52 research outputs found

    Dielectric-barrier discharges in two-dimensional lattice potentials

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    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

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

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    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 (α\alpha process), secondary electron emission from the cathode (γ\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 γ\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

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    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

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    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

    Physical aspects of the crystalline electric field (CEF)

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    The present article describes some important effects that the crystalline electric field (CEF) produces in solids and particularly in metals. Emphasis is laid on a description in simple physical terms rather than on detailed mathematical analysis. We first give an outline of the way the CEF acts as a perturbation on the spectroscopic state of the free ion and we discuss briefly the limits of the model including its relation to chemical binding. We then describe the consequences of the CEF interaction including the information that may be obtained from experiment. We discuss the following topics: magnetic moment, susceptibility, magnetic anisotropy, Schottky specific heat, electron paramagnetic resonance, hypertine structure, magnetic form factor, neutron scattering from CEF levels, magnetic excitons and light scattering. In particular we emphasize the relation between CEF effects and neutron scattering because the availability of strong thermal neutron sources will certainly stimulate this field of research

    Drift bifurcation of dissipative solitons in barrier gas discharge

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    In an ac-driven planar barrier gas-discharge system we observe solitary structures in the luminescence radiation density and the related current distribution that exhibit rather irregular motion. Using a stochastic data analysis, it can be demonstrated that two types of trajectories can be found: the first type originates from a uniform motion which is superimposed with noise, whereas the latter type is purely noise driven. The bifurcation between the two types of motion can be observed when changing the external driving voltage

    Rotational bifurcation of localized dissipative structures

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    A topic of great interest for pattern-forming systems is the possibility of a spontaneous change in symmetry and dynamics as one slowly varies an external parameter. In this letter, we identify that a stationary localized structure without rotational symmetry, such as a pair of bound dissipative solitons, can spontaneously begin to rotate. The underlying mechanism is similar to the widely studied mechanism of the drift bifurcation in which structures begin to drift at constant velocity. We find a particular example of this new bifurcation for a 3-component reaction-diffusion system in 2 dimensions, and show that it can precede the drift bifurcation
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