Critical behaviour of the Rouse model for gelling polymers

It is shown that the traditionally accepted "Rouse values" for the critical exponents at the gelation transition do not arise from the Rouse model for gelling polymers. The true critical behaviour of the Rouse model for gelling polymers is obtained from spectral properties of the connectivity matrix of the fractal clusters that are formed by the molecules. The required spectral properties are related to the return probability of a "blind ant"-random walk on the critical percolating cluster. The resulting scaling relations express the critical exponents of the shear-stress-relaxation function, and hence those of the shear viscosity and of the first normal stress coefficient, in terms of the spectral dimension $d_{s}$ of the critical percolating cluster and the exponents $\sigma$ and $\tau$ of the cluster-size distribution.Comment: 9 pages, slightly extended version, to appear in J. Phys.

Elasticity of Gaussian and nearly-Gaussian phantom networks

We study the elastic properties of phantom networks of Gaussian and nearly-Gaussian springs. We show that the stress tensor of a Gaussian network coincides with the conductivity tensor of an equivalent resistor network, while its elastic constants vanish. We use a perturbation theory to analyze the elastic behavior of networks of slightly non-Gaussian springs. We show that the elastic constants of phantom percolation networks of nearly-Gaussian springs have a power low dependence on the distance of the system from the percolation threshold, and derive bounds on the exponents.Comment: submitted to Phys. Rev. E, 10 pages, 1 figur

Improvement of pyclen-based manganese complexes relaxivity by using polymersome vesicles

NANOPARTICULES D'OXYDE DE FER OU DE MANGANÈSE DENDRONISÉES POUR L'IRM - Fédération Wallonie Bruxelle

Firm's Evaluation of Location Quality: Evidence from East Germany

Our study provides evidence for firms' evaluation of location quality. We use a 2004 survey of 6,000 East German firms that contained questions on the importance and assessment of 15 different location factors ranging from closeness to customers and suppliers, transport infrastructure, and proximity to research institutions and universities, as well as questions about the local financial institutions and region's 'image'. The results show (1) a great deal of heterogeneity in terms of which firm- or regional-level characteristics are important in the evaluation of a specific location factor, (2) that the model's explanatory power is, overall, low and thus neither location characteristics nor internal factors are fully reflected in the perceptions, (3) that a firm's business situation and whether a location factor is considered important have explanatory power for perception. One policy-relevant conclusion that we derive from these findings is that location policy should consider firms' perception of a specific location in addition to improving the actual attributes of that location

Effect of ZrO₂ on the glass durability

ABSTRACTBorosilicate glasses were prepared with the molar composition 70 SiO2-15 Na2O-15B2O3-n ZrO2 with n ranging from 0 to 10. The glasses were studied by conventional static dissolution tests of powders at 90°C in pure water and in buffered solutions for long times (months) and short times (minutes). During the first minutes of alteration in a buffered solution, sodium is rapidly leached until its loss becomes controlled by the silicon hydrolysis. The experimental data show that the introduction of zirconium drastically reduces the initial dissolution rate (Vo) of the glass. Zirconium strengthens the silica network but also strongly modifies the porous layer morphology. In the case of glasses with small Zr contents (less than 2%), the silica dissolution rate decreases but the formation of a passivating alteration layer is also delayed. As a result, small amounts of zirconium paradoxically decrease the loss of silica but increase the final loss of sodium and boron in the static leaching tests. Larger zirconium contents (above 5%) increase the durability of the glass regarding the initial dissolution rate and the final concentration of all elements.</jats:p