Helicon Mode Formation and Radio Frequency Power Deposition in a Helicon Produced Plasma

Time- and space-resolved magnetic (B-dot) probe measurements in combination with measurements of the plasma parameters were carried out to investigate the relationship between the formation and propagation of helicon modes and the radio frequency (rf) power deposition in the core of a helicon plasma. The Poynting flux and the absorbed power density are deduced from the measured rf magnetic field distribution in amplitude and phase. Special attention is devoted to the helicon absorption under linear and nonlinear conditions. The present investigations are attached to recent observations in which the nonlinear nature of the helicon wave absorption has been demonstrated by showing that the strong absorption of helicon waves is correlated with parametric excitation of electrostatic fluctuations.

Space and phase resolved optical emission in mode transitions of radio-frequency inductively coupled plasmas

Inductively coupled radio-frequency plasmas can be operated in two distinct modes. At low power and comparatively low plasma densities the plasma is sustained in capacitive mode (E-mode). As the plasma density increases a transition to inductive mode (H-mode) is observed. This transition region is of particular interest and governed by non-linear dynamics, which under certain conditions results in structure formation with strong spatial gradients in light emission. These modes show pronounced differences is various measureable quantities e.g. electron densities, electron energy distribution functions, ion energy distribution functions, dynamics of optical light emission. Here the transition from E- to H- mode in an oxygen containing inductively coupled plasma (ICP) is investigated using space and phase resolved optical emission spectroscopy (PROES). The emission, measured phase resolved, allows investigation of the electron dynamics within the rf cycle, important for understanding the power coupling and ionization mechanisms in the discharge. The temporal variation of the emission reflects the dynamics of relatively high-energy electrons. It is possible to distinguish between E- and H-mode from the intensity and temporal behaviour of the emission.

Between “the Housewife” and “the Philosophy Professor”: Music, Narration and Address in Ousmane Sembene's Xala

The acclaimed Senegalese filmmaker Ousmane Sembene conceptualised himself as a modern day griot (West African oral performer), producing often didactic films that address a diverse spectatorship. Examining Xala, this paper argues that this address cannot be fully understood without attention to the film’s complex music/image relationships, which refigure classical and modernist film aesthetics to mobilise a discourse that recalls oral performance. In this way, Sembene negotiates the tensions of address generated by a spectatorship that is situated in the culturally hybrid spaces between the literate and the oral, the urban and the rural, and the global and the local.

Measurements, modeling and simulation of the off-body radio channel for the implementation of bodyworn antenna diversity at 868 MHz

This paper presents a systematic measurement campaign of diversity reception techniques for use in multiple-antenna wearable systems operating at 868 MHz. The experiments were performed using six time-synchronized bodyworn receivers and considered mobile off-body communications in an anechoic chamber, open office area and a hallway. The cross-correlation coefficient between the signal fading measured by bodyworn receivers was dependent upon the local environment and typically below 0.7. All received signal envelopes were combined in post-processing to study the potential benefits of implementing receiver diversity based upon selection combination, equal-gain and maximal-ratio combining. It is shown that, in an open office area, the 5.7 dB diversity gain obtained using a dual-branch bodyworn maximal-ratio diversity system may be further improved to 11.1 dB if a six-branch system was used. First-and second-order theoretical equations for diversity reception techniques operating in Nakagami fading conditions were used to model the postdetection combined envelopes. Maximum likelihood estimates of the Nakagami-parameter suggest that the fading conditions encountered in this study were generally less severe than Rayleigh. The paper also describes an algorithm that may be used to simulate the measured output of an M-branch diversity combiner operating in independent and identically-distributed Nakagami fading environments.

The challenge of revealing and tailoring the dynamics of radio-frequency plasmas

The complex dynamics of ionization and excitation mechanisms in capacitively coupled radio-frequency plasmas is discussed for single- and dual-frequency operations in low-pressure and atmospheric pressure plasmas. Electrons are energized through the dynamics of electric fields in the vicinity of the plasma boundary sheaths. Distinctly different power dissipation mechanisms can either co-exist or initiate mode transitions exhibiting characteristic spatio-temporal ionization structures. Phase resolved optical emission spectroscopy, in combination with adequate modelling of the population dynamics of excited states, and numerical simulations reveal dissipation associated with sheath expansion, sheath collapse, transient electron avalanches and wave–particle interactions. In dual-frequency systems the relative phase between the two frequency components provides additional strategies to tailor the plasma dynamics.

