Search results for "Diffusion"

1987

Diffusion coefficients D of singly and doubly end-labeled polystyrenes (PS) with molecular weights in the range 6500 ≤ M ≤ 75400 were measured in a PS matrix of molecular weight M′ = 111000, and in matrices with M′ = M. At 212°C, we find no influence of the label. In a power-law description D = D0 · M−α · M′−β we find α = 2,0 for M′ = 111000 and α + β = 2,4 for M = M′. The crossover to Rouse-like behavior for short-M chains is at Me ≈ 18000 for the former (high M′), and at Mc ≈ 33000 in the latter (M′ = M) case. At 185°C, we find a more complex scaling behavior and different D values for singly and doubly labeled PS.

1984

Dissolution de polystyrene marque par de la fluorescence dans une matrice de masse moleculaire moyenne en poids de 110000

Diffusion of digital culture: analysis of the Internet forum of a MOOC

2017

When MOOCs are increasing all over the world as a mean for improving the diffusion of culture and science, it is interesting to observe how those MOOCS build communities of knowledge, and which is the impact of those communities on the acquisition of knowledge. In this article, we present the principles of design of the MOOC Digital & Culture Writing that aims to spread digital culture. Then, we analyse the messages posted on forums by the related community, and the cognitive process to which they refer. Posts analysis reveals reflexivity processes when participants are writing on forums. It appears that reflexivity cognitive processes are at the heart of both social interaction and digital…

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…

Modeling long-range memory with stationary Markovian processes

2009

In this paper we give explicit examples of power-law correlated stationary Markovian processes y(t) where the stationary pdf shows tails which are gaussian or exponential. These processes are obtained by simply performing a coordinate transformation of a specific power-law correlated additive process x(t), already known in the literature, whose pdf shows power-law tails 1/x^a. We give analytical and numerical evidence that although the new processes (i) are Markovian and (ii) have gaussian or exponential tails their autocorrelation function still shows a power-law decay =1/T^b where b grows with a with a law which is compatible with b=a/2-c, where c is a numerical constant. When a<2(1+c) th…

Protein diffusion, stability and activity in crowded media

2015

Characterization of spatial porosity and mineral distribution of crystalline rock using X-ray micro computed tomography, C-14-PMMA autoradiography an…

2019

The spatial porosity and mineral distribution of geological materials strongly affects transport processes in them. X-ray micro computed tomography (X-mu CT) has proven to be a powerful tool for characterizing the spatial mineral distribution of geological samples in 3-D. However, limitations in resolution prevent an accurate characterization of pore space especially for tight crystalline rock samples and 2-D methods such as C-14-polymethylmethacrylate (C-14-PMMA) autoradiography and scanning electron microscopy (SEM) are needed. The spatial porosity and mineral distributions of tight crystalline rock samples from Aspo, Sweden, and Olkiluoto, Finland, were studied here. The X-mu CT were use…

Le rôle des périodiques dans la diffusion du savoir médical en France et en Grande-Bretagne (fin XVIIe-XVIIIe siècles)

2010

Garnet as a monitor for melt–rock interaction: Textural, mineralogical, and compositional evidence of partial melting and melt‐driven metasomatism

2021

International audience; In this study, we focus on a partially melted garnet-bearing granulite from the Salvador–Esplanade Belt (Salvador da Bahia, Brazil), and examine the behaviour of major and trace elements during partial melting and melt-driven metasomatism. Phase equilibria modelling and U–Th– Pb geochronology show that the sample underwent partial melting during the heating segment of the decompression path from ~1.2 GPa and 675–700° C to ~0.8 GPa and 790°C at c. 2.06 Ga. During the final stage of decompression, from 0.8 to ~0.5 GPa, physical segregation of melt resulted in the establishment of chemical potential gradients and mass transfer between the host granulite and the leucosom…

A study of VUV emission and the extracted electron-ion ratio in hydrogen and deuterium plasmas of a filament-driven H−/D− ion source

2019

Vacuum ultraviolet (VUV) emission diagnostics for studying differences of electron impact processes in hydrogen and deuterium plasmas are presented. The method is applied to study a filament driven multicusp arc discharge negative ion source by comparing the VUV-emission intensities of different emission bands and extracted currents of H−/D− ions and electrons. It was found that the ratio of coextracted electrons to extracted ions is four times higher for deuterium than for hydrogen. No significant differences of the VUV-spectra or volumetric rates of ionization, excitation, production of high vibrational states, and dissociation were found between the plasmas of the two isotopes. The volum…