Relative Auditory Distance Discrimination With Virtual Nearby Sound Sources

In this paper a psychophysical experiment targeted at exploring relative distance discrimination thresholds with binaurally rendered virtual sound sources in the near field is described. Pairs of virtual sources are spatialized around 6 different spatial locations (2 directions 7 3 reference distances) through a set of generic far-field Head-Related Transfer Functions (HRTFs) coupled with a near-field correction model proposed in the literature, known as DVF (Distance Variation Function). Individual discrimination thresholds for each spatial location and for each of the two orders of presentation of stimuli (approaching or receding) are calculated on 20 subjects through an adaptive procedure. Results show that thresholds are higher than those reported in the literature for real sound sources, and that approaching and receding stimuli behave differently. In particular, when the virtual source is close (< 25 cm) thresholds for the approaching condition are significantly lower compared to thresholds for the receding condition, while the opposite behaviour appears for greater distances (~ 1 m). We hypothesize such an asymmetric bias to be due to variations in the absolute stimulus level

Measurement of head-related transfer functions : A review

A head-related transfer function (HRTF) describes an acoustic transfer function between a point sound source in the free-field and a defined position in the listener's ear canal, and plays an essential role in creating immersive virtual acoustic environments (VAEs) reproduced over headphones or loudspeakers. HRTFs are highly individual, and depend on directions and distances (near-field HRTFs). However, the measurement of high-density HRTF datasets is usually time-consuming, especially for human subjects. Over the years, various novel measurement setups and methods have been proposed for the fast acquisition of individual HRTFs while maintaining high measurement accuracy. This review paper provides an overview of various HRTF measurement systems and some insights into trends in individual HRTF measurements

Development of High-Speed Laser Diagnostics for the Investigation of Scalar Heterogeneities.

The development of advanced engine concepts are, to a large extent, hindered by the lack of suitable multidimensional optical diagnostics that can measure heterogeneities in engines. The combustion process is a complex function of species concentration, temperature, pressure, and flow fields. Fine-tuning the combustion process for efficient combustion with low emissions therefore requires detailed knowledge of these parameters as they vary with space and time. Novel optical diagnostic techniques which probe relevant quantities can either be used to address a specific problem, as with misfires and partial burns in a spark ignition direct-injection (SIDI) stratified charge (SC) gasoline engines; to develop models, such as boundary layer temperature field measurements; or serve both purposes. For these two examples, there are currently no diagnostics which meet the needs of engine developers and modelers, which motivated the current work. Investigations of misfires and partial burns can benefit from novel and improved fuel concentration and combustion progress diagnostics. A high-speed, planar, quantitative fuel concentration diagnostic technique based on laser-induced fluorescence (LIF) of biacetyl was utilized in unison with a spark plug absorption probe to aid in the understanding of both approaches. The LIF diagnostic was improved by using a dual laser approach which increased the signal to noise ratio. Also, its ability to track flame fronts and observe outgassing from engine crevices was demonstrated. The suitability of xxii the spark plug absorption probe for use in an SIDI SG engine was demonstrated. Next, a simplified combustion progress diagnostic using LIF of hydroxyl radicals was demonstrated, which avoids the cost and complexity associated with conventional approaches. Lastly, a novel, high speed, high resolution LIF diagnostic called two color toluene thermometry was developed to quantitatively measure boundary layer temperature fields. Calibration measurements were performed in a heated jet. The diagnostics were then adapted from a two camera design to a single camera design for simplicity and used to evaluate temperature gradients in an engine boundary layer. The results provided insight into the structure of the boundary layer during different parts of the engine cycle and for different engine operation conditions.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91418/1/mcundy_1.pd

The physics of streamer discharge phenomena

In this review we describe a transient type of gas discharge which is commonly called a streamer discharge, as well as a few related phenomena in pulsed discharges. Streamers are propagating ionization fronts with self-organized field enhancement at their tips that can appear in gases at (or close to) atmospheric pressure. They are the precursors of other discharges like sparks and lightning, but they also occur in for example corona reactors or plasma jets which are used for a variety of plasma chemical purposes. When enough space is available, streamers can also form at much lower pressures, like in the case of sprite discharges high up in the atmosphere. We explain the structure and basic underlying physics of streamer discharges, and how they scale with gas density. We discuss the chemistry and applications of streamers, and describe their two main stages in detail: inception and propagation. We also look at some other topics, like interaction with flow and heat, related pulsed discharges, and electron runaway and high energy radiation. Finally, we discuss streamer simulations and diagnostics in quite some detail. This review is written with two purposes in mind: First, we describe recent results on the physics of streamer discharges, with a focus on the work performed in our groups. We also describe recent developments in diagnostics and simulations of streamers. Second, we provide background information on the above-mentioned aspects of streamers. This review can therefore be used as a tutorial by researchers starting to work in the field of streamer physics.Comment: 89 pages, 29 figure

Root Causes of Cycle-to-Cycle Combustion Variations in Spark Ignited Engines.

