scholarly journals Coexisting multi-states in catalytic hydrogen oxidation on rhodium

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
P. Winkler ◽  
J. Zeininger ◽  
M. Raab ◽  
Y. Suchorski ◽  
A. Steiger-Thirsfeld ◽  
...  
Keyword(s):  
Steady State ◽  
Hydrogen Oxidation ◽  
Kinetic Modelling ◽  
Mean Field ◽  
Photoemission Spectroscopy ◽  
Spatially Resolved ◽  
Catalytically Active ◽  
Catalytic Hydrogen ◽  
Experimental Findings ◽  
General Possibility

AbstractCatalytic hydrogen oxidation on a polycrystalline rhodium foil used as a surface structure library is studied by scanning photoelectron microscopy (SPEM) in the 10−6 mbar pressure range, yielding spatially resolved X-ray photoemission spectroscopy (XPS) measurements. Here we report an observation of a previously unknown coexistence of four different states on adjacent differently oriented domains of the same Rh sample at the exactly same conditions. A catalytically active steady state, a catalytically inactive steady state and multifrequential oscillating states are simultaneously observed. Our results thus demonstrate the general possibility of multi-states in a catalytic reaction. This highly unusual behaviour is explained on the basis of peculiarities of the formation and depletion of subsurface oxygen on differently structured Rh surfaces. The experimental findings are supported by mean-field micro-kinetic modelling. The present observations raise the interdisciplinary question of how self-organising dynamic processes in a heterogeneous system are influenced by the permeability of the borders confining the adjacent regions.

scholarly journals Modules or Mean-Fields?

Entropy ◽  
2020 ◽  
Vol 22 (5) ◽  
pp. 552 ◽  
Author(s):  
Thomas Parr ◽  
Noor Sajid ◽  
Karl J. Friston
Keyword(s):  
Steady State ◽  
Message Passing ◽  
Mean Field Theory ◽  
Functional Anatomy ◽  
Mean Field ◽  
State Density ◽  
Stochastic Dynamical Systems ◽  
Conditional Independency ◽  
The Brain ◽  
Non Equilibrium

The segregation of neural processing into distinct streams has been interpreted by some as evidence in favour of a modular view of brain function. This implies a set of specialised ‘modules’, each of which performs a specific kind of computation in isolation of other brain systems, before sharing the result of this operation with other modules. In light of a modern understanding of stochastic non-equilibrium systems, like the brain, a simpler and more parsimonious explanation presents itself. Formulating the evolution of a non-equilibrium steady state system in terms of its density dynamics reveals that such systems appear on average to perform a gradient ascent on their steady state density. If this steady state implies a sufficiently sparse conditional independency structure, this endorses a mean-field dynamical formulation. This decomposes the density over all states in a system into the product of marginal probabilities for those states. This factorisation lends the system a modular appearance, in the sense that we can interpret the dynamics of each factor independently. However, the argument here is that it is factorisation, as opposed to modularisation, that gives rise to the functional anatomy of the brain or, indeed, any sentient system. In the following, we briefly overview mean-field theory and its applications to stochastic dynamical systems. We then unpack the consequences of this factorisation through simple numerical simulations and highlight the implications for neuronal message passing and the computational architecture of sentience.

ChemInform Abstract: Dihydrogen Complexes of Metalloporphyrins: Characterization and Catalytic Hydrogen Oxidation Activity.

ChemInform ◽  
2010 ◽  
Vol 23 (44) ◽  
pp. no-no
Author(s):  
J. P. COLLMAN ◽  
P. S. WAGENKNECHT ◽  
J. E. HUTCHISON ◽  
N. S. LEWIS ◽  
M. A. LOPEZ ◽  
...  
Keyword(s):  
Hydrogen Oxidation ◽  
Oxidation Activity ◽  
Dihydrogen Complexes ◽  
Catalytic Hydrogen

scholarly journals Condensates in thin-layer turbulence

2019 ◽  
Vol 864 ◽  
pp. 490-518 ◽  
Author(s):  
Adrian van Kan ◽  
Alexandros Alexakis
Keyword(s):  
Steady State ◽  
Layer Thickness ◽  
Turbulent Flows ◽  
Mean Field ◽  
Direct Numerical Simulations ◽  
Thin Layers ◽  
Scale Model ◽  
Two Dimensional ◽  
Critical Height ◽  
Basic Features

We examine the steady state of turbulent flows in thin layers using direct numerical simulations. It is shown that when the layer thickness is smaller than a critical height, an inverse cascade arises which leads to the formation of a steady state condensate where most of the energy is concentrated in the largest scale of the system. For layers of thickness smaller than a second critical height, the flow at steady state becomes exactly two-dimensional. The amplitude of the condensate is studied as a function of layer thickness and Reynolds number. Bi-stability and intermittent bursts are found close to the two critical points. The results are interpreted based on a mean-field three-scale model that reproduces some of the basic features of the numerical results.

