Sound scattering by marine organisms was studied off the Oregon coast and between Hawaii and Adak, Alaska. Variations in scattering were observed over a period of several hours, over did (24-hour) periods, from month to month, from inshore to offshore, in relation to biomass of midwater animals, and temperature and salinity. Usually one or two scattering layers migrated vertically, ascending or descending at dusk and dawn respectively. At times reflectors migrated between surface waters and upper scattering layers during twilight periods. No statistical difference was found between rates of ascent and descent because of the variability in rates of migration that was observed. The amount or thickness of scattering in the water column was found to vary from day to night and with seasons. There was a general trend for more scattering during night than day, yet it was not statistically significant. Seasonally, more scattering appeared to be present during the summer in some years but not in others. Surface scattering varied not in amount but in the type present during different seasons and between day and night. Geographically, scattering was found in smaller amounts in offshore than inshore waters of Oregon. Variations in scattering were noted among the water masses between Hawaii and Adak, Alaska. Geographic changes in scattering and biomass showed a positive correlation between euphausiid catches and the amount of scattering. However, euphausiids are not considered the only group scattering sound. The great amount of variability in scattering is discussed. It may be due to differences in the species causing scattering and variability in the behavior of individual species, possibly resulting from changes in light and temperature. / Graduation date: 1968

In this study, bottom mounted ADCP and RCM 9 were deployed to collect time series data of current, turbidity and acoustic backscattered echo intensity (EI) in the estuarine environment near Love River and in the coastal waters of Howan. Our results indicate that in the torrential rain event, the Love River became very turbid with the flow speed exceeding 1.5 m/s. ADCP EI data also increase rapidly and correlate well with the turbidity data. Based on the empirical formula of Kim and Voulgaris (2003), the EI time series data of the first bin are converted into sediment suspension concentration (SSC), which compared reasonably well with those converted from the optical observations of turbidity. Therefore, ADCP EI data can be used as a good proxy of SSC. Velocity profiles measured by ADCP were also analyzed to obtain the friction velocity and roughness length according to the logarithmic relationship. The log layer height extended to almost full channel depth of 4 m during strong flows, the roughness lengths were about 10-3 m and the bottom shear stress reached 10 Pa. It is not surprising that bottom sediments are stirred under such a large shear stress. The sediment suspension due to current and wave action in the rather clear coastal waters of Howan is also investigated by means of ADCP EI data. In winters the observed current speed is stronger while the wave height is smaller (Hs<1 m). It is found that the near-bottom ADCP EI data have better correlation with the current magnitude but poorer correlation with surface waves. On the other hand, the ADCP EI data near the sea surface become more dependent on the surface waves. This is possible due to the bubbles entrained by breaking waves, especially under the condition of Hs>0.5 m. In summers the observed current speed is weaker while the wave height is generally higher. In one typhoon event the observed Hs even reached 4.5 m. The calculated maximum orbital velocity at the bottom and bed shear stress generated by surface waves are sufficient to mobilize sediment. The ADCP EI data of the whole water column (about 15 m) correlate nicely with the wave height but correlate poorly with current magnitude. In contrast to the results of the Love River, the near-bottom ADCP EI data show a weak correlation with the turbidity observation.

This thesis contributes to knowledge by describing two novel methods to calculate 3D blood velocity and flow within the heart using 3D colour Doppler images. The principal goal of both methods was to overcome the main limitation of Doppler systems which is that the Doppler effect only measures one component of the velocity (parallel to the beam direction). For that reason, measured velocity and calculated flow depend on the angle between the beam direction and the flow. The first method was developed to reconstruct 3D intracardiac velocity vector fields. This is the first time that such vector fields have been obtained from 3D colour Doppler images. The novelty of the proposal lies not only in the 3D velocity reconstruction, but also 1) a new noise model for colour Doppler images was proposed which improves the realism of simulation studies, 2) an efficient patch-wise implementation was introduced and 3) ventricle wall motion was used to enable full ventricular coverage. Based on simulations minimum acquisition requirements for accurate reconstruction were established. These requirements were: view angles over 20 degrees and noise below 10% of the Doppler maximum velocity. The method was tested on healthy volunteers and on paediatric patients and an accuracy of 15% compared to flow Magnetic Resonance Imaging (MRI) was obtained, when acquisition and data conditions were close to the optimum range. The second method proposes an algorithm to calculate angle-independent flow rates through surfaces within the heart and vessels. Built on the Gauss’s theorem, this method enables to increase coverage beyond the Field of View (FoV) of individual colour Doppler images by combining images acquired from multiple views. The method was validated in patients with Hypoplastic Left Heart Syndrome. Results were compared with the current clinical gold standard measurement of flow MRI, agreeing on flow values and volumes to less than 10%. The novel methods proposed in this thesis have shown encouraging results using volunteer and patient data. I hope that the methods proposed will in the future be able to offer advanced flow measurements using echo. The ability to improve the information available from echo imaging, due to its ease of use and cost effective nature, has the potential for widespread improvements in clinical care.

No description available.

No description available.

No description available.

In recent years, high speed data communications over twisted pair cables has gained tremendous demand. Asymmetric Digital Subscriber Line (ADSL) was standardized for use over twisted pair cables. A critical component in ADSL system is the echo canceller which is intended to discriminate unwanted echo signals caused by twisted pair interface circuit called the hybrid. An echo signal is characterized by the hybrid and the line type the hybrid is connected to. Recently, there has been a great concern that the echo signal displays wide variations when the twisted pair cable is shared with a telephone. The amount of echo signal present in the receiver will directly influence the ADSL system performance. Hence, high performance echo canceller with good tracking capability is required. In this thesis, a new adaptation scheme called Modified Conjugate Gradient method is proposed and applied to ADSL echo canceller. It is shown that superior tracking capability is obtained compared to previously proposed echo canceller using Least Mean Square (LMS) method while compromising small amount of computational complexity. / Graduation date: 1999

Thesis (Ph.D.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 76-82)

Thesis (M.S.)--University of Wisconsin--Madison. / Typescript. Includes bibliographical references (leaves 77-78).

Thesis (M. Eng.)--Carleton University, 1992. / Also available in electronic format on the Internet.