1,868 research outputs found
Lactose as an inexpensive starting material for the preparation of aldohexos-5-uloses: synthesis of L-ribo and D-lyxo derivatives
SUMMARY: Partially protected derivatives of L-ribo- and D-lyxo-aldohexos-5-ulose have been prepared starting from triacetonlactose dimethyl acetal derivatives. Key steps of the synthetic sequences are a) the synthesis of 4'-deoxy-4'-eno- and 6'-deoxy-5'-eno lactose derivatives, and b) the epoxidation-methanolysis of the above enol ethers to give 1,5-bis-glycopyranosides, masked form of the target 1,5-dicarbonyl hexoses
The influence of surface roughness on the rheology of immersed and dry frictional spheres
Pressure-imposed rheometry is used to examine the influence of surface
roughness on the rheology of immersed and dry frictional spheres in the dense
regime. The quasi-static value of the effective friction coefficient is not
significantly affected by particle roughness while the critical volume fraction
at jamming decreases with increasing roughness. These values are found to be
similar in immersed and dry conditions. Rescaling the volume fraction by the
maximum volume fraction leads to collapses of rheological data on master
curves. The asymptotic behaviors are examined close to the jamming transition
Scale-free channeling patterns near the onset of erosion of sheared granular beds
Erosion shapes our landscape and occurs when a sufficient shear stress is
exerted by a fluid on a sedimented layer. What controls erosion at a
microscopic level remains debated, especially near the threshold forcing where
it stops. Here we study experimentally the collective dynamics of the moving
particles, using a set-up where the system spontaneously evolves toward the
erosion onset. We find that the spatial organization of the erosion flux is
heterogeneous in space, and occurs along channels of local flux whose
distribution displays scaling near threshold and follows , where is the mean erosion flux. Channels are strongly correlated
in the direction of forcing but not in the transverse direction. We show that
these results quantitatively agree with a model where the dynamics is governed
by the competition of disorder (which channels mobile particles) and particle
interactions (which reduces channeling). These observations support that for
laminar flows, erosion is a dynamical phase transition which shares similarity
with the plastic depinning transition occurring in dirty superconductors. The
methodology we introduce here could be applied to probe these systems as well.Comment: 8 pages, 6 figure
"rumori e silenzi" l'altra via dei platani
La tesi si pone come obiettivo la progettazione architettonica di un complesso di edifici, strutture e spazi pubblici sito a Calambrone in via dei Platani. Alla progettazione architettonica si aggiunge un approfondimento di analisi e calcolo strutturale
Transition from viscous to inertial regime in dense suspensions
Non-Brownian suspensions present a transition from Newtonian behavior in the
zero-shear limit to a shear thickening behaviour at a large shear rate, none of
which is clearly understood so far. Here, we carry out numerical simulations of
such an athermal dense suspension under shear, at an imposed confining
pressure. This set-up is conceptually identical to the recent experiments of
Boyer and co-workers [Phys. Rev. Lett. 107,188301 (2011)]. Varying the
interstitial fluid viscosities, we recover the Newtonian and Bagnoldian regimes
and show that they correspond to a dissipation dominated by viscous and contact
forces respectively. We show that the two rheological regimes can be unified as
a function of a single dimensionless number, by adding the contributions to the
dissipation at a given volume fraction.Comment: 4 pages, 3 figure
Non-Poisson statistics of settling spheres
International audienceDirect tracking of the particle positions in a sedimenting suspension indicates that the particles are not simply randomly distributed. The initial mixing of the suspension leads to a microstructure which consists of regions devoid of particles surrounded by regions where particles have an excess of close neighbors and which is maintained during sedimentation
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