"Thought-Tormented Music": Joyce and the Music of the Irish Revival

"In this special issue's opening essay, Martin Dowling devotes almost half of "'Thought-Tormented Music': Joyce and the Music of the Irish Revival" to what he calls "the situation of music in the Irish literary revival." He focuses chiefly on 1904, which was both an intensely productive period for the revival movement and a year chock-full of crucial events and decisions for Joyce. Drawing on the works of Pierre Bourdieu and Jaques Lacan, Dowling explores the revivalists' efforts to "de-anglicize" Irish music, to remove foreign influences that distorted the "pure tradition of Irish song," and to achieve an improbable harmony between the music favoured by the disappearing Anglo-Irish aristocracy and the Irish-speaking peasantry. Inevitably, disputes occurred over what constituted "authentic" Irish music. Factions quarrelled over whether pristine Irish music existed in the Atlantic seaboard or more inland; whether "authentic" songs were sung with or without instrumental accompaniment; and whether the piano, rather than the traditional harp, was a legitimate instrument of accompaniment. Having delineated the historical and theoretical context, Dowling offers a richly detailed analysis of Joyce's story "A Mother." He reveals how almost every element in the story--from the Eire Abu Society to the Antient Concert Rooms, from the conflict between Mrs. Kearney and Hoppy Holohan to the plight of Kathleen Kearney--is charged with meaning by the subtextual conflicts of the revivalists' agenda. Dowling explains also the "authenticity" in Joyce's depiction of vocal performances of "The Lass of Aughrim" in "The Dead" and "The Croppy Boy" in "Sirens," which he calls two "true gems" of authentic Irish music." --Introduction by Charles Rossman and Alan W. Friedman, Guest Editors, pp. 409-410

Spatial Perception and Cognition in Multichannel Audio for Electroacoustic Music

Listeners experience electroacoustic music as full of significance and meaning, and they experience spatiality as one of the factors contributing to its meaningfulness. If we want to understand spatiality in electroacoustic music, we must understand how the listener’s mental processes give rise to the experience of meaning. In electroacoustic music as in everyday life, these mental processes unite the peripheral auditory system with human spatial cognition. In the discussion that follows we consider a range of the listener’s mental processes relating space and meaning from the perceptual attributes of spatial imagery to the spatial reference frames for places and navigation. When considering multichannel loudspeaker systems in particular, an important part of the discussion is focused on the distinctive and idiomatic ways in which this particular mode of sound production contributes to and situates meaning. These idiosyncrasies include the phenomenon of image dispersion, the important consequences of the precedence effect and the influence of source characteristics on spatial imagery. These are discussed in close relation to the practicalities of artistic practice and to the potential for artistic meaning experienced by the listener.

Meaning in Electroacoustic Music and the Everyday Mind

The key question posed here is how listeners experience meaning when listening to electroacoustic music, especially how they experience it as art. This question is addressed by connecting electroacoustic listening with the ways that the mind constructs meaning in everyday life. Initially, the topic of the everyday mind provides a framework for discussing cognitive schemas, mental spaces, the Event schema and auditory gist. Then, specific idioms of electroacoustic music are examined that give rise to artistic meaning. These include the creative binding of circumstances with events and the conceptual blending that creates metaphorical meaning. Finally, the listener's experience of long-term events is discussed is relation to the location event-structure metaphor.

Juxtaposition and Non-Motion: Varese Bridges Modernism and Electroacoustic Music

Edgard Vare` se’s Poe` me e´ lectronique can be viewed as a bridge between early twentieth-century modernism and electroacoustic music. This connection to early modernism is most clearly seen in its use of musical juxtaposition, a favoured technique of early modernist composers, especially those active in Paris. Juxtaposition and non-motion are considered here, particularly in relationship to Smalley’s exposition of spectromorphology (Smalley 1986), which in its preoccupation with motion omits any significant consideration of non-motion. Juxtaposition and non-motion have an important history within twentieth-century music, and as an early classic of electroacoustic music, Poe` me e´ lectronique is a particularly striking example of a composition that is rich in juxtapositions similar to those found in passages of early modernist music. Examining Poe` me e´ lectronique through the lens of juxtaposition and non-motion reveals how the organisation of its juxtaposed sounds encourages the experience of sound structure suspended time.