Bifurcations in the theory of current transfer to cathodes of dc discharges and observations of transitions between different modes

General scenarios of transitions between different spot patterns on electrodes of dc gas discharges and their relation to bifurcations of steady-state solutions are analyzed. In the case of cathodes of arc discharges, it is shown that any transition between different modes of current transfer is related to a bifurcation of steady-state solutions. In particular, transitions between diffuse and spot modes on axially symmetric cathodes, frequently observed in the experiment, represent an indication of the presence of pitchfork or fold bifurcations of steady-state solutions. Experimental observations of transitions on cathodes of dc glow microdischarges are analyzed and those potentially related to bifurcations of steady-state solutions are identified. The relevant bifurcations are investigated numerically and the computed patterns are found to conform to those observed in the course of the corresponding transitions in the experiment

Synthesis of linear, double chain, ladder polymers from substituted tetraphosphonitriles Quarterly report, Sep. - Nov. 1966

Synthesis of linear, double chain ladder polymers from substituted tetraphosphonitrile

Synthesis of linear, double chain, ladder polymers from substituted tetraphosphonitriles Quarterly progress report, Sep. - Nov. 1966

Synthesis of linear, double chain, ladder polymers from substituted tetraphosphonitrile

TIES 20: Relative Binding Free Energy with a Flexible Superimposition Algorithm and Partial Ring Morphing

The TIES (Thermodynamic Integration with Enhanced Sampling) protocol is a formally exact alchemical approach in computational chemistry to the calculation of relative binding free energies. The validity of TIES relies on the correctness of matching atoms across compared pairs of ligands, laying the foundation for the transformation along an alchemical pathway. We implement a flexible topology superimposition algorithm which uses an exhaustive joint-traversal for computing the largest common component(s). The algorithm is employed to enable matching and morphing of partial rings in the TIES protocol along with a validation study using 55 transformations and five different proteins from our previous work. We find that TIES 20 with the RESP charge system, using the new superimposition algorithm, reproduces the previous results with mean unsigned error of 0.75 kcal/mol with respect to the experimental data. Enabling the morphing of partial rings decreases the size of the alchemical region in the dual-topology transformations resulting in a significant improvement in the prediction precision. We find that increasing the ensemble size from 5 to 20 replicas per λ window only has a minimal impact on the accuracy. However, the non-normal nature of the relative free energy distributions underscores the importance of ensemble simulation. We further compare the results with the AM1-BCC charge system and show that it improves agreement with the experimental data by slightly over 10%. This improvement is partly due to AM1-BCC affecting only the charges of the atoms local to the mutation, which translates to even fewer morphed atoms, consequently reducing issues with sampling and therefore ensemble averaging. TIES 20, in conjunction with the enablement of ring morphing, reduces the size of the alchemical region and significantly improves the precision of the predicted free energies

Modelling cathode spots in glow discharges in the cathode boundary layer geometry

Self-organized patterns of cathode spots in glow discharges are computed in the cathode boundary layer geometry, which is the one employed in most of the experiments reported in the literature. The model comprises conservation and transport equations of electrons and a single ion species, written in the drift-diffusion and local-field approximations, and Poisson’s equation. Multiple solutions existing for the same value of the discharge current and describing modes with different configurations of cathode spots are computed by means of a stationary solver. The computed solutions are compared to their counterparts for plane-parallel electrodes, and experiments. All of the computed spot patterns have been observed in the experiment.info:eu-repo/semantics/publishedVersio

Modelling excited species and their role on kinetic pathways in the non-oxidative coupling of methane by dielectric barrier discharge

Acknowledgments We acknowledge and greatly appreciate the assistance from Dr. Mihailova from Plasma Matters B.V. in working with the software Plasimo and from Dr Marcus Campbell Bannerman from the University of Aberdeen for providing access to the computational cluster used for carrying out the simulations in this work. The work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) New Investigator Award, grant no. EP/R031800/1.Peer reviewedPostprin

Collisional Redistribution Of Polarized Radiation For Sr-ar(He) Systems: A Numerical Comparison Of The Semiclassical Decoupiing/locking Model To Exact Results

Abstract Semiclassical formulations of collisional redistribution of polarized radiation are presented at several levels of approximation, from full classical path coupled equations to the backing/decoupling model. These are numerically tested against the results of a quantum mechanical coupled-channels formalism, by the comparison of polarization curves in both spectral wings of the Srf1 So-1 Pi) transition, with Ar and He as collisional perturbers. It is found that the locking/decoupling model can often produce good agreement with exact results if the effects due to trajectories and multiple Condon points are treated properly. Significant discrepancies due to the Condon approximation used ty the model is seen in the near blue wing of the spectra and attributed to antistatic effects. A clear analysis of these effects and the role of ambiguities introduced ty the backing/decoupling radius is possible ty a comparison with classical path methods in which the effects of radiative coupling and of rotational decoupling can be tested separately with a high degree of accuracy. © 1991 IOP Publishing Ltd

3D modelling of self-organized patterns of spots on anodes of DC glow discharge

Self-organized patterns of spots on a at metallic anode in a cylindrical glow dis- charge tube are simulated self-consistently. A standard model of a glow discharge is used, comprising conservation and transport equations for a single species of ion and electrons, written with the use of the drift-diffusion and local-field approximations, and the Poisson equation. The computation domain is the region from the anode to the discharge column; only processes in the near-anode region are considered. Multiple solutions, existing in the same range of discharge current and describing modes with and without anode spots, are computed by means of a stationary solver. The computed spots exhibited unexpected behavior. A reversal of the local anode current density in the middle of each of the spots was found, i.e. mini-cathodes are formed inside the spots. The solutions do not fit into the conventional pattern of self-organization in bistable nonlinear dissipative systems; e.g. the modes are not joined by bifurcations

Plasma-enhanced catalysis for the upgrading of methane : A review of modelling and simulation methods

The work was supported by the UK Engineering and Physical Sciences Research Council (EPSRC) New Investigator Award, grant no. EP/R031800/1.Peer reviewedPostprin

TIES 2.0: A dual-topology open source relative binding free energy builder with web portal

Relative binding free energy (RBFE) calculations are widely used to aid the process of drug discovery. TIES, Thermodynamic Integration with Enhanced Sampling, is a dual-topology approach to RBFE calculations with support for NAMD and OpenMM molecular dynamics engines. The software has been thoroughly validated on publicly available datasets. Here we describe the open source software along with a web portal (https://ccs-ties.org) that enables users to perform such calculations correctly and rapidly