Micron (1969)最新文献

Metallographic techniques have been developed for examination of wire wrap sections of neutron irradiated AISI 316 stainless steel from EBR-II. The special etching techniques used for metallographic examination of radiation and thermally induced precipitates, including sigma or chi phases and alpha ferrite, are documented. A description is given of the preparation of standard 3 mm dia TEM foils using a nickel plating technique to increase the effective size of the original 1.1–1.4 mm dia wires.

This paper is a continuation of a series of reports on the design and construction of an atmospheric or environmental SEM. The work described is an extended study of the gas jet developed above the pressure limiting aperture (Bell, 1974; Lacaze et al., 1977). Experiments specifically aimed to establish how the vacuum in the electron optics system was affected by the relative positioning of the objective and pressure limited aperture, as well as the pumping speeds employed, specimen chamber pressure, geometry and size of apertures, and by other means. Further, the nfluence of the jet deflectors, to control the effects of this jet on the microscope system were studied quantitatively using a specifically designed apparatus. In addition, the study of the pressure gradients below the pressure limiting aperture revealed that specimens can be placed as close as radius from the aperture and still experience an almost saturated vapour pressure environment. The results of the present study are currently being used in the design of an optimum detection configuration. A preliminary result has allowed the use of 140 μm pressure limiting aperture to observe specimens at atmospheric pressures as well as the use of low accelerating voltages (e.g. 7 kV) at TV scanning rates to record on video cassette dynamic phenomena, including wetting or recrystallizing salt solutions, etc.

Two morphometric methods, one using a transmission electron microscope (TEM), the other using a scanning electron microscope (SEM), were developed to quantitate the number of surface microprocesses, discs or pores over spherical cells. The number of the surface processes over EL-4 murine T-lymphoma cells cultured in vitro were measured by the two methods. The measurement using TEM yielded 511 ± 45 microprocesses per cell, whereas SEM enumerated 532 ± 25 microprocesses per cell. The method using a TEM, in effect, results in reduction of observed data, and may have an advantage over the method using a SEM when the structures of interest are numerous.

Crystalline suspensions of the proteolytic enzyme papain have been studied by negative staining with sodium phosphotungstate and uranyl acetate, and by thin sectioning. The needle-like crystals of papain exhibit pronounced longitudinal and transverse periodicities and are clearly shown to be formed by the coalescence of parallel bundles of individual fibrils. Optical diffractometry performed on suitable regions of the electron micrographs containing papain crystals have been employed to produce the optical transform for subsequent image filtering. Transverse thin sections of the thicker crystals reveals a complex honeycomb organization with pronounced aqueous channels. This organization is held to be responsible for the varying images of the negatively stained crystals, which result from the varying orientations of the crystal axis relative to the electron beam. It is proposed that papain may represent another useful protein for studying electron microscopically the fibre-to-crystal transformation process, as well as for the understanding of the formation of varying crystalline states.

This investigation deals with correlative scanning-transmission electron microscopic analysis of the mammalian circumventricular organ system CVO. This specilized system of ancient midline regions throughout the third and fourth cerebral ventricle of the brain share many common structural similarities with respect to their vascular, neuronal and glial organization. Areas of analysis of this investigation have included the median eminence, the neural lobe, the organum vasculosum of the lamina terminalis, the subfornical organ and the area postrema. Ample evidence now suggests that these regions of the brain may play an integrative role between blood, brain and cerebrospinal fluid and because they share so many common features, circumventricular organs have been analogized as ‘windows of the brain’. Regions of the cerebral ventricular wall that do not possess neuroendocrine (either real or suspected), possess a dense nap of cilia throughout their mural walls. However, lining ependymal cells of CVO, the so-called ‘tanycyte’, does not exhibit a major population of cilia and instead exhibits a felt work of microvilli organized in a mosaic pattern. These microvilli appear most prominent along the interface of apically oriented cells that constitute the lining of the family of structures collectively referred to as circumventricular organs. Unlike surrounding brain tissue, circumventricular organs do not exhibit the classical blood-brain barrier but possess instead fenestrated capillaries and specialized epennymal cells (tanycytes) that possess tight junctions at their apical (ventricular) sites. Hence in these specialized regions the blood-brain barrier has been shifted from the vascular to the ventricular side and becomes instead a blood-CSF barrier. Coupled with the fundamental differences in the anatomical appearance of the ventricular lumen of circumventricular organs, numerous individual clusters of cells can be seen to reside upon the ventricular surfaces of circumventricular organs. These cells are identified as either populations of quiescent histiocytes or large dense populations of neurons with extensive neuritic arborizations which extend over the ventricular lumen and appear to represent a system of interconnecting axonal processes that may serve to integrate the various circumventricular organs of the third and fourth cerebral ventricle. This investigation deals with the possible role that supraependymal CSF-contacting neurons may play in the synthesis and secretion of neuropeptides into the brain and into the adjacent cerebrospinal fluid.