No abstract

Since it's introduction into TEM in 1986 [1] SSCs have become an effective and easy-to-use solution for acquiring high quality digital images electronically. Their main advantages are excellent linearity, very high dynamic, high sensitivity, and low noise. These advantages have made SSCs a nondispensable tool for quantitative image analysis. Moreover, since SSCs make high quality TEM images available in a computer within fraction of seconds, on-line image processing and software driven automated TEM tuning has become possible [2]. Many of the experiments which are performed nowadays in the area of high resolution, low dose, holographic reconstruction, and EFTEM [3] would not be possible without the digital input coming from SSCs.Like recording images with a film sheet camera, digital recording of images with SSC requires control of the TEM beam blanker (shutter) by the SSC synchronised with the image acquisition process.This blanker (shutter) control is a critical link in the chain to the digital image. Many older TEMs do not have direct access to beam blanking coils, or contrary to modern TEMs their coils are not designed to support hysteresis-free fast beam blanking, what is essential for acquisition of high quality digital images by a SSC.

Large, free-floating crystals of calcium carbonate occur in vacuoles of gastrodermal cells of the hydroid Hydractinia symbiolongicarpus. Here, morphological details about the process by which these cells accumulate and sequester calcium are provided by a cytochemical method designed to demonstrate calcium at the ultrastructural level. Electron-dense material presumably indicative of the presence of calcium was EGTA-sensitive and was shown by parallel electron energy loss spectroscopy (EELS) and energy spectroscopic imaging (ESI) to contain calcium. Calcium occurred in only one cell type, the endodermally derived gastrodermal cell. In these cells, the electron-dense material appeared first as a fine precipitate in the cytosol and nucleus and later as larger deposits and aggregates in the vacuole. During the life cycle, gastrodermal cells of the uninduced planula and the planula during metamorphic induction sequestered calcium. In primary polyps and polyps from established colonies, gastrodermal cells sequestered calcium, but the endodermal secretory cells did not. Our observations support the hypothesis that gastrodermal cells function as a physiological sink for calcium that enters the organism in conjunction with calcium-requiring processes such as motility, secretion, and metamorphosis.

Hairs more than 400 years old of the famous astronomer Tycho Brahe were studied by electron microscopy to evaluate the hypothesis that Johannes Kepler murdered his teacher Brahe by mercury intoxication. The beard hairs showed a well-preserved ultrastructure with typical hair scales and melanosomes. The authors detected an accumulation of electron-dense granules of about 10 nm inside the outer hair scales, but not in the hair shaft and roots. At the places of these heavy-metal-containing granules they detected mercury besides other elements by energy dispersive X-ray analysis (EDX, Oxford, UK) in a field cathode scanning electron microscope (SEM, Gemini, Zeiss). The mercury-containing granules were found over the whole length of hairs, but only in the outer hair scales. Nevertheless, surface coatings of hairs were free of mercury. This distribution of mercury does not support the murder hypothesis, but could be related to precipitation of mercury dust from the air during long-term alchemistic activities.

Extended abstract of a paper presented at MC 2007, 33rd DGE Conference in Saarbrücken, Germany, September 2 – September 7, 2007