Search results for " diffusion"
showing 10 items of 521 documents
Microscopic verification of dynamic scaling in dilute polymer solutions: A molecular-dynamics simulation
1991
The dynamics of a single polymer chain immersed in a large number of solvent particles is studied by molecular dynamics. This is the first simulation where chain length (30, 40, and 60 monomers) and statistical accuracy are sufficient to test the predictions of the Zimm model as a result of the particle-particle interactions: The short-time diffusion constant is in good agreement with the Kirkwood prediction, and the monomer motions exhibit the expected dynamic scaling. The long-range hydrodynamic interaction requires a data analysis that explicitly includes the periodic images via Ewald sums.
Anomalous Diffusion and Relaxation of Collapsed Polymer Chains
1994
Time-dependent displacement of monomers and the centre-of-gravity motion of a polymer chain at various temperatures below the theta-temperature are studied by Monte Carlo simulation of an off-lattice model. While inner monomers diffuse Rouse-like, [ri(t) − ri(0)]2 t1/2, the centre of mass exhibits pronounced anomalous diffusion, [rc.m.(t) − rc.m.(0)]2 ta, where the exponent a seems to depend on temperature. The resulting anomalous dependence of the relaxation times on chain length is discussed in terms of scaling ideas. A possible relation to a glasslike freezing in of the collapsed globules is pointed out.
Self-Diffusion of Associating Star-Shaped Polymers
2016
The dynamics of associating bonds in transient polymer networks exerts a paramount influence on their relaxation and time-dependent mechanical properties. In particular, diffusive motion of polymers mediated by the dissociation and association equilibrium of reversible junctions can affect the materials’ structural stability, dynamic mechanical properties, and a broad spectrum of functionality that arises from the constant motion of polymer chains. In this work, forced Rayleigh scattering is used to measure the diffusion of terpyridine end-functionalized four-arm poly(ethylene glycol) polymers transiently interlinked by zinc ions in organic solvent across a wide range of length and time sca…
Factors influencing the transport of tryptophan hydrochloride through supported liquid membranes containing macrocyclic carriers
1997
Commercially available PTFE membranes were used as a support for liquid membranes in amino acid transport. Using tryptophan as a model amino acid, the influence of the type of organic liquid, kind of macrocyclic carrier and counter-ion on transport efficiency was examined. These studies show the strong influence of the kind of the counter-ion co-transported with amino acid cation, and the type of macrocyclic carrier used on the transport efficiency. The transport efficiency depends also on the pH of the source phase and on the nature of the organic liquid used as a membrane solvent. Liquid membranes supported on commercial porous-PTFE-membranes with hydrophobic solvents are stable for more …
AMBIENTE COSTRUITO E SOSTENIBILITÀ – Materiali riciclati e Design for Disassembly tra ricerca e buone pratiche
2020
In the context of environmental emergency of which the construction sector is one of the main causes – since it consumes 40% of the (embodied and operational) energy and produces about a third of the total waste – and due to the ambitious objectives set by the international community and by many countries to reduce the environmental impact of buildings during their whole life cycle, this paper wants to make a contribution to the understanding of the state of the art on cycle-based research activities, sustainable experiments and good practices that the building industry and the academy have implemented in recent years. In particular, it refers to cycle-based theoretical and experimental act…
Protein diffusion, stability and activity in crowded media
2015
Sviluppo di un software per l’analisi di immagini di Diffusion Kurtosis Imaging
2013
L’analisi mediante RM del tensore di diffusione (Diffusion Tensor Imaging, DTI) consente di valutare anche in vivo e con modalità non invasive il processo di diffusione delle molecole d’acqua nei tessuti biologici. La peculiare organizzazione di alcuni tessuti biologici (es: muscoli, sostanza bianca del sistema nervoso centrale e tessuti ad alta cellularità) influenza tale fenomeno rendendolo anisotropo e quindi ben valutabile con tali tecniche di studio. Nonostante i grandi vantaggi di tale tecnica, il DTI è basato su un modello molto semplificato che assume che lo spostamento per diffusione segua un profilo gaussiano il che è molto raro in un ambiente variegato come i tessuti biologic…
The global spread of the concept of cultural policy
2020
The article studies UNESCO's program that, from the late 1960s onward, aimed at spreading globally the concept of cultural policy. An essential part of the program, UNESCO invited member states from different regions of the world to prepare reports on national cultural policy. That was successful in spreading cultural policy as a concept and as a governmental structure. Except for only Australia, Canada and the United States, in which cultural policy is handled at a sub-state level, all countries that produced a national report have established a ministry of culture, typically synchronously with the report. The analysis suggests that UNESCO's success was due to two factors: the process of d…
A study of physical processes in microplasma capillary discharges
2011
We continue the research of low-pressure capillary discharge lamps of 500 μ m in radius in Ar/Hg, Kr/Hg and Xe/Hg mixtures. In the previous paper, an experimental approach which combines the optical emission spectroscopy (OES) and tomographic methods was developed to study the capillary discharge. The present work is focused on interpretation of the tomographic reconstruction results for understanding the physical processes occurring in a capillary plasma. Analyzing the results of reconstruction, it was concluded that the radial profiles of Ar, Kr and Xe emission coefficients are in a good agreement with the Schottky theory. According to the Schottky model, ionization processes in plasma a…