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Phase Shows (phase + shows)
Selected AbstractsReversible addition,fragmentation chain-transfer graft polymerization of styrene: Solid phases for organic and peptide synthesisJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2002Leonie Barner Abstract The ,-initiated reversible addition,fragmentation chain-transfer (RAFT)-agent-mediated free-radical graft polymerization of styrene onto a polypropylene solid phase has been performed with cumyl phenyldithioacetate (CPDA). The initial CPDA concentrations range between 1 × 10,2 and 2 × 10,3 mol L,1 with dose rates of 0.18, 0.08, 0.07, 0.05, and 0.03 kGy h,1. The RAFT graft polymerization is compared with the conventional free-radical graft polymerization of styrene onto polypropylene. Both processes show two distinct regimes of grafting: (1) the grafting layer regime, in which the surface is not yet totally covered with polymer chains, and (2) a regime in which a second polymer layer is formed. Here, we hypothesize that the surface is totally covered with polymer chains and that new polymer chains are started by polystyrene radicals from already grafted chains. The grafting ratio of the RAFT-agent-mediated process is controlled via the initial CPDA concentration. The molecular weight of the polystyrene from the solution (PSfree) shows a linear behavior with conversion and has a low polydispersity index. Furthermore, the loading of the grafted solid phase shows a linear relationship with the molecular weight of PSfree for both regimes. Regime 2 has a higher loading capacity per molecular weight than regime 1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4180,4192, 2002 [source] Ion-pair mediated transport of small model peptides in liquid phase micro extraction under acidic conditionsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 3 2005J. Léon E. Reubsaet Abstract This paper discusses the behaviour of five small model peptides in a three phase (aqueous donor-organic-aqueous acceptor) liquid phase micro extraction system in relation to their physico-chemical properties (charge, hydrophobicity). It is proved that for all peptides transport over the organic phase is mediated by aliphatic sulphonic acids. Heptane-1-sulphonic acid gave the best overall recoveries. It appeared that peptides with hydrophobic properties (IPI) and a high number of positive charges (KYK) show good recoveries and are enriched in the acceptor phase. Variation in the pH (1.6,4.4) of the donor phase shows that there are peptide-dependent optimal pH-values for their recovery. Increasing pH in the acceptor phase shows that in most cases the recovery decreases due to decreased ion-pair mediated membrane transport. For KYK the partition between the organic phase and the aqueous acceptor-phase is also driven by the solubility in the aqueous acceptor phase. Increase of the ion strength of the acceptor phase did not affect the recovery of the peptides. Except for KYK, which showed decreased recovery when the ion strength increased. Another finding is that delocalisation of positive charge causes bad recovery, probably due to incomplete ion-pair-peptide complex formation. [source] X-ray powder diffraction and electron diffraction studies of the thortveitite-related L phase, (Zn,Mn)2V2O7ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009Kevin M. Knowles The phase designated ,-Zn3(VO4)2 reported as a minor second phase in zinc oxide-based varistor materials doped with vanadium oxide and manganese oxide is shown to be the L phase, (Zn1,,,xMnx)2V2O7 (0.188 < x < 0.538), in the pseudo-binary Mn2V2O7,Zn2V2O7 system. Analysis of X-ray powder diffraction patterns and electron diffraction patterns of this phase shows that the previously published a, c and , values for this thortveitite-related phase are incorrect. Instead, Rietveld refinement of the X-ray powder pattern of the L phase shows that it has a monoclinic C lattice with Z = 6, with a = 10.3791,(1), b = 8.5557,(1), c = 9.3539,(1),Å and , = 98.467,(1)°. Although prior convergent-beam electron diffraction work of `,-Zn3(VO4)2' confirmed the C Bravais lattice, the space group was found to be Cm rather than C2/m, the difference perhaps arising from the inability of the X-rays to detect small displacements of oxygen. Attempts to refine the structure in Cm did not produce improved R factors. The relationship between the crystal structure of the L phase and the high-temperature C2/m,,-Zn2V2O7 thortveitite-type solid solution is discussed. [source] X-ray diffraction study of the phase transition of K2Mn2(BeF4)3: a new type of low-temperature structure for langbeinitesACTA CRYSTALLOGRAPHICA SECTION B, Issue 3 2001A. Guelylah The potassium