Christopher Clark

Production and perception of sibilant fricatives: Shona data

This research began out of two overlapping motives. First, we have been observing what have impressionistically been termed ‘whistling’ fricatives in Shona (and also, though not reported here, in another language, Jibbali); we felt that there was room for a fuller analysis of some aspects of their production characteristics. Second, sibilance in general offers plenty of scope for what Delattre called the ‘quest of the Holy Grail’ in phonetics: the search for features of relevance to perception. More background to both the production and the perception issues will be given as we proceed.

The Politics of Conversion: Missionary Protestantism and the Jews in Prussia, 1728-1941

Missionaries are people who operate on the border between their own community and another. The confessional frontier between the Christian and the Jewish communities in Prussia offers a privileged vantage-point from which to analyze the relationship between them. This study makes comprehensive use of the archives and publications of the various Prussian institutions and societies which set out to convert Jews to Christianity. Spanning over two centuries of Protestant missionary activity, this book examines the ways in which theological, social, and racial themes intertwined in the relationship between the Christian majority in Prussia and the Jewish minority in its midst. This study sheds light on a facet of Jewish-German history which has been overshadowed by the ultimate tragedy of the Holocaust.

Application of a blind source separation algorithm for the detection and tracking of tornado-generated infrasound emissions during the severe weather outbreak of 27 April 2011

April 25-28, 2011 has been identified by many as the most significant and severe single-system outbreak of tornadoes in recorded history. One day in particular, the 27th of April, has been classified by the National Oceanic and Atmospheric Administration (NOAA) as the fourth deadliest tornado outbreak in US history. Severe tornadic activity on this day levied catastrophic damage to life and property across areas of Mississippi, Alabama, Georgia and Tennessee. During this outbreak, multiple Ducommun Miltec-developed infrasound sensors collecting continuous, high resolution data were deployed in two-dimensional array configurations in Northern Alabama. Prior research on the collection and analysis of infrasonic emissions from severe weather phenomenon has provided much insight on the nature of tornado-generated infrasound. Our effort focuses on the application of novel bearing estimation algorithms using closely spaced (4-6 m) array elements. Direction of Arrival (DOA) estimates, derived from Blind Source Separation (BSS) techniques, will be presented for at least two significant tornadoes: the long-track EF5 that impacted Hackleburg and Phil Campbell, AL and the large multi-vortex EF4 that struck Cullman, AL. Correlation of infrasound detection and bearing estimate initiation and termination with NOAA Storm Prediction Center (SPC) Storm Reports will also be reviewed.

Passive acoustic monitoring on the North Atlantic right whale calving grounds

Shallow water environments, such as the North Atlantic right whale calving grounds, pose a challenge to cetacean passive acoustic monitoring due to high variability in ambient noise and environmental conditions. In this region of high shipping traffic and increased ship-strike risk, passive acoustic monitoring may reduce right whale ship strikes. This study describes temporal variability in right whale call detections, ambient noise sources, and environmental conditions on the right whale calving grounds during 2009-2010 and 2010-2011. Right whale detections occurred between November 19 and March 11, on up to 25% of days per deployment with increased nocturnal call detections, and increased acoustic presence off Jacksonville, FL during 2010-2011. Shipping noise was most common off Jacksonville, detected in up to 74% of minutes, with a diurnal peak, while tidally-associated broadband impulses were detected in up to 43% of minutes off Savannah GA. Environmental conditions including SST, wind, waves, and tid...

Detection of FM signals in the presence of non‐Gaussian noise

In bioacoustics, the problem of detecting frequency‐modulated signals in the presence of non‐Gaussian noise is of great interest. Matched filters (MF) are often chosen over frequency‐specific energy (FSE) detectors because of their improvement in both signal gain and target specificity. Under non‐Gaussian conditions however, MF detectors do not ensure acceptable trade‐off between false alarm and missed detection rate. To decrease false alarm rate, we propose a two‐stage detection technique. First, a MF is applied, with threshold prescribed by the acceptable false alarm rate, to generate candidate detections. Second, a signal recognition (SR) algorithm is applied to the candidates. The SR algorithm estimates modulation parameters from the signal spectrogram, and a detection decision is made based on how well parameters match a criterion set for the signal of interest. We applied this technique to right whale contact calls recorded in Cape Cod Bay. Results demonstrate that the MF‐SR technique decreases fals...

