Matrix isolation technique for the study of some factors affecting the partitioning of trace elements

The factors that affect the preferred positions of cations in ionic solid solutions were investigated utilizing vibrational spectroscopy. Solid solutions of the sulfate and chromate ions codoped with La(+3) and Ca(+2) in a KBr host lattice were examined as a function of the polyvalent cation concentration. The cation-anion pairing process was found to be random for Ca(+2), whereas the formation of La(+3)-SO4(-2) ion pairs with a C2 sub v bonding geometry is highly preferential to any type of La(+3)-CrO4(-2) ion pair formation. The relative populations of ion pair site configurations are discussed in terms of an energy-entropy competition model which can be applied to the partition of trace elements during magmatic processes

Direct vs. indirect optical recombination in Ge films grown on Si substrates

The optical emission spectra from Ge films on Si are markedly different from their bulk Ge counterparts. Whereas bulk Ge emission is dominated by the material's indirect gap, the photoluminescence signal from Ge films is mainly associated with its direct band gap. Using a new class of Ge-on-Si films grown by a recently introduced CVD approach, we study the direct and indirect photoluminescence from intrinsic and doped samples and we conclude that the origin of the discrepancy is the lack of self-absorption in thin Ge films combined with a deviation from quasi-equilibrium conditions in the conduction band. The latter is confirmed by a simple model suggesting that the deviation from quasi-equilibrium is caused by the much shorter recombination lifetime in the films relative to bulk Ge

Identification of flow boiling patterns in mini channel with the use of analysis of pressure oscillations

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.The dynamics of pressure fluctuations occurring in flow boiling in a minichannel with diameter of 1 mm, which consists of the heated section and glass condenser has been experimentally investigated and analysed. The recurrence plot and PCA of recurrence plot quantities have been applied. High speed digital video camera has been used to identify two-phase flow patterns in the glass condenser. The low frequency pressure fluctuations with relatively high amplitude which are caused by presence of compressible volume in the system have been observed. These fluctuations are accompanied by high frequency pressure oscillations. It has been found that during those fluctuations the dominant frequency of pressure fluctuations changes chaotically in time. Such pressure oscillations are accompanied by the flow patterns changes in the condenser. In the paper the new method of two-phase flow identification has been presented. The method is based on the analysis of dynamics of signal recorded from the pressure sensor. It has been shown that in the plots of two first components the points are grouped in the six separated clusters, which correspond to different flow patterns.dc201

Modelling long term pressure and temperature oscillations in the flow boiling in microchannels

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Heat exchangers equipped with microchannels have many industrial applications. This is due to their capability for transfer of high heat fluxes. In flow boiling in microchannels three different flow regimes: steady bubbly/slug flow regime, bubbly/annular alternating flow and annular/mist alternating flow have been observed. In the present paper the model of heat and mass transfer in microchannels system has been proposed. Oscillations between quasi steady state of boiling in microchannels have been considered. Changes of two-phase flow in microchannels have been described by the relations between: heating surface temperature, vapour quality, liquid mass flux, pressure drop in microchannels and heat flux absorbed by boiling liquid. Simulation results indicate that shape of curve pressure-drop-versus-flow-rate is responsible for appearance or disappearance of heating surface temperature and pressure oscillations.dc201

Yukawa potentials in systems with partial periodic boundary conditions II : Lekner sums for quasi-two dimensional systems

Yukawa potentials may be long ranged when the Debye screening length is large. In computer simulations, such long ranged potentials have to be taken into account with convenient algorithms to avoid systematic bias in the sampling of the phase space. Recently, we have provided Ewald sums for quasi-two dimensional systems with Yukawa interaction potentials [M. Mazars, {\it J. Chem. Phys.}, {\bf 126}, 056101 (2007) and M. Mazars, {\it Mol. Phys.}, Paper I]. Sometimes, Lekner sums are used as an alternative to Ewald sums for Coulomb systems. In the present work, we derive the Lekner sums for quasi-two dimensional systems with Yukawa interaction potentials and we give some numerical tests for pratical implementations. The main result of this paper is to outline that Lekner sums cannot be considered as an alternative to Ewald sums for Yukawa potentials. As a conclusion to this work : Lekner sums should not be used for quasi-two dimensional systems with Yukawa interaction potentials.Comment: 25 pages, 5 figures and 1 tabl