manganese tetrafluoroberyllate langbeinite compound has been studied in the temperature range 100,300,K. Using DSC measurements, a phase transition has been detected at 213,K. The space group of the low-temperature phase was determined to be P1121 using X-ray diffraction experiments and optical observations of the domain structure. The b axis is doubled with respect to the prototypic P213 cubic phase. Lattice parameters were determined by powder diffraction data [a = 10.0690,(8), b = 20.136,(2), c = 10.0329,(4),Å, , = 90.01,(1)°]. A precise analysis of the BeF4 tetrahedra in the low-temperature phase shows that two independent tetrahedra rotate in opposite directions along the doubled crystallographic axis. A symmetry mode analysis of the monoclinic distortion is also reported. This is the first report of the existence of such a phase transition in K2Mn2(BeF4)3 and also of a new type of low-temperature structure for langbeinite compounds. [source] Formation of spinel-cordierite-feldspar-glass coronas after garnet in metapelitic xenoliths: reaction modelling and geodynamic implicationsJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2007A. M. ÁLVAREZ-VALERO Abstract Spinel + cordierite + K-feldspar + plagioclase + glass form coronas around garnet in metapelitic xenoliths at El Hoyazo and Mazarrón, two localities of the Neogene Volcanic Province (NVP) of SE Spain. The presence of fresh glass (quenched melt) in all phases shows that corona development occurred under partial melting conditions. Algebraic analysis of mass balance in the NCKFMASH system suggests the reaction Grt + Sil + Bt + Pl = Spl + Crd + Kfs + melt as the most plausible model for the development of coronas in the El Hoyazo sample, and indicates that biotite was required as reactant for the formation of cordierite. The P,T conditions for the formation of coronas are estimated at ,820 ± 50 °C, 4.5 ± 0.6 kbar at El Hoyazo, and ,820 ± 50 °C, 4.0 ± 0.4 kbar at Mazarrón. The El Hoyazo xenoliths record a complex P,T history, characterized by early melt production during heating and additional melting during decompression. A local cooling event characterized by minor retrograde reaction and melt crystallization preceded ascent and eruption. This study shows that detailed xenolith analysis may be used to track magma evolution in a chamber. [source] Influence of the Quasi-Biennial Oscillation on the ECMWF model short-range-forecast errors in the tropical stratosphereTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 628 2007Nedjeljka, agar Abstract This paper addresses the impact of the Quasi-Biennial Oscillation (QBO) on the background-error covariances in the tropical atmosphere of the ECMWF model. The tropical short-range-forecast-error covariances are represented in terms of equatorial waves coupled to convection. By comparing the forecast-error proxy data from two different phases of the QBO, it is shown that the phase of the QBO has an effect on the distribution of tropical forecast-error variances between various equatorial waves. The influence of the QBO is limited to the stratospheric levels between 50 hPa and 5 hPa. In the easterly QBO phase, the percentage of error variance in Kelvin waves is significantly greater than in the westerly phase. In the westerly phase, westward-propagating inertio-gravity waves become more important, at the expense of Kelvin modes, eastward-propagating mixed Rossby-gravity waves and inertio-gravity modes. Comparison of datasets from two easterly phases shows that the maxima of stratospheric error variance in various equatorial modes follow the theory of the interaction of waves with descending shear zones of the horizontal wind. Single-observation experiments illustrate an impact of the phase of the QBO on stratospheric analysis increments, which is mostly seen in the balanced geopotential field. Idealized 3D-Var assimilation experiments suggest that background-error statistics from the easterly QBO period are on average more useful for the multivariate variational assimilation, as a consequence of a stronger mass-wind coupling due to increased impact of Kelvin waves in the easterly phase. By comparing the tropical forecast errors in two operational versions of the model a few years apart, it is shown here that recent model improvements, primarily in the model physics, have substantially reduced the errors in both wind and geopotential throughout the tropical atmosphere. In particular, increased wind-field errors associated with the intertropical convergence zone have been removed. Consequently, the ability of the applied background-error model to represent the error fields has improved. Copyright © 2007 Royal Meteorological Society [source] | |||||||||||||