Phase Behavior of Aqueous Na-K-Mg-Ca-CI-NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na{sup +}, K{sup +}, Mg{sup 2+}, Ca{sup 2+}, Cl{sup -}, and NO{sub 3}{sup -} ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 C. The measurements have been performed using Oak Ridge National Laboratory's (ORNL) previously designed gravimetric isopiestic apparatus, which makes it possible to detect solid phase precipitation. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid-liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor-liquid and solid-liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems

Nematic director response in ferronematic cells

This paper examines ferronematic switching in a homeotropic cell in the presence of a magnetic field normal to the cell plane. At low fields we find thresholdless switching of the nematic director, consistent with experimental data. At higher fields, there are three regimes, depending on the strength of the director-ferroparticle coupling. For low coupling, there is an inverse Frederiks effect: the nematic reorientation increases and then reduces, disappearing at a critical field. At intermediate coupling, the reorientation reduces at high fields but remains finite. For high coupling, however, the director switching saturates. There is a dimensionless temperature scale t involving the temperature, the mean nematic elastic constant, the colloidal density and the cell dimension. For low t, high magnetic fields can cause the ferroparticles to segregate. The segregation is coupled to the director distortion, and this can drive the inverse Frederiks transition first order, causing bistability for intermediate fields. These features are perturbed but not changed structurally by the effect of a small bias magnetic field ( <10Oe) normal to the unperturbed director

New evidences about human activities during the first part of the Upper Pleniglacial in Ukraine from zooarchaeological studies

The Upper Pleniglacial, between 23 000e20 000 BP, is characterized by the intensification of cold climate and is followed by the maximum extent of ice sheets. There is a little bit information about the human activities during this period. New archaeological excavations in Ukraine permit to evidence data about behavioural human adaptations. These open air sites are on the one hand Pushkari 1 (excavation VII), Pogon (excavation VII) and Obollonia in the Desna valley and on the other hand Dorochivtsy III in the Dniester valley. These sites are characterised by atypical lithic industries made on local flint relied to the Gravettian but containing Epigravettian or Aurignacoid elements. In order to better understand the subsistence strategy we carried out zooarchaeological and taphonomical studies, which allow us to reveal the strategy of fauna exploitation by the human groups. We highlighted that all these sites are characterized by a restricted faunal spectrum with the presence of mammoth, reindeer, horse and carnivores (mainly fox [Vulpes vulpes and Alopex lagopus] and wolf). In the Dniester valley the reindeer was the most exploited, whereas the mammoth is the most exploited in the Desna valley. Indeed, it was probably hunt in Pushkari 1, maybe in Pogon and Obollonia. It was exploited as combustible, food resources and bones as raw material. In Dorochivtsy III/6 ivory was used to make tools and as artistic support. Indeed this site and Obollonia present grooved ivory points, this is the oldest occurrence of this kind of artefacts in the both regions. Moreover two engraved tusks presenting more or less figurative pictures were found in Dorochivtsy III/l.6 and Obollonia. The other large herbivores were also consumed and carnivores were exploited for their pelts in all these sites. The settlements are recurrent camps with little development occupied during varied seasons oriented to hunting and butchering activities linked with exploitation of local flint. These sites demonstrate the continuity of human occupations within the Eastern European plain, with the persistence of hunting methods and the relative diversity of animal exploitation, during the Upper Pleniglacial. These sites are really important for the understanding of cultural processes in the Eastern European Upper Palaeolithic, and particularly for the understanding of Epigravettian origin