Dielectric-barrier discharges in two-dimensional lattice potentials

We use a pin-grid electrode to introduce a corrugated electrical potential into a planar dielectric-barrier discharge (DBD) system, so that the amplitude of the applied electric field has the profile of a two-dimensional square lattice. The lattice potential provides a template for the spatial distribution of plasma filaments in the system and has pronounced effects on the patterns that can form. The positions at which filaments become localized within the lattice unit cell vary with the width of the discharge gap. The patterns that appear when filaments either overfill or under-fill the lattice are reminiscent of those observed in other physical systems involving 2d lattices. We suggest that the connection between lattice-driven DBDs and other areas of physics may benefit from the further development of models that treat plasma filaments as interacting particles.Comment: 4 pages, 4 figure

Self-organization patterns in electroluminescence of bistable ZnS:Mn thin-film structures

An overview of recent original results concerning self-organized pattern formation in the emission of bistable alternating current ZnS:Mn thin - film electroluminescent structures (TFELS) as a dissipative system is given. The influence of technological factors, affecting the properties TFELS, and driving conditions on both the patterns and the hysteresis of the charge- voltage dependence that is responsible for bistability of the TFELS are considered. The correlation between patterns and the shape of the hysteresis is analyzed. The physical processes with positive and negative feedback, which serve, respectively, as activator and inhibitor in the given dissipative system, are discussed

Transition from Townsend to glow discharge: subcritical, mixed or supercritical

The full parameter space of the transition from Townsend to glow discharge is investigated numerically in one space dimension in the classical model: with electrons and positive ions drifting in the local electric field, impact ionization by electrons ($\alpha$ process), secondary electron emission from the cathode ($\gamma$ process) and space charge effects. We also perform a systematic analytical small current expansion about the Townsend limit up to third order in the total current that fits our numerical data very well. Depending on $\gamma$ and system size pd, the transition from Townsend to glow discharge can show the textbook subcritical behavior, but for smaller values of pd, we also find supercritical or some intermediate ``mixed'' behavior. The analysis in particular lays the basis for understanding the complex spatio-temporal patterns in planar barrier discharge systems.Comment: 12 pages, 10 figures, submitted to Phys. Rev.

Active Learning for Auditory Hierarchy

Much audio content today is rendered as a static stereo mix: fundamentally a fixed single entity. Object-based audio envisages the delivery of sound content using a collection of individual sound ‘objects’ controlled by accompanying metadata. This offers potential for audio to be delivered in a dynamic manner providing enhanced audio for consumers. One example of such treatment is the concept of applying varying levels of data compression to sound objects thereby reducing the volume of data to be transmitted in limited bandwidth situations. This application motivates the ability to accurately classify objects in terms of their ‘hierarchy’. That is, whether or not an object is a foreground sound, which should be reproduced at full quality if possible, or a background sound, which can be heavily compressed without causing a deterioration in the listening experience. Lack of suitably labelled data is an acknowledged problem in the domain. Active Learning is a method that can greatly reduce the manual effort required to label a large corpus by identifying the most effective instances to train a model to high accuracy levels. This paper compares a number of Active Learning methods to investigate which is most effective in the context of a hierarchical labelling task on an audio dataset. Results show that the number of manual labels required can be reduced to 1.7% of the total dataset while still retaining high prediction accuracy

Using a modified Delphi methodology to gain consensus on the use of dressings in chronic wounds management

Objective: Managing chronic wounds is associated with a burden to patients, caregivers, health services and society and there is a lack of clarity regarding the role of dressings in improving outcomes. This study aimed to provide understanding on a range of topics, including: the definition of chronicity in wounds, the burden of illness, clinical outcomes of reducing healing time and the impact of early interventions on clinical and economic outcomes and the role of matrix metalloproteinases (MMPs) in wound healing. Method: A systematic review of the literature was carried out on the role of dressings in diabetic foot ulcer (DFU), and venous leg ulcer (VLU) management strategies, their effectiveness, associated resource use/cost, and quality of life (QoL) impact on patients. From this evidence-base statements were written regarding chronicity in wounds, burden of illness, healing time, and the role of MMPs, early interventions and dressings. A modified Delphi methodology involving two iterations of email questionnaires followed by a face-to-face meeting was used to validate the statements, in order to arrive at a consensus for each. Clinical experts were selected, representing nurses, surgeons, podiatrists, academics, and policy experts. Results: In the first round, 38/47 statements reached or exceeded the consensus threshold of 80% and none were rejected. According to the protocol, any statement not confirmed or rejected had to be modified using the comments from participants and resubmitted. In the second round, 5/9 remaining statements were confirmed and none rejected, leaving 4 to discuss at the meeting. All final statements were confirmed with at least 80% consensus. Conclusion: This modified Delphi panel sought to gain clarity from clinical experts surrounding the use of dressings in the management of chronic wounds. A full consensus statement was developed to help clinicians and policy makers improve the management of patients with these conditions

Formation and stabilisation of single current filaments in planar dielectric barrier discharge

In the experimental part we report on a typical bifurcation scenario of the current distribution in the discharge plane of a planar dielectric barrier discharge system. Increasing the amplitude $\hat U$ of the sinusoidal driving voltage after breakdown a large number of dynamic solitary filaments is observed and the subsequent decrease of $\hat U$ results in a pronounced hysteresis with decreasing number of filaments. In this way isolated single stationary filaments can be generated. In the theoretical part the latter are modeled by a reaction-drift-diffusion equation that is solved in three dimensional space numerically without any fitting procedure. As a result we obtain well defined stationary filaments of which size an shape essentially are independent of the initial conditions and having a width and an amplitude that agree with experiment rather well. On the basis of the numerical results we consider mechanisms of filament stabilisation. This includes the discussion of the well known surface charges as well as an additional focusing effect of volume charges

Transition from bright to dark dissipative solitons in dielectric barrier gas-discharge

In this article we deal with the experimental investigation of pattern formation in a planar ac gas-discharge system with a dielectric barrier. We report on the first observation of the transition from bright to dark current filaments and vice versa via stripe-like patterns. The observed phenomena become classified in the framework of Turing-structures and solitary objects and are compared to results obtained by numerical simulations of a two-component reaction-diffusion-system