Search results for "quantitative"
showing 10 items of 2409 documents
La marginalidad electoral y política de la extrema derecha valenciana (2003-2015)
2017
El partido político España 2000 se auto define como “social patriota” y “anti inmigración” y en su discurso se aprecian elementos de formaciones neo populistas europeas que han obtenido importantes resultados electorales en la última década. Sin embargo, España 2000, tras más de diez años de historia, no ha conseguido el éxito de sus homólogos europeos. Por ello, el texto trata de ofrecer las claves que han favorecido su emergencia y moderado crecimiento en esta región española a través de una metodología cuantitativa y la técnica de inferencia ecológica y a partir de sus datos electorales. El resultado muestra el posible origen de su electorado y las características sociodemográficas de su…
Do pollinator distributions underlie the evolution of pollination ecotypes in the Cape shrub Erica plukenetii?
2013
Background and aims According to the Grant-Stebbins model of pollinator-driven divergence, plants that disperse beyond the range of their specialized pollinator may adapt to a new pollination system. Although this model provides a compelling explanation for pollination ecotype formation, few studies have directly tested its validity in nature. Here we investigate the distribution and pollination biology of several subspecies of the shrub Erica plukenetii from the Cape Floristic Region in South Africa. We analyse these data in a phylogenetic context and combine these results with information on pollinator ranges to test whether the evolution of pollination ecotypes is consistent with the Gra…
FIA-spectrophotometric determination of N-substituted phenothiazine derivatives by oxidation with a solid-phase reactor of manganese dioxide incorpor…
1995
Abstract The determination of several N -substituted phenothiazine derivatives was carried out by the reaction of the drug with managanese dioxide entrapped in a polymeric material in a packed-bed reactor; the oxidized drug was monitored at λ max . The calibration graph is linear over the range 5–50 μg/ml of phenothiazine derivatives with a relative standard deviation of 0.5–1% (at 10 μg/ml) and sample throughput of 40–48 h −1 . The influence of foreign compounds was studied and the method was applied to the determination of six different phenothiazine derivatives in pharmaceutical formulations.
FIA-AAS determination of salicylic acid by a solid-phase reactor of copper carbonate incorporated in polyester resin beads.
1994
Abstract The determination of salicylic acid was carried out by reaction of the drug with copper carbonate entrapped in a polymeric material in a solid-phase reactor; the released cupric ions were monitored by flame atomic absorption at 324.8 nm. The calibration graph is linear over the range 4.0–75 μg ml −1 of salicylic acid, with a relative standard deviation of less than 1.5% and a sample throughout of 257 h −1 . The influence of foreign compounds was studied and the method was applied to the determination of salicylic acid content in two different pharmaceutical formulations.
Excess free energy of nanoparticles in a polymer brush
2008
Abstract We present an efficient method for direct determination of the excess free energy Δ F of a nanoparticle inserted into a polymer brush. In contrast to Widom's insertion method, the present approach can be efficiently implemented by Monte Carlo or Molecular Dynamics methods also in a dense environment. In the present investigation the method is used to determine the free energy penalty Δ F ( R , D ) for placing a spherical particle with an arbitrary radius R at different positions D between the grafting plane and the brush surface. Deep inside the brush, or for dense brushes, one finds Δ F ∝ R 3 whereas for shallow nanoclusions Δ F ∝ R 2 , regardless of the particle interaction (…
1984
Colloidal crystallization dynamics
1997
At sufficiently strong interparticle interaction, colloidal particles may form ordered crystalline arrays much in analogy to atomic systems. Well characterized model colloidal suspensions have therefore become valuable model systems for the study of the kinetics of crystal nucleation, growth and ripening. Significant progress has been made in this area throughout the past few years. Precise control of interaction parameters and new instrumental developments have allowed for quantitative determination of nucleation rate densities and growth velocities in monodisperse ‘hard’ and ‘soft sphere’ systems. Results confirm classical theories of nucleation and growth adapted to colloidal systems. Th…
Structure of Polymer Brushes in Cylindrical Tubes: A Molecular Dynamics Simulation
2006
Molecular Dynamics simulations of a coarse-grained bead-spring model of flexible macromolecules tethered with one end to the surface of a cylindrical pore are presented. Chain length $N$ and grafting density $\sigma$ are varied over a wide range and the crossover from ``mushroom'' to ``brush'' behavior is studied for three pore diameters. The monomer density profile and the distribution of the free chain ends are computed and compared to the corresponding model of polymer brushes at flat substrates. It is found that there exists a regime of $N$ and $\sigma$ for large enough pore diameter where the brush height in the pore exceeds the brush height on the flat substrate, while for large enoug…
Single Molecules Probing the Freezing of Polymer Melts: A Molecular Dynamics Study for Various Molecule-Chain Linkages
2010
8 pages; International audience; We present molecular dynamics simulations of coarse-grained model systems of a glassforming polymer matrix containing fluorescent probe molecules. These probe molecules are either dispersed in the matrix or covalently attached to the center or the end of a dilute fraction of the polymer chains. We show that in all cases the translational and rotational relaxation of the probe molecules is a faithful sensor for the glass transition of the matrix as determined from a mode-coupling analysis or Vogel-Fulcher analysis of their R-relaxation behavior. Matrix and dumbbell related relaxation processes show a clear violation of the Stokes-Einstein-Debye laws. In accor…
Conformations, Transverse Fluctuations and Crossover Dynamics of a Semi-Flexible Chain in Two Dimensions
2014
We present a unified scaling description for the dynamics of monomers of a semiflexible chain under good solvent condition in the free draining limit. We consider both the cases where the contour length $L$ is comparable to the persistence length $\ell_p$ and the case $L\gg \ell_p$. Our theory captures the early time monomer dynamics of a stiff chain characterized by $t^{3/4}$ dependence for the mean square displacement(MSD) of the monomers, but predicts a first crossover to the Rouse regime of $t^{2\nu/{1+2\nu}}$ for $\tau_1 \sim \ell_p^3$, and a second crossover to the purely diffusive dynamics for the entire chain at $\tau_2 \sim L^{5/2}$. We confirm the predictions of this scaling descr…