Scattering characteristic

A final practical note involves instrument intensity measurement calibrations. The intensity measurement is self-calibrating relative to the incident beam from the source. However, measurements typically have a dynamic range of 10 -10 , and care must be taken to insure the detection system is linear. A method of calibrating the scatterometer is to characterize a diffuse reflector having a known scattering characteristic. For example, a surface coated with BaS04 makes a nearly Lambertian scatterer, which has a BRDF of 1/Jt at all angles. 

Fig. 8—9. The dependence of the niobium line intensity on the scattering characteristics of the matrix. (Courtesy of M. L. Salmon, Fluo-X-Spec Analytical Laboratory, Denver, Colo.)...

Matrix scattering characteristics, dependence of niobium line intensity on, 234... 

This paper will be limited to a discussion of our packed column studies in which we have addressed attention to questions regarding, (a) the role of ionic strength and surfactant effects on both HDC and porous packed column behavior, (b) the effects of pore size and pore size distribution on resolution, and (c) the effects of the light scattering characteristics of polystyrene on signal resolution and particle size distribution determination. 

Howell, S. G., and B. J. Huebert, Determining Marine Aerosol Scattering Characteristics at Ambient Humidity from Size-Resolved Chemical Composition, J. Geophys. Res., 103, 1391-1404 (1998). 

Another colloidal system with light scattering characteristics that have been widely studied is the so-called monodisperse sulfur sol. Although not actually monodisperse, the particle size distribution in this preparation is narrow enough to make it an ideal system for the study of optical phenomena. 

Fixation of cells in l% formaldehyde in PBS will change their light scatter characteristics slightly. Therefore, when comparing samples over a time-course, it is important that all samples should be fixed for at least 24 h before analysis. 

If the basis contains atoms of different elements it is useful to separate the phase shifts due to the geometric arrangement from the scattering characteristics of the atoms. If rj is the vector from the origin of the unit cell to the center of atom j (denoting the position of atom j within the unit cell), and nj(r - rj) is the contribution of atom j to the total electron density at r, the structure factor can be written as ... 

Solids. Conventional near-infrared reflectance analyzers use a variety of methods to position the sample into the incident collimated beam and collect reproducibly the diffusely reflected radiation to measure the absorption which takes place in the body of the sample traversed. Solid samples are ground with care to achieve reproducible and reasonably uniform granulation for calibration and analysis measurements. The overall scattering characteristics of the sample which shift the reflectance baseline and control the depth of sample penetration and opportunity for absorption become a part of the method and the empirical analytical equation (6,9). Solid sampling is summarized on the following table. 

Fig. 6.11. Back-gating from CD 14 fluorescence to determine the scatter characteristics from monocytes. Such back-gating facilitates the placing and then evaluation of a monocyte scatter gate.

Back-gating Back-gating is a strategy by which the fluorescence of stained cells within a mixed population is used to determine the side scatter and forward scatter characteristics of those cells. This is in contrast to traditional gating, whereby scatter characteristics are used to delineate cells whose fluorescence characteristics are then determined. 

Fixation Fixation is the process by which the protein of cells is denatured, or cross-linked, and preserved. Fixation in flow cytometry is used to inactivate hazardous biological material and also to preserve stained cells when there is not immediate access to a flow cytometer. Fixation is also important in preserving proteins before detergent permeabilization for intracellular staining. Formaldehyde is often the fixative of choice for flow cytometry because it preserves the forward and side scatter characteristics of cells (but does cause some increase in their autofluorescence). 

Monocyte Monocytes are a class of white blood cells that co-purify with lymphocytes in commonly used density gradient procedures. They tend to be promiscuously sticky for the nonspecific (Fc) ends of monoclonal antibodies and therefore can lead to misleading results in analysis of leukocyte subpopulations unless their Fc receptors are blocked in the staining procedure. Monocytes differ from lymphocytes in their forward and side scatter characteristics. 

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