Stricter governmental emission regulations, climate change concerns, and consumer demands for high fuel efficiency push the development of advanced cleaner and more efficient combustion strategies. Many strategies that rely on spark ignition are limited in their peak efficiencies by excessive cycle-to-cycle combustion variations (CCV). In this study, various laser-based and passive optical techniques are used to measure flow fields, spark discharge and other factors that impact early flame growth from which CCV originate. Bulk flow motion, as one contributing factor to CCV, is characterized in an optical engine under motored and fired conditions. In the fired cases, the flow velocities are higher during the gas exchange period but lower at the time of ignition, due to higher charge viscosities, caused by higher gas temperatures. Ten different fuel-air mixtures are strategically chosen to isolate the effects of laminar flame speed, thermo-diffusive mixture properties and change of stoichiometrically deficient species on the mechanisms that are responsible for cycle-to-cycle variability. Single value decomposition methods are found to be inefficient in identifying flow structures that are related to combustion variability. Physical flow parameters such as velocity magnitude and shear strength around time of ignition are identified to affect combustion variability. The relative impact of these parameters on energy output and combustion phasing are quantified for all mixtures and show some weak dependence on Markstein number and laminar flame speed. In a more fundamental fan-stirred combustion vessel experiments, variability effects of flame-flow interactions on CCV are isolated and thermo-diffusive effects are shown to impact combustion variability. Unstable negative Markstein number mixtures tend to exhibit higher combustion variability when interacting with gradients in the flow field around the time of ignition. High shear strength at the point of ignition causes an increased flame wrinkling, increasing the surface area, leading to faster combustion. This is an important finding because the common Lewis number equals 1 assumption in CFD simulations might lead to an under-prediction of CCV in low turbulence cases for negative Markstein number mixtures.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/133396/1/pschiffm_1.pd

Dye laser traveling wave amplifier

Injection locking was applied to a cavity-dumped coaxial flashlamp pumped dye laser in an effort to obtain nanosecond duration pulses which have both high energy and narrow-linewidth. In the absence of an injected laser pulse, the cavity-dumped dye laser was capable of generating high energy (approx. 60mJ) nanosecond duration output pulses. These pulses, however, had a fixed center wavelength and were extremely broadband (approx. 6nm FWHM). Experimental investigations were performed to determine if the spectral properties of these outputs could be improved through the use of injection-locking techniques. A parametric study to determine the specific conditions under which the laser could be injection-locked was also carried out. Significant linewidth reduction to 0.0015nm) of the outputs was obtained through injection-locking but only at wavelengths near the peak lasing wavelength of the dye. It was found, however; that by inserting weakly dispersive tuning elements in the laser cavity, these narrow-linewidth outputs could be obtained over a wide (24nm) tuning range. Since the tuning elements had low insertion losses, the tunability of the output was obtained without sacrificing output pulse energy

Development of Particle Image Velocimetry for Plasma Induced Flow Measurements

There has been an increased interest in the use of flow control in aerodynamics and combustion to improve efficiency and reduce emissions. Plasma flow control is one way by using active flow control affect these desired changes. Spark plasma actuators have capabilities of inducing heat and momentum to the flow field. The flow field generated by this plasma induces complex pressure and temperature gradients that lead to the development of complex flow structures. The experiment described in this research is particularly difficult due to its small scale, and the dynamic range of velocities that are induced by the flow field. This flow field is yet to be quantified by previous research. The flow field generated by spark plasma has not been quantified to date. The development of a set-up to capture and process preliminary findings of the flow field generated by a spark plasma under quiescent conditions is imperative to understanding the capabilities of this plasma actuator

Spectroscopic Measurement of Gas Temperature in Small Internal Combustion Engines

The Small Engine Research Bench (SERB) was used previously to measure spatially and temporally averaged heat flux, as well as local, instantaneous heat flux at several external locations, for a series of small engines (1 - 10 kW). This investigation obtained time averaged crank angle resolved measurements of the in-cylinder gas temperature using Fourier transform infrared (FTIR) absorption thermometry. The results, coupled with heat flux measurements, will enable the validation or refinement of existing thermal energy loss models