Search results for "Fractal"
showing 10 items of 329 documents
Computational Study of Nanosized Drug Delivery from Cyclodextrins, Crown Ethers and Hyaluronan in Pharmaceutical Formulations
2015
Abstract The problem in this work is the computational characterization of cyclodextrins, crown ethers and hyaluronan (HA) as hosts of inclusion complexes for nanosized drug delivery vehicles in pharmaceutical formulations. The difficulty is addressed through a computational study of some thermodynamic, geometric and topological properties of the hosts. The calculated properties of oligosaccharides of D-glucopyranoses allow these to act as co-solvents of polyanions in water. In crown ethers, the central channel is computed. Mucoadhesive polymer HA in formulations releases drugs in mucosas. Geometric, topological and fractal analyses are carried out with code TOPO. Reference calculations are…
The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC.
2007
The size-exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three-column sets studied are specifically formed by: (i) 'pure' micro-styragel, (ii) 'mixed' TSK Gel H(HR + XL + HR) and (iii) mixed TSK Gel H(XL + HR + XL). The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve i…
Fractal calibration in size-exclusion chromatography
2003
Abstract The elution behaviour of different polymer–solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or “ideal” SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fra…
Aggregation Processes and Formation of Silico-calco-alkaline Gels under High Ionic Strength
2002
This paper presents a systematic in situ study of the process of formation of silico-calco-alkaline gels starting from a liquid colloidal solution containing different alkaline ions and different calcium concentration until the final gel state. The combined use of X-ray and neutron small-angle scattering (SAS) and dynamical rheometry techniques lead to a consistent description of the structure of the aggregates and of the mechanisms of aggregation involved in gel formation. SAS results indicate that the aggregates are fractal objects, their structure strongly depending on calcium ion concentration. The differences in gelation kinetics for systems containing different alkaline ions were attr…
Multiple interactions between molecular and supramolecular ordering
1999
We report studies of the interplay among processes of molecular conformational changes, spinodal demixing of the solution, and molecular crosslinking involved in the physical gelation of a biopolysaccharide-water system. Multiple interactions and kinetic competition among these processes were studied under largely different absolute and relative values of their individual rates by appropriate choices of the quenching temperature at constant polymer concentration. Quenching temperature strongly affects the rate of growth but not the final value of the fractal dimension of the gel. Kinetic competition plays a central role in determining the final conformation of individual molecules and the s…
A Headful of T4 Coliphage DNA Packaged to Fasces-Like Globules in Fractal Models
1998
We present a new model for T4 DNA packaging based on fractal considerations. The proposed model is based on electron microscopic observations of spread and packaged DNA. The model takes into account enzymatically and unidirectionally driven packaging, and quick release of the DNA during infection. We also consider the different biochemical reactions of the packaging process.
Accessibilité aux commerces, service et aménités vertes et de loisirs dans un modèle fractal d'urbanisation : le cas du Luxembourg
2012
International audience; L'objectif de cette communication est de présenter quelques éléments de réflexion concernant l'accessibilité aux commerces et services dans un modèle de croissance résidentielle. Ces travaux sont menés dans le but de fournir des entrées à la simulation de scénarios d'extensions urbaines. Le terrain d'application de ce travail est le Grand-Duché de Luxembourg, où le développement pavillonnaire périurbain s'accompagne d'une forte dépendance automobile (Dupuy, 1995 ; pour le cas luxembourgeois cf. Petit, 2009). Pour endiguer ce processus, le Ministère des Transports ambitionne une part modale de 25% en transports en commun à l'horizon 2020 (Plan Sectoriel des Transports…
Villes, densité et fractalité
1995
International audience; Ce bref article résumé les résultats d'analyses fractales effectuées sur les villes françaises à plusieurs dates pour deux niveaux d'observation: les tissus urbains caractérisés par la distribution spatiale des surfaces bâties d'une part, et le semis des villes de différentes tailles dans l'ensemble du territoire français d'autre part. Les méthodes de mesure sont rapidement expliquées, l'accent est mis sur la signification des nombres obtenus, leur comparaison d'une ville à l'autre et leur évolution au cours du temps.
Disfunción endotelial en territorio arterial en pacientes jóvenes con enfermedad tromboembólica venosa
2015
La enfermedad tromboembólica venosa es la patología vascular más frecuente en gente joven, con 70 casos por cada 100.000 habitantes/año. En los últimos años se ha visto asociada al desarrollo de patología arterial, lo que aumenta aún más su morbimortalidad con una amplia repercusión socioeconómica. Este hecho ha sido objeto de diferentes estudios, sin que los mecanismos por los cuales se produce esta asociación entre patología venosa y arterial hayan sido del todo elucidados, sugiriéndose una etiopatogenia común principalmente basada en el estado inflamatorio que subyace en ambas patologías. Por ello, el objetivo del presente trabajo lo ha constituido el estudio de la inflamación vascular a…
Localisation de la population selon les enchères foncières des ménages dans une aire métropolitaine fractale
2002
International audience