92 research outputs found
Phase transition in the two-component symmetric exclusion process with open boundaries
We consider single-file diffusion in an open system with two species of
particles. At the boundaries we assume different reservoir densities which
drive the system into a non-equilibrium steady state. As a model we use an
one-dimensional two-component simple symmetric exclusion process with two
different hopping rates and open boundaries. For investigating the
dynamics in the hydrodynamic limit we derive a system of coupled non-linear
diffusion equations for the coarse-grained particle densities. The relaxation
of the initial density profile is analyzed by numerical integration. Exact
analytical expressions are obtained for the self-diffusion coefficients, which
turns out to be length-dependent, and for the stationary solution. In the
steady state we find a discontinuous boundary-induced phase transition as the
total exterior density gradient between the system boundaries is varied. At one
boundary a boundary layer develops inside which the current flows against the
local density gradient. Generically the width of the boundary layer and the
bulk density profiles do not depend on the two hopping rates. At the phase
transition line, however, the individual density profiles depend strongly on
the ratio . Dynamic Monte Carlo simulation confirm our theoretical
predictions.Comment: 26 pages, 6 figure
Amplification of Molecular Traffic Control in catalytic grains with novel channel topology design
We investigate the conditions for reactivity enhancement of catalytic
processes in porous solids by use of molecular traffic control (MTC). With
dynamic Monte-Carlo simulations and continuous-time master equation theory
applied to the high concentration regime we obtain a quantitative description
of the MTC effect for a network of intersecting single-file channels in a wide
range of grain parameters and for optimal external operating conditions.
Implementing the concept of MTC in models with specially designed alternating
bimodal channels we find the efficiency ratio (compared with a topologically
and structurally similar reference system without MTC) to be enhanced with
increasing grain diameter, a property verified for the first time for an MTC
system. Even for short intersection channels, MTC leads to a reactivity
enhancement of up to approximately 65%. This suggests that MTC may
significantly enhance the efficiency of a catalytic process for small as well
as large porous particles with a suitably chosen binary channel topology.Comment: 15 pages, 12 figure
Amplication of Molecular Traffic Control in catalytic grains with novel channel topology design
We investigate the conditions for reactivity enhancement of catalytic processes in porous solids by the use of molecular traffic control (MTC). With dynamic Monte-Carlo simulations and continuous-time master equation theory applied to the high concentration regime, we obtain a quantitative description of the MTC effect for a network of intersecting single-file channels in a wide range of grain parameters and for optimal external operating conditions. Implementing the concept of MTC in models with specially designed alternating bimodal channels, we find the efficiency ratio (compared with a topologically and structurally similar reference system without MTC) to be enhanced with increasing grain diameter, a property verified for the first time for a MTC system. Even for short intersection channels, MTC leads to a reactivity enhancement of up to approximately 65%. This suggests that MTC may significantly enhance the efficiency of a catalytic process for small as well as large porous particles with a suitably chosen binary channel topology
Boundary-induced bulk phase transition and violation of Fick's law in two-component single-file diffusion with open boundaries
We study two-component single-file diffusion inside a narrow channel that at
its ends is open and connected with particle reservoirs. Using a two-species
version of the symmetric simple exclusion process as a model, we propose a
hydrodynamic description of the coarse-grained dynamics with a self-diffusion
coefficient that is inversely proportional to the length of the channel. The
theory predicts an unexpected nonequilibrium phase transition for the bulk
particle density as the external total density gradient between the reservoirs
is varied. The individual particle currents do not in general satisfy Fick's
first law. These results are confirmed by extensive dynamical Monte-Carlo
simulations for equal diffusivities of the two components.Comment: 12 pages, 3 figure
Molecular Traffic Control in a 3D network of single file channels and fast reactivity
We study the conditions for reactivity enhancement of catalytic processes in
porous solids by use of molecular traffic control (MTC) as a function of grain
size. We extend a recently introduced two dimensional model system to three
dimensions. With dynamic Monte-Carlo simulations and analytical solution of the
associated Master equation we obtain a quantitative description of the MTC
effect in the limit of fast reactivity. The efficiency ratio (compared with a
topologically and structurally similar reference system without MTC) is
inversely proportional to the grain diameter.Comment: corrected affiliatio
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“It’s Always Good to Ask”:A Mixed Methods Study on the Perceived Role of Sexual Health Practitioners Asking Gay and Bisexual Men About Experiences of Domestic Violence and Abuse
Development of joint displays is a valued approach to merging qualitative and quantitative findings in mixed methods research. This study aimed to illustrate a case series mixed methods display and the utility of using mixed methods for broadening our understanding of domestic violence and abuse. Using a convergent design, 532 gay and bisexual men participated in a Health and Relationship Survey in a U.K. sexual health service and 19 in an interview. Quantitative and qualitative data were analyzed separately and integrated at the level of interpretation and reporting. There were inconsistencies in perceptions and reports of abuse. Men were supportive of selective enquiry for domestic violence and abuse by practitioners (62.6%; 95% confidence interval = 58.1% to 66.7%) while being mindful of contextual factors.</p
“It’s always good to ask”: a mixed methods study on the perceived role of sexual health practitioners asking gay and bisexual men about experiences of domestic violence and abuse
Development of joint displays is a valued approach to merging qualitative and quantitative findings in mixed methods research. This study aimed to illustrate a case series mixed methods display and the utility of using mixed methods for broadening our understanding of domestic violence and abuse. Using a convergent design, 532 gay and bisexual men participated in a Health and Relationship Survey in a U.K. sexual health service and 19 in an interview. Quantitative and qualitative data were analyzed separately and integrated at the level of interpretation and reporting. There were inconsistencies in perceptions and reports of abuse. Men were supportive of selective enquiry for domestic violence and abuse by practitioners (62.6%; 95% confidence interval = 58.1% to 66.7%) while being mindful of contextual factors
Particle current in symmetric exclusion process with time-dependent hopping rates
In a recent study, (Jain et al 2007 Phys. Rev. Lett. 99 190601), a symmetric
exclusion process with time-dependent hopping rates was introduced. Using
simulations and a perturbation theory, it was shown that if the hopping rates
at two neighboring sites of a closed ring vary periodically in time and have a
relative phase difference, there is a net DC current which decreases inversely
with the system size. In this work, we simplify and generalize our earlier
treatment. We study a model where hopping rates at all sites vary periodically
in time, and show that for certain choices of relative phases, a DC current of
order unity can be obtained. Our results are obtained using a perturbation
theory in the amplitude of the time-dependent part of the hopping rate. We also
present results obtained in a sudden approximation that assumes large
modulation frequency.Comment: 17 pages, 2 figure
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