Pancreatic lipase hydrolysis of triglycerides by a semimicro technique

Procedures are described for rapid lipase hydrolysis of triglycerides, isolation of the hydrolytic products by TLC and their conversion to methyl esters and fatty acid analysis by GLC. The techniques are applicable to a few mg of triglycerides or fats. Examples of data obtained with purified triglycerides indicate that the specific action of pancreatic lipase for the 1,3 ester groups is nearly absolute and the technique may be used as a criterion of purity of di- and tri-acid triglycerides. Ca. 83% of the palmitic but only 10~12% of stearic and C₁₈ unsaturated acids of commercial lard occur in 2-position. Presented in part at the AOCS Meeting, Minneapolis, 1963. A laboratory of E. Utiliz. Res. & Dev. Div., ARS, USDA.     

Characterization of supported cylinder-planar germanium waveguide sensors with synchrotron infrared radiation

Cylinder-planar Ge waveguides are being developed as evanescent-wave sensors for chemical microanalysis. The only non-planar surface is a cylinder section having a 300-mm radius of curvature. This confers a symmetric taper, allowing for direct coupling into and out of the waveguide's 1-mm(2) end faces while obtaining multiple reflections at the central <30-microm-thick sensing region. Ray-optic calculations indicate that the propagation angle at the central minimum has a strong nonlinear dependence on both angle and vertical position of the input ray. This results in rather inefficient coupling of input light into the off-axis modes that are most useful for evanescent-wave absorption spectroscopy. Mode-specific performance of the cylinder-planar waveguides has also been investigated experimentally. As compared to a blackbody source, the much greater brightness of synchrotron-generated infrared (IR) radiation allows a similar total energy throughput, but restricted to a smaller fraction of the allowed waveguide modes. However, such angle-selective excitation results in a strong oscillatory interference pattern in the transmission spectra. These spectral oscillations are the principal technical limitation on using synchrotron radiation to measure evanescent-wave absorption spectra with the thin waveguides.     

Biometric verification with correlation filters

Using biometrics for subject verification can significantly improve security over that of approaches based on passwords and personal identification numbers, both of which people tend to lose or forget. In biometric verification the system tries to match an input biometric (such as a fingerprint, face image, or iris image) to a stored biometric template. Thus correlation filter techniques are attractive candidates for the matching precision needed in biometric verification. In particular, advanced correlation filters, such as synthetic discriminant function filters, can offer very good matching performance in the presence of variability in these biometric images (e.g., facial expressions, illumination changes, etc.). We investigate the performance of advanced correlation filters for face, fingerprint, and iris biometric verification.     

Estimation of surface pose with a physically-based ultrasonic image model

State-of-the-art approaches to shape analysis in medical images use a variety of sophisticated models for object shape. We have developed an image model that permits the application of these approaches to ultrasonic images, with detailed methods for representing rough surfaces. Our physically-based, probabilistic image model incorporates the combined effects of the system point-spread function (PSF), the tissue microstructure, and the gross tissue shape. At each image pixel, the amplitude mean and variance are computed directly from the model, characterizing the combined influence of shape, microstructure, and system PSF. Calculation of the SNR0 is used to further classify each pixel as Rayleigh- or non-Rayleigh-distributed. This characterization was used here to generate a data likelihood representing any set of images of a given surface by a probability density conditioned on the surface pose, or rotation and translation. The utility of this likelihood was demonstrated by applying maximum likelihood estimation to infer the pose of a cadaveric vertebra from simulated images of its surface. Successful results were achieved using derivative-based optimization algorithms for a data set of only three images. With a quasi-Newton BFGS algorithm, error in 15 of 20 trials was less than 0.4 degrees in rotation and 0.2 mm in translation. Estimation was inaccurate in only 1 of 20 trials. These results illustrate the potential of a physically-based image model in a rigorous approach to image analysis and also serve as an example of quantitative assessment of the model via performance in a specific application.     

X-ray phase vortices: theory and experiment

We review the current work on x-ray phase vortices. We explain the role of an x-ray vortex in phase recovery and speculate on its possible applications in other fields of x-ray optical research. We present our theoretical understanding of the structure of phase vortices and test these predictions against experiment. We present experimental observations of phase vortices with charge greater than 3 and observe that their propagation appears to be consistent with our theoretical models.     

Kinetics of thermal damage to a collagenous membrane under biaxial isotonic loading

Prior isothermal uniaxial isotonic tests on tendons reveal that higher temperatures hasten the rate of thermal denaturation whereas larger mechanical loads delay it; moreover, these findings suggest a time-temperature-load equivalency whereby similar levels of denaturation, as reflected by tissue shrinkage, can be attained via many combinations of heating time, temperature level, and mechanical loading. Yet, most tissues and organs experience multiaxial loads in vivo, and their microstructure differs significantly from that of tendons, thus, we must also evaluate the effects of multiaxial stresses on the kinetics of denaturation in other tissues. In this paper, we describe a new experimental approach for performing isothermal biaxial isotonic tests on thin sheet-like specimens and we report effects of various thermomechanical loads on the rate and amount of multiaxial shrinkage of bovine epicardium. Consistent with uniaxial studies, epicardial shrinkage generally increased sigmoidally with heating time, and a characteristic heating time revealed increases in the rate of shrinkage with higher temperature and decreases with larger biaxial loads. Although this characteristic time exhibited an Arrhenius-type character, time-temperature-load equivalency was not obtained when scaling time with this metric. General multiaxial thermomechanics is thus too complex to explain via a simple extension of uniaxial findings on tendons and there is a pressing need for more data and an appropriate theoretical framework.