Vocalizations of blue whales in the Antarctic: Implications for the use of passive acoustics for population studies on baleen whales

Stereotypical calls of baleen whales can be a diagnostic field characteristic for determining species and stocks. Repeated series of these calls may be used for long‐term population studies using passive acoustics. Vocalizations were recorded from 15 groups of blue whales (consisting of 42 individuals) during the 2001–02 and 2002–03 International Whaling Commission‐Southern Ocean Whale and Ecosystem Research (IWC‐SOWER) surveys in Antarctic waters north and east of the Ross Sea. Long‐duration vocalizations attributed to Antarctic blue whales included 28‐Hz ‘‘tones,’’ 28 Hz ‘‘downsweeps,’’ and the more complex ‘‘3‐unit’’ calls (considered to be song units). The 28‐Hz component was stable for all three calls, regardless of signal strength. The 3‐unit calls varied in their 2nd and 3rd units and were heard in only 10 out of the 15 groups. There was no evidence of repeated patterns (song phrases) of 3‐unit calls. The results of this study suggest that the 28‐Hz peak frequency may be used as a diagnostic featur...

High resolution beamforming for small aperture arrays

Achieving fine resolution bearing estimates for multiple sources using acoustic arrays with small apertures, in number of wavelengths, is a difficult challenge. It requires both large signal‐to‐noise ratio (SNR) gains and very narrow beam responses. High resolution beamforming for small aperture arrays is accomplished by exploiting acoustical fluctuations. Acoustical fluctuations in the atmosphere are caused by wind turbulence along the propagation path, air turbulence at the sensor, source/receiver motion, unsteady source level, and fine scale temperature variations. Similar environmental and source dependent phenomena cause fluctuations in other propagation media, e.g., undersea, optics, infrared. Amplitude fluctuations are exploited to deconvolve the beam response functions from the beamformed data of small arrays to achieve high spatial resolution, i.e., fine bearing resolution, and substantial SNR gain. Results are presented for a six microphone low‐frequency array with an aperture of less than three...

Performance of conventional and fluctuation‐based signal detection applied to atmospheric acoustics in the presence of transients

One problem encountered in atmospherics acoustics is the detection of steady signals in the presence of loud transient noise. The ability to discriminate against loud transients is an attractive feature of fluctuation‐based beamforming. A fluctuation‐based beamformer was developed and there was a need to evaluate its performance for acoustic environments that have frequently occurring transients. Synthetic noise fields, which included loud transient noise, were created. Subsequently, receiver operating characteristic (ROC) curves could be produced in a Monte Carlo fashion. In order to provide a benchmark, the results of a conventional beamformer were similarly tested via ROC curves. These ROC curves allowed for comparison of the two beamformers under specific signal and noise conditions. In this presentation, the effects of transients on the outputs of both the conventional beamformer and the fluctuation‐based beamformer are discussed. Particular interest is focused on the amplitude distribution of the ou...

Why do whales communicate at the frequencies they do? Lessons from underwater acoustic signal processing

The combination of frequency‐dependent attenuation of acoustic energy and the ambient noise field of the deep ocean provides a window of opportunity for acoustic communication ranging from 10 to 1000 Hz. Why do pelagic whale species choose to use center frequencies between 20 and 50 Hz rather than higher frequencies in the window of opportunity? It is not a size limitation, because similar size whales which reside nearby in shallow water have center frequencies of propagation from 400 to 700 Hz. Experience in underwater signal processing has shown that internal wave scattering can be significant for acoustic frequencies above 50 Hz. Here the postulate is presented that deep‐water whales (blues and fins) have chosen to send acoustical signals at 20 Hz to minimize internal wave scattering of their acoustic energy. The implications to range of detection will be made from a signal processing point of view and the impact that this would have on marine mammal biology will also be presented. Similar arguments, t...

Auschwitz and Hiroshima

Explaining Auschwitz and Hiroshima: History Writing and the Second World War, 1945–1990. By R. J. B. Bosworth (London and New York: Routledge, 1993) xv + 260 pps. £40.00 cloth.