Structural-acoustic coupling and psychophysical effects in the active control of noise in vehicles

Active noise control systems offer a potential method of reducing the weight of passive acoustic treatment and, therefore, increasing vehicles' fuel efficiency. These can be particularly cost-efficient if integrated with the entertainment system. A combined system is presented employing feedforward control of engine noise and feedback control of road noise, using a `modal' error signal. Due to the dependence of the feedback system on the modal response of the vehicle cabin, the influence of structural-acoustic coupling on this response and the consequent effects on the control performance are investigated. Simulations of the performance of the control systems in rigid and non-rigid enclosures show that the feedforward component is largely unaffected by structural-acoustic coupling, whilst the modal feedback performance is reduced by 3 dB due to the shift in the frequency of the targeted acoustic mode. The simulation results are confirmed through experiments conducted in a structural-acoustic coupled enclosure

Design and implementation of a personal audio system in a car cabin

The generation of personal listening zones in a car cabin would allow the different occupants to listen to different audio programmes without the use of headphones. This would allow, for example, the driver to listen to a navigation system whilst the rear passengers watched a film. Personal audio systems have previously been implemented in mobile devices and monitors, for example, however, the investigation of the effects of an enclosure on the generation of personal listening zones has been limited. This paper presents an investigation of the effects of a car cabin sized enclosure on the generation of independent listening zones in the front and rear seats. The standard car audio loudspeaker array is used to produce independent listening zones at low frequencies, while a second array of small loudspeakers positioned at the four headrest positions is used to provide control over the rest of the audio bandwidth. The proposed arrays are implemented in a real car and the results of a real-time implementation are presented.<br/

Multichannel control systems for the attenuation of interior road noise in vehicles

This paper considers the active control of road noise in vehicles, using either multichannel feedback control, with both headrest and floor positioned microphones providing feedback error signals, or multichannel feedforward control, in which reference signals are provided by the microphones on the vehicle floor and error signals are provided by the microphones mounted on the headrests. The formulation of these control problems is shown to be similar if the constraints of robust stability, limited disturbance enhancement and open-loop stability are imposed. A novel formulation is presented for disturbance enhancement in multichannel systems, which limits the maximum enhancement of each individual error signal. The performance of these two systems is predicted using plant responses and disturbance signals measured in a small city car. The reduction in the sum of the squared pressure signals at the four error microphones for both systems is found to be up to 8 dB at low frequencies and 3 dB on average, where the sound level is particularly high from 80 to 180 Hz. The performance of both systems is found to be robust to measured variations in the plant responses. The enhancements in the disturbance at higher frequencies are smaller for the feedback controller than for the feedforward controller, although the performance of the feedback controller is more significantly reduced by the introduction of additional delay in the plant response.<br/

Tourism and islandscapes: Cultural realignment, social-ecological resilience and change

If, as according to Robin (2015: online), "islands are idealised ecological worlds, the Edens of a fallen planet'", the rationale underpinning tourism expansion should acknowledge MacLeod's (2013) notion of "cultural realignment" that calls for optimal and resilient encounters. This introductory article to the subsequent theme section of the journal on sustainable tourism acts as a bridge toward the development of emergent themes that describe how island peoples adapt and respond in localised cultural islandscapes as a consequence of tourism expansion. The links between cultural alignment and social-ecological resilience are clear and the principal and overarching question posed in this introductory article is: To what extent are islandscapes resilient to rapidly changing utilities, significances and ways of life wrought by tourism expansion? The vulnerabilityresilience duality remains firmly entrenched in the discourse on islands where tourism has become prominent, and although tourism provides some resiliency, overall, islandscapes remain subject to externally driven fast and slow change that exercises an overwhelming influence. Islander agency will likely remain subject to the fluctuations in the demands of the tourism supply chain. Therefore, tourism as a standalone focus of islands is a high-risk proposition, especially in contexts where externally driven change is likely to intensify

Travelling waves in a tissue interaction model for skin pattern formation

Tissue interaction plays a major role in many morphogenetic processes, particularly those associated with skin organ primordia. We examine travelling wave solutions in a tissue interaction model for skin pattern formation which is firmly based on the known biology. From a phase space analysis we conjecture the existence of travelling waves with specific wave speeds. Subsequently, analytical approximations to the wave profiles are derived using perturbation methods. We then show numerically that such travelling wave solutions do exist and that they are in good agreement with our analytical results. Finally, the biological implications of our analysis are discussed

Dynamic changes in accumbens dopamine correlate with learning during intracranial self-stimulation

Dopamine in the nucleus accumbens (NAc) is an important neurotransmitter for reward-seeking behaviors such as intracranial self-stimulation (ICSS), although its precise role remains unclear. Here, dynamic fluctuations in extracellular dopamine were measured during ICSS in the rat NAc shell with fast-scan cyclic voltammetry at carbon-fiber microelectrodes. Rats were trained to press a lever to deliver electrical stimulation to the substantia nigra (SNc)/ventral tegmental area (VTA) after the random onset of a cue that predicted reward availability. Latency to respond after cue onset significantly declined across trials, indicative of learning. Dopamine release was evoked by the stimulation but also developed across trials in a time-locked fashion to the cue. Once established, the cue-evoked dopamine transients continued to grow in amplitude, although they were variable from trial to trial. The emergence of cue-evoked dopamine correlated with a decline in electrically evoked dopamine release. Extinction of ICSS resulted in a significant decline in goal-directed behavior coupled to a significant decrease in cue-evoked phasic dopamine across trials. Subsequent reinstatement of ICSS was correlated with a return to preextinction transient amplitudes in response to the cue and reestablishment of ICSS behavior. The results show the dynamic nature of chemical signaling in the NAc during ICSS and provide new insight into the role of NAc dopamine in reward-related behaviors