

Neutron scattering measurements on liquid gallium have been carried out at 293, 838 and 1 303 K on the H10 spectrometer of the EL3 reactor at Saclay. The obtained structure factors and pair correlation functions are compared to various published data. A quasi-crystalline model related to the β monoclinic form of gallium is proposed in order to explain the shape of the structure factor of liquid gallium and its behaviour versus temperature.Des mesures de diffusion de neutrons par le gallium liquide ont été réalisées sur le spectromètre H10 du réacteur EL3 à Saclay. Les facteurs de structure et les fonctions de corrélation de paire obtenus sont comparés à divers résultats de la littérature. Un modèle quasi cristallin rattaché à la forme monoclinique β du gallium est proposé pour expliquer le comportement du facteur de structure du gallium à l'état liquide et son évolution en fonction de la température

X-RAY DIFFRACTION STUDY ON LIQUID AND NON CRYSTALLINE SOLID GALLIUM, BISMUTH AND MERCURY

An attempt is made to compare the structures deduced from X-ray measurements on some pure metals, both in the liquid and the non crystalline state. With Ga and Bi, the liquid and the amorphous solid structures show some similarities and seem to be correlated with the solid phase which occurs when crystallisation takes place. Different behaviour is found with Hg : the liquid structure factor differs from the structure factor in the amorphous state whose main peak is symmetric in form

Propriétés structurales du gallium liquide

On rappelle les principaux travaux concernant les propriétés structurales du gallium liquide obtenues par diffraction des rayonnements dans l'intervalle de température compris entre 163 K et 1 303 K. Le comportement en fonction de la température du facteur de structure présente certains désaccords avec les prévisions de la théorie de Schneider sur la limite de stabilité des liquides en surfusion. L'interprétation des données structurales montre qu'il y a une similitude entre l'ordre à courte distance dans le liquide et celui de la forme cristalline métastable β. Cette analogie et l'étude du potentiel interatomique conduisent à infirmer l'existence de liaisons courtes covalentes dans le liquide

A greenhouse investigation of responses to different water stress regimes of Laurus nobilis trees from two climatic regions

Plants from two populations of Laurus nobilis (Tunisia issued from a semi-arid inland site and Algeria originating from a coastal sub-humid area) were exposed during three months under similar controlled conditions to two stress intensities of permanent stress (60% (S1) and 20% (S2) of Held capacity) or to cyclic water stress, plants being re-watered when the soil moisture dropped to 60% (S11) or 20% (S22) of field capacity. One-year old plants displayed contrasting physiological strategies to cope with water stress. Algeria exhibited a higher decrease in osmotic potential (psi s) in relation to stress-induced proline accumulation. Glycinebetaine accumulated in response to drought in response to permanent stress (Algeria) or cyclic stress (Tunisia). The two populations had similar net photosynthesis (A) but Algeria exhibited higher water use efficiency (WUE) than Tunisia. A drought-induced increase in the apoplastic water content (AWC) was noticed in response to mild stress intensities (S1 and S11) in Tunisia and in response to higher stress intensities (S2 and S22) in Algeria in relation to a stress-induced accumulation of pectin and proportion of arabinose within the pectic fraction. Bulk modulus of elasticity (E) increased in Tunisia in response to permanent drought and in Algeria in response to cyclic stress, as a result of a stress-induced increase in cellulose (Algeria) or hemicellulose (Tunisia). It is concluded that water stress tolerance could be achieved by both osmotic and elastic adjustment in the coastal population which did not exhibit a prodigal water use comparatively to the inland population. Differences between populations are strongly influenced by the kinetics of water stress application. (C) 2009 Published by Elsevier Ltd