Molecular weight determination by scanning transmission electron microscopy

A scanning transmission electron microscope is employed to determine the mass of biological macromolecules. Elastically scattered electrons are collected by an annular detector that is capable of counting single electrons. Off-line processing of these dark field micrographs stored on a magnetic tape is accomplished by a mini-computer. It allows the number of electrons scattered by spherical or filamentous proteins to be evaluated. The calibration factor relating the number of scattered electrons to the mass of the protein is derived from scattering theory and is experimentally determined from biological macromolecules of known mass. Mass-loss kinetics of biological specimens due to the electron beam are measured for various protein structures. The application of this method is illustrated by determination of the mass of an oligometric protein (major phage T4 head protein) and the mass per unit length of a filamentous protein aggregate (F-pili). The unique possibilities of this new technique as well as its limitations are discussed.

Selected examination findings related to periodontal disease among adults, United States - 1960-1962

In a previous report the Health Examination Survey estimated the prevalence among U.S. adults of inflammatory disease of the anatomic structures that support teeth. Based on examinations conducted during 1960-62, the estimates underscore not only the high prevalence of periodontal disease but also its wide range of distribution throughout the United States. About 44 million adults aged 18-79 years had gingivitis without obvious pocket formation, the report estimated, and about 23 million had chronic destructive disease with one or more pockets diagnostic of advanced periodontal disease. Distinct patterns of distribution prevailed: more disease was generally present in older people than in younger ones, in men than in women, and in Negro adults than in white. In addition, men and women who were economically and educationally more advantaged usually had less periodontal disease than others. Oral hygiene among sample men and women who had one or more of six specified teeth was also evaluated. As foreseen, both the prevalence and severity of periodontal disease increased as oral hygiene worsened. Demographic differences in the distribution of periodontal disease were either largely or fully leveled when allowance was made for variations in oral hygiene. However, among people with equivalent levels of oral hygiene, older men and women had more periodontal disease than younger men and women. Briefly, both age and oral hygiene emerged as important factors, each of which was related independently of the other, in the prevalence and severity of periodontal disease.

Particle size analysis using computer-synthesized holograms

A holographic correlation method permits the determination of the diameter and size distribution of suspended particles with diameters from 1 microm to 10 microm. The method uses synthetic holograms calculated from the Mie scattering theory.

Laser machining with modulated zone plates

Machining of small holes with arbitrary contours can be performed by focusing a laser beam with a modulated zone plate (MZP). MZP's use the structure of the Fresnel zone plate as the carrier of a modulation function, which contains complete information about the contour to be machined. Spherically corrected MZP's produce aberration-free images within a field angle of 10(-3) rad. It is shown that the background noise due to higher diffraction orders is unimportant under typical machining conditions. A manufacturing procedure for high resolution MZP's with up to 2500 zones etched in chromium or quartz layers deposited on glass substrates is discussed. As in-line holograms have properties similar to MZP's, a simple method of recording wavelength-shift corrected in-line holograms is described. Experiments performed with a stable single-mode Nd(3+)-YAG laser demonstrate that the MZP can be important tool for laser machining purposes.

Additional filters enhancing the sensitivity of an optical correlator

The influence of additional filters upon the output of an optical correlator is studied for the case of a spatial filter measuring the size of rectangles. Additional filters leading to increased sensitivity are derived by means of a series expansion. One type of additional filter, consisting of several transparent slits, yields a linear relation between output signal and the deviation from the desired size. The other additional filter, effecting a quadratic output characteristic, is a properly dimensioned bandpass. Experimental results demonstrate the enhancement of sensitivity achieved with additional filters. As this method can easily be extended to a correlator measuring the diameter of circular apertures, additional filters may be of interest in the field of automatic production control.

Computer-drawn modulated zone plates

The structure of Fresnel zone plates is considered as a binary carrier of complex modulation functions. Due to the Fourier-transforming roperties of this particular carrier, any original object can be reconstructed with a simple monochromatic point source using no additional optics. An analysis of modulated zone plates (MZP) verifying their Fourier-transforming and imaging properties is given. experiments were performed with several types of computer-drawn MZP's. Results illustrating the flexibility of this method are in good agreement with theory. The simple method of reconstructing and scaling the object intensity distribution, the high efficiency, as well as he resistance against high laser intensities show the MZP to be a convenient tool for laser micromachining of patterns with optional shape.