My Modeling Nanocluster Formation During Ion Beam Synthesis

2009 ◽  
Vol 1181 ◽  
Author(s):  
Chun-Wei Yuan ◽  
Diana O. Yi ◽  
Ian D. Sharp ◽  
Swanee J. Shin ◽  
Christopher Y. Liao ◽  
...  
Keyword(s):  
Steady State ◽  
Cluster Size ◽  
Kinetic Monte Carlo ◽  
Ion Beam ◽  
Effective Diffusion ◽  
Mean Field ◽  
Interface Energy ◽  
Rate Equations ◽  
Ion Beam Synthesis ◽  
State Regime

AbstractIon beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict a steady-state shape for the cluster size distribution that depends only on a characteristic length determined by the ratio of the effective diffusion coefficient times the effective solubility to the ion flux. The average cluster size in the steady state regime is determined by the implanted species/matrix interface energy.

Oxidative Activity of Hydrogen on Nickel and Inconel

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
Kimberly N. Urness ◽  
G. Barney Ellison ◽  
John W. Daily
Keyword(s):  
Stainless Steel ◽  
Reaction Mechanism ◽  
Hydrogen Oxidation ◽  
Surface Oxidation ◽  
Flow Conditions ◽  
Kinetic Reaction ◽  
Tubular Reactors ◽  
Catalytically Active ◽  
Flame Flashback ◽  
Infrared Diagnostics

Experiments were carried out to determine whether nickel or Inconel are catalytically active for hydrogen oxidation. The work was motivated by the problem of flame flashback and/or inlet preignition in hydrogen-rich syngas fueled premixed/prevaporized gas turbine combustors. The experiments were performed using small resistively heated tubular reactors with matrix isolation/infrared diagnostics. Reactors were manufactured from stainless steel, nickel and Inconel. For the flow conditions studied, the conversion efficiency was about 3% for the nickel reactor and 0.9% for the Inconel reactor. No activity was seen for stainless steel. Comparison with a published surface kinetic reaction mechanism for nickel suggests that the surface oxidation rate of H2 in our reactors is about two orders of magnitude less than for specially prepared surfaces.

A Study of Spatially-Resolved Non-Equilibrium in Laser-Irradiated Graphene Using Boltzmann Transport Equation

2013 ◽  
Author(s):  
Ajit K. Vallabhaneni ◽  
James Loy ◽  
Dhruv Singh ◽  
Xiulin Ruan ◽  
Jayathi Murthy
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Laser Irradiation ◽  
Density Functional ◽  
Boltzmann Transport ◽  
Energy Carriers ◽  
Spatially Resolved ◽  
Scattering Rate ◽  
Phonon Generation ◽  
Non Equilibrium

Raman spectroscopy is typically used to characterize graphene in experiments and also to measure properties like thermal conductivity and optical phonon lifetime. The laser-irradiation processes underlying this measurement technique include coupling between photons, electrons and phonons. Recent experimental studies have shown that e-ph scattering limits the performance of graphene-based electronic devices due to the difference in their timescales of relaxation resulting in various bottleneck effects. Furthermore, recently published thermal conductivity measurements on graphene are sensitive to the laser spot size which strengthens the possibility of non-equilibrium between various phonon groups. These studies point to the need to study the spatially-resolved non-equilibrium between various energy carriers in graphene. In this work, we demonstrate non-equilibrium in the e-ph interactions in graphene by solving the linearized electron and phonon Boltzmann transport equations (BTE) iteratively under steady state conditions. We start by assuming that all the electrons equilibrate rapidly to an elevated temperature under laser-irradiation and they gradually relax by phonon emission and reach a steady state. The electron and phonon BTEs are coupled because the e-ph scattering rate depends on the phonon population while the rate of phonon generation depends on the e-ph scattering rate. We used density-functional theory/density-functional perturbation theory (DFT/DFPT) to calculate the electronic eigen states, phonon frequencies and the e-ph coupling matrix elements. We calculated the rate of energy loss from the hot electrons in terms of the phonon generation rate (PGR) which serve as an input for solving the BTE. Likewise, ph-ph relaxation times are calculated from the anharmonic lattice dynamics (LD)/FGR. Through our work, we obtained the spatially resolved temperature profiles of all the relevant energy carriers throughout the entire domain; these are impossible to obtain through experiments.

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