Background grains

Apparent in Fig. 12.6 is the group of unlabelled cells. Such cells usually average less than one grain per cell and a similar distribution 

Higher backgrounds are found (1) if the emulsion used is old or has been stored adjacent to a radioactive source, e.g. 32 P (2) if exposure times are long or (3) if removal of tritiated precursors or acid soluble components has been inadequate. 

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Deuchar EM. Staining sections before autoradiographic exposure excessive background graining caused by celestin blue. Stain Technol 1962 37 324. 

Figure 7.20. The observed and calculated powder diffraction patterns of NiMn02(OH) after preferred orientation, coordinates of all atoms and the overall displacement parameter were refined in addition to the scale factor, unit cell dimensions, background, grain size and strain effects, and peak asymmetry. The insert clarifies the range between 70 and 90° 20.

We shall describe an ISH procedure in which the same nboprobes can be used either on sections of samples prefixed in paraformaldehyde and embedded in paraffin, or on cryosections of directly frozen samples. Although ISH using paraffin-embedded material has been commonly used to date, we have noticed that ISH on cryosections results in a far higher sensitivity. This is due to both lower background grain levels and higher signal intensities. In particular, ISH on cryosections has allowed the detection of specific isoforms of RAR mRNAs (unpublished results from our laboratory), which had been... 

Expt. Background (grains/nucleus-sized area) ... 

Las but not least, sample preparation is also an important issue. If we want to examine nanocrystalline powder samples. The grain size must be just a few nanometers, the layer, formed by these nanocrystals must be as thin as possible (to minimize dynamic difiraction), continuous and self-supporting. In many cases not all these requirements are fulfilled simultaneously. The nanocrystalline material to be studied is frequently present on a thin supporting carbon layer. In such cases peak decomposition can not yield an acceptable fit unless the presence of the amorphous material (in the form of a few diffuse rings) is taken explicitly into account in the model to be fitted. The size of the background is also affected by scattering in such a carbon support. 

When all the phases present were identified, we can quantify their volume fraction in the analyzed volume similarly to the way the Rietveld-method is used for phase analysis in XRD. A whole profile fitting is used in ProcessDifraction, modeling background and peak-shapes, and fitting the shape parameters, thermal parameters and volume fractions. Since the kinematic approximation is used for calculating the electron diffraction intensities, the grain size of both phases should be below 10 nm (as a rule of... 

Polished thin sections or iron oxides grains polished in epoxy mounts were analyzed using Universite Laval CAMECA SX-100 5-VVDS electron microprobe under a beam of 15 kV at 100 nA, using a range of natural and synthetic standards. After counting over the peak for 20 to 30 sec, background is measured on both sides for 10 sec. These settings yield minimum detection limits (mdl) as low as 20 ppm for elements such as K, Ca, Al, Si, Ti and Mg, 50 ppm for Mn, Cr and V, 200 ppm for Cu,... 

C. albicans formed crystals of the regular shape, tri- and tetrahedral, lateral lines were straight and parallel to each other. There were either no branches or there were 1-2 short branches. The central part of the crystals was clear, background was fine-grained. 

C. tropicalis formed crystals of the awkward shape, with shifted centers and indented edges. There were lateral branches, background was fine-grained. 

C. krusei formed large crystals of the regular shape, tri-and tetrahedral, with well-expressed centers and dense banding. Background was fine-grained. 

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