235 research outputs found
Cavitation induced by explosion in a model of ideal fluid
We discuss the problem of an explosion in the cubic-quintic superfluid model,
in relation to some experimental observations. We show numerically that an
explosion in such a model might induce a cavitation bubble for large enough
energy. This gives a consistent view for rebound bubbles in superfluid and we
indentify the loss of energy between the successive rebounds as radiated waves.
We compute self-similar solution of the explosion for the early stage, when no
bubbles have been nucleated. The solution also gives the wave number of the
excitations emitted through the shock wave.Comment: 21 pages,13 figures, other comment
Memory effects in classical and quantum mean-field disordered models
We apply the Kovacs experimental protocol to classical and quantum p-spin
models. We show that these models have memory effects as those observed
experimentally in super-cooled polymer melts. We discuss our results in
connection to other classical models that capture memory effects. We propose
that a similar protocol applied to quantum glassy systems might be useful to
understand their dynamics.Comment: 24 pages, 12 figure
A continuous non-linear shadowing model of columnar growth
We propose the first continuous model with long range screening (shadowing)
that described columnar growth in one space dimension, as observed in plasma
sputter deposition. It is based on a new continuous partial derivative equation
with non-linear diffusion and where the shadowing effects apply on all the
different processes.Comment: Fast Track Communicatio
Shear bands in granular flow through a mixing length model
We discuss the advantages and results of using a mixing-length, compressible
model to account for shear banding behaviour in granular flow. We formulate a
general approach based on two function of the solid fraction to be determined.
Studying the vertical chute flow, we show that shear band thickness is always
independent from flowrate in the quasistatic limit, for Coulomb wall boundary
conditions. The effect of bin width is addressed using the functions developed
by Pouliquen and coworkers, predicting a linear dependence of shear band
thickness by channel width, while literature reports contrasting data. We also
discuss the influence of wall roughness on shear bands. Through a Coulomb wall
friction criterion we show that our model correctly predicts the effect of
increasing wall roughness on the thickness of shear bands. Then a simple
mixing-length approach to steady granular flows can be useful and
representative of a number of original features of granular flow.Comment: submitted to EP
Electrochemical Multi-Tagging of Cysteinyl Peptides during Microspray Mass Spectrometry: Numerical Simulation of Consecutive Reactions in a Microchannel
On-line electrogeneration of mass tags in a microspray emitter is used to quantify the number of cysteine groups in a given peptide. A finite-element simulation of the multi-step process yields the relative distribution and concentration of tags, untagged and tagged species in the microchannel before the spray event. The work focuses on the tagging of cysteine moieties in peptides or proteins by electrogenerated quinone mass probes. The main chemical parameters determining the kinetics of the labelling are assessed and discussed considering the microfluidic aspects of the process. The control of the tagging extent allows the simultaneous MS analysis of both the unmodified and modified peptide(s). The number of cysteine groups corresponds to the number of characteristic mass shifts observed from the unmodified peptide. The present theoretical work establishes the range of optimum conditions for the determination of the number of cysteine groups in peptides containing up to five cysteine groups
Sandwich mixerâreactor: influence of the diffusion coefficient and flow rate ratios
A sandwich mixer consists of mixing two solutions in a channel, one central laminar flow being sandwiched between two outer flow solutions. The present numerical study considers the convectionâ diffusion of two reacting species A and B, provided respectively by the two incoming solutions. The simulations show how the diffusion coefficient, flow rate and species concentration ratios influence, via the transversal diffusion length and reaction kinetics, the reaction extent at the end of the sandwich mixer. First, this extent can be enhanced up to 60% if the species with the lowest diffusion coefficient is located in the outer solutions where the flow velocity is small compared to that of the central part (higher residence time). Secondly, decreasing the outer flow rates (to confine the reaction close to the walls) and increasing the local concentration to keep the same flux ratio improve the extent by 300%. Comparison with a bi-lamination passive mixer, with an ideal mixer and an electro-osmotic driven flow mixer is presented. These conclusions are also demonstrated for consecutive reactions, showing an amplification of the effects described above. The results are also presented versus the residence time in the mixerâreactor to show the time window for which the gain is appreciable
Creep motion in a granular pile exhibiting steady surface flow
We investigate experimentally granular piles exhibiting steady surface flow.
Below the surface flow, it has been believed exisitence of a `frozen' bulk
region, but our results show absence of such a frozen bulk. We report here that
even the particles in deep layers in the bulk exhibit very slow flow and that
such motion can be detected at an arbitrary depth. The mean velocity of the
creep motion decays exponentially with depth, and the characteristic decay
length is approximately equal to the particle-size and independent of the flow
rate. It is expected that the creep motion we have seeen is observable in all
sheared granular systems.Comment: 3 pages, 4 figure
Protein adsorption in static microsystems: effect of the surface to volume ratio
A numerical model for the adsorption kinetics of proteins on the walls of a microchannel has been developed using the finite element method (FEM) to address the coupling with diffusion phenomena in the restricted microchannel volume. Time evolutions of the concentration of one species are given, both in solution and on the microchannel walls. The model illustrates the adsorption limitation sometimes observed when the microdimensions of these systems induce a global depletion of the bulk solution. A new non-dimensional parameter is introduced to predict the final value of the coverage of any microsystem under static adsorption. A working curve and a criteria (h/KÎmax > 10) are provided in order to choose, for given adsorption characteristics, the value of the volume-to-surface ratio (i.e. the channel height h) avoiding depletion effects on the coverage (relative coverage greater than 90% of the theoretical one). Simulations were compared with confocal microscopy measurements of IgG antibody adsorption on the walls of a PET microchannel. The fit of the model to the experimental data show that the adsorption is under apparent kinetic control
Dynamic protein adsorption in microchannels by "stop-flow" and continuous flow
This work addresses two ways of loading proteins on microchannel surfaces for immunoassay applications: the âstop-flowâ and the continuous flow processes. The âstop-flowâ method consists of successive static incubation periods where the bulk solution depletes upon the adsorption process. In the present paper, a multi-step âstop-flowâ protein coating is studied and compared to a coating under continuous flow conditions. For the âstop-flowâ, a non-dimensional parameter is here introduced, indicating the adsorbing capacity of the system, by which it is possible to calculate the number of loads necessary to reach the optimum coverage. For the continuous flow, the effects on the adsorption of the kinetic rates, flow velocity and wall capacity have been considered. This study shows the importance of a careful choice of the fluid velocity to minimise the sample waste. For diffusion controlled and kinetics controlled processes, two flow velocity criteria are provided in order to obtain the best possible coverage, with the same amount of sample as with the âstop-flowâ
Response properties in a model for granular matter
We investigate the response properties of granular media in the framework of
the so-called {\em Random Tetris Model}. We monitor, for different driving
procedures, several quantities: the evolution of the density and of the density
profiles, the ageing properties through the two-times correlation functions and
the two-times mean-square distance between the potential energies, the response
function defined in terms of the difference in the potential energies of two
replica driven in two slightly different ways. We focus in particular on the
role played by the spatial inhomogeneities (structures) spontaneously emerging
during the compaction process, the history of the sample and the driving
procedure. It turns out that none of these ingredients can be neglected for the
correct interpretation of the experimental or numerical data. We discuss the
problem of the optimization of the compaction process and we comment on the
validity of our results for the description of granular materials in a
thermodynamic framework.Comment: 22 pages, 35 eps files (21 figures
- âŠ