Layer line screens

Sakabe, N. A focusing Weissenberg camera with multi-layer-line screens for macromolecular crystallography. J. Appl. Crysi. 16, 542-547 (1983). 

The following sections Al.3.1 and Al.3.2 describe the standard situation where a layer-line screen is used. 

The main book dealing with the precession method is that of Buerger (1964). The precession method is used to record an undistorted representation of a single plane of RLPs and their associated intensities. In order to achieve this the crystal is carefully set so that the plane of the RLPs is perpendicular to the X-ray beam. The normal to this plane, the zone axis, is then precessed about the X-ray beam axis. A layer-line screen with a transparent annulus allows RLPs of the plane of interest to pass through to the film. The screen intercepts all other diffracted rays. The motion of the crystal, screen and film are coupled together to maintain the coplanarity of the film, the screen and the zone. 

Figure 18. Principle of the Weissenberg camera a) tqui-iiiclinalion axis b) Film c) Layer-line screen d) Crystal e) Equi-inclination angle setting...

In the Weissenberg method the crystal is also oscillated about an a.xis. The camera has, in addition, a metal screen with a slit in it that selects out a single layer line and excludes all other layer lines. In order... 

The refractory and acid-resistant lining of vessels shall be inert towards the materials being handled. Surfaces in contact with the reactants shall be corrosion-and erosion-resistant. They can be applied with a layer of screened cpharmaceutical industries or if it forms part ement paste and made smooth. 

Qualitative SAED consists of observation of the pattern of diffraction spots obtained on the TEM viewing screen from a randomly oriented fiber or particle. Such a pattern indicates that the material is crystalline. Chrysotile fibrils, with their cylindrical form, will usually give the same characteristic pattern, corresponding to a 0.73 mn spacing for (0 0 2) planes, and a layer line repeat of 0.53 nm, as well as streaking of the (110) and (130) reflections. These observations and measurements can be made directly from the screen if the appropriate calibrated screen... 

The surface charge density, as given in Eq. (XII. 14), and the adhesion of the toner powder, the quantity of which governs the quality of the image, are determined by the potential of the developing layer. The potential of the blank layer should prevent any sticking of the powder. Consequently, the development effect depends on the difference in potentials between the lined (screened) and blank elements. 

Fig. 7.8. Equi-inclination Weissenberg camera, (a) is the arrangement for recording the zero layer and (b) is the arrangement for recording the first layer photographs. Note in (b), the crystal and the film cassette with the layer screen are rotated through an angle (5 and the layer line selector screen is shifted through a distance of C/2 = r tan <5 for recording the first layer diffraction cone. The incident X-ray beam coincides with the diffraction cone in this equi-inchnation setup...

Set up the printer as before with a screen with the design of the enzyme layer in mesh of size 85 counts/cm and the squeegee (as the ink quantities are small, the flood bar is not used here). Ensure that the pattern in the mesh lines up with the design on the template. 

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