Ring piezoelectric transducers radiating ultrasonic energy into the air

Ring piezoelectric transducers generating ultrasonic energy in air were designed and tested experimentally and numerically. The radiation pattern of the transducer is very narrow (4 degrees ) and its frequency response has a broadband character. Resonant frequencies of the transducers were determined experimentally and verified theoretically. Applications of the proposed ring transducers in a robotic ranging system were examined.     

Translational motion compensation for coronary angiogram sequences

A method of compensating for the lag of the video cameras typically used in angiographic systems is presented for use in sequences of digitized X-ray images. The lag effect is reduced by a straightforward weighted subtraction, which has the undesirable side effect of increasing noise. By superimposing several lag-corrected and appropriately shifted images, however, the signal-to-noise ratio can be restored. The algorithm uses the phase-correlation method to measure the two-dimensional shift of a mobile coronary arterial structure. Processing is confined to a rectangular area of interest (AOI), which encloses a feature of clinical significance. The differences of the phases of the Fourier transforms of two frames is computed, combined with an appropriate filter, and inverse Fourier-transformed to produce a phase-correlation image. The vector separation from the origin of image space of the peak of the phase-correlation image is the estimate of the shift of the artery's position in the second frame as compared to the first. The isolation of the AOI from the surrounding image is achieved by the application of a window and correction for any linear trend in the background intensity.     

Injection locking techniques for a 1-GHz digital receiver using acoustic-wave devices

The use of surface-transverse-wave (STW) resonator-based oscillators as amplifiers and as carrier recovery elements is discussed. It is demonstrated that these oscillators can amplify phase-shift-keyed signals with very little added noise, while providing a constant output power. Their performance in carrier recovery amplifications is analyzed. Experimental results showing the amplification with more than 80 dB of dynamic range of a 2 Mb/s BPSK signal and the carrier recovery of an 8 Mb/s signal with a 1-GHz STW oscillator are shown.     

Aspects of modeling the frequency response of a two-port waveguide-coupled SAW resonator-filter

Coupling-of-modes-in-time and coupling-of-modes-in-space analyses are applied to the modeling of a two-port two-pole waveguide-coupled SAW resonator filter. Modeling is applied to a lumped equivalent circuit and a distributed circuit. While the accuracy of the coupling estimation dictates the exact mode-splitting and bandwidth, the ensuing computations can give a good representation of the amplitude and phase response, including the effect of degenerate transverse modes.     

Quantitative ECT: Comparison of Recovery Coefficient and Linearity of Detector Response for Single Photon and Coincidence Detection (F-18, B+ 511 keV)

The response characteristics of two tomographic systems were compared for imaging of positron emitters: a) a SPECT system with a 3/8 in crystal and 511 keV detector shielding, equipped with a specially designed 511 keV collimator, and b) a PET V system using coincidence detection. SPECT transverse plane resolution was 19 mm FWHM and 35 mm FWTM for a radius of rotation of 16 cm. Corresponding resolution for PET was 14 mm FWHM and 28 mm FWTM. Transverse images through a phantom containing cylindrical sources of various cross sections and uniform activity were obtained for each detector. The measured count density or recovery coefficient was found to decrease with source size, the dependence being similar for both systems. The theoretical values for recovery coefficients were calculated by convolution of a Gaussian fit to the SPECT resolution (FWHM, FWTM) values with the uniform cross section of each source. This simple mathematical model confirmed that the recovery coefficient dependence on source size was primarily related to the limited resolution of the detector. Experimental measurements demonstrated that the SPECT resolution for volume sources was sufficient for quantitation, although some limitations exist with respect to source sizes smaller than the detector resolution.     

Comparison of M. longissimus dorsi pigment concentration from implanted and control Angus and Limousin bulls and steers

M. longissimus dorsi total pigment concentration, visual color score and 24-h pH values were evaluated in a 2(3) factorial design that included bulls versus steers, Zeranol implants versus control and Angus versus Limousin comparisons. Bulls had greater total pigment concentration than steers (3.25 versus 2·90 mg/g; P < 0·01) and darker colored lean (P < 0·01). Twenty-four hour pH values did not differ between bulls and steers. Zeranol implanting and breed had no effect on total pigment concentration or visual color score; however, Limousin had higher (P < 0·05) 24-h pH values than Angus. The initial slaughter group (N = 10; average age = 256 days) had 34% less total pigment than the final slaughter group (N = 48; average age = 458 days). The correlation between visual color score and total pigment concentration was -0·65. These results indicate that the darker colored lean from bulls is due in part to an increase in pigment concentration.