Search results for "Crystallization"
showing 10 items of 774 documents
New Results on the Collapse Transition(s) of Flexible Homopolymers
2007
We analyze the collapse transition of flexible homopolymer chains in the bond-fluctuation model employing the Wang-Landau Monte Carlo algorithm. The coil-globule transition is followed by a first order transition into a solid state occurring in the collapsed globule. In the thermodynamic limit (chain length to infinity) the topology of the phase diagram depends on the range of the attractive interaction between the monomers. For sufficiently large interaction range a normal behaviour of a continuous coil-globule transition at the Θ-temperature followed by a crystallization transition at lower temperature is observed. For short interaction range the first-order transition asymptotically can …
Non-isothermal crystallization kinetics of PET
2000
The crystallization kinetics of poly(ethylene terephthalate) was studied using constant cooling rate, isothermal and quenching experiments. A non-isothermal crystallization kinetics equation based on a single mechanism was used to analyze the data. Different mechanisms of crystallization at low, intermediate, and high cooling rates were hypothesized based on deviation of the experimental data from the single mechanism model.
The interplay of crystallization kinetics and morphology during the formation of SnO2 nanorods: snapshots of the crystallization from fast microwave …
2011
A microwave-assisted reaction pathway to rutile SnO2nanorods was investigated. The microwave-treatment significantly reduces the reaction time compared to standard hydro-/solvothermal techniques. By moving the overall process into a shorter time slot, the growth and crystal formation during the reaction could be monitored via snapshots by trapping the intermediates through quenching. To gain a better insight into the template-free growth of one-dimensional (1D) nanostructures, a parameter-dependent (various temperatures/pressures and times were investigated) study was carried out. For all materials, the phase purity and crystallite sizes were determined by X-ray powder diffraction (XRD). Th…
Structure development in poly(ethylene terephthalate) quenched from the melt at high cooling rates: X-ray scattering and microhardness study
2000
The structure and microhardness of poly(ethylene terephthalate) (PET) cooled from the melt, using a wide range of cooling rates, was studied. PET thin films rapidly cooled from the melt (cooling rates larger than 5°C/s) show a continuous variation of structure and properties depending on cooling rate. Results highlight differences in the micro-mechanical properties of the glass suggesting the occurrence of amorphous structures with different degrees of internal chain ordering. The comparative X-ray scattering study of two glassy PET samples (7500 and 17°C/s) reveals the occurrence of frozen-in electron density states giving rise to an excess of scattering for the amorphous sample solidified…
Modeling the interactions between light and crystallizing polymer during fast cooling
2004
In this work, an experimental set-up able to quench thin polymer films whilst recording the sample thermal history as well as the overall and depolarized light intensities of a laser beam emerging from the sample is described. The interactions between the light beam and the crystallizing material have been modeled accounting for absorption and scattering phenomena. The proposed model was found to be able to reproduce the ex- perimentally observed behavior of light intensities and it was validated by comparison with conventional DSC analysis. On the basis of this model, a method to obtain crystallinity evo- lution is proposed and applied to some fast cooling runs. The method was applied to q…
Unraveling the role of the secretor antigen in human rotavirus attachment to histo-blood group antigens
2019
25 Páginas, 7 figuras, 2 tablas
Vinorine synthase from Rauvolfia: the first example of crystallization and preliminary X-ray diffraction analysis of an enzyme of the BAHD superfamily
2004
Abstract Crystals of vinorine synthase (VS) from medicinal plant Rauvolfia serpentina expressed in Escherichia coli have been obtained by the hanging-drop technique at 305 K with ammonium sulfate and PEG 400 as precipitants. The enzyme is involved in the biosynthesis of the antiarrhythmic drug ajmaline and is a member of the BAHD superfamily of acyltransferases. So far, no three-dimensional structure of a member of this enzyme family is known. The crystals belong to the space group P 2 1 2 1 2 1 with cell dimensions of a =82.3 A, b =89.6 A and c =136.2 A. Under cryoconditions (120 K), a complete data set up to 2.8 A was collected at a synchrotron source.
Heterologous expression, purification, crystallization and preliminary X-ray analysis of raucaffricine glucosidase, a plant enzyme specifically invol…
2006
Raucaffricine glucosidase (RG) is an enzyme that is specifically involved in the biosynthesis of indole alkaloids from the plant Rauvolfia serpentina. After heterologous expression in Escherichia coli cells, crystals of RG were obtained by the hanging-drop vapour-diffusion technique at 293 K with 0.3 M ammonium sulfate, 0.1 M sodium acetate pH 4.6 buffer and 11% PEG 4000 as precipitant. Crystals belong to space group I222 and diffract to 2.30 A, with unit-cell parameters a = 102.8, b = 127.3, c = 215.8 A.
Crystallization and preliminary X-ray crystallographic analysis of strictosidine synthase from Rauvolfia: the first member of a novel enzyme family.
2004
Strictosidine synthase is a central enzyme involved in the biosynthesis of almost all plant monoterpenoid indole alkaloids. Strictosidine synthase from Rauvolfia serpentina was heterologously expressed in Escherichia coli. Crystals of the purified recombinant enzyme have been obtained by the hanging-drop technique at 303 K with potassium sodium tartrate tetrahydrate as precipitant. The crystals belong to the space group R3 with cell dimensions of a=b=150.3 A and c=122.4 A. Under cryoconditions (120 K), the crystals diffract to about 2.95 A.
Growth of zircon and titanite during metamorphism in the granitoid-gneiss terrane south of the Barberton greenstone belt, South Africa
2005
AbstractSHRIMP U-Pb zircon and titanite dating have been used to constrain the timing of mid- to lower- crustal metamorphism (∼650—700°C and 8—11 kbar) and syn-kinematic melting in the granitoid gneiss- dominated terrane south of the Barberton greenstone belt, South Africa. This study is concentrated on a clastic metasedimentary unit exposed in one of several greenstone remnants and a late-kinematic trondhjemite intrusive into spatially associated mixed gneisses. Locally, the clastic metasediments show extensive replacement of garnet and plagioclase by epidote and titanite. The titanites yield an upper intercept date of 3229±9 Ma, and provide a minimum age for the peak of metamorphism. Zirc…