Spot pattern

The diffraction pattern observed in LEED is one of the most connnonly used fingerprints of a surface structure. Witii XRD or other non-electron diffraction methods, there is no convenient detector tliat images in real time the corresponding diffraction pattern. Point-source methods, like PD, do not produce a convenient spot pattern, but a diffrise diffraction pattern that does not simply reflect the long-range ordermg. 

Consequently, when D /Dj exceeds the critical value, close to the bifurcation one expects to see the appearance of chemical patterns with characteristic lengtli i= In / k. Beyond the bifurcation point a band of wave numbers is unstable and the nature of the pattern selected (spots, stripes, etc.) depends on the nonlinearity and requires a more detailed analysis. Chemical Turing patterns were observed in the chlorite-iodide-malonic acid (CIMA) system in a gel reactor [M, 59 and 60]. Figure C3.6.12(a) shows an experimental CIMA Turing spot pattern [59]. 

Figure C3.6.12 a) Turing spot pattern in the CIMA reaction. (A) Tio-temporal turbulence near the Turing bifurcation. Reproduced by pennission from Ouyang and Swinney [59].

TEM offers two methods of specimen observation, diffraction mode and image mode. In diffraction mode, an electron diffraction pattern is obtained on the fluorescent screen, originating from the sample area illuminated by the electron beam. The diffraction pattern is entirely equivalent to an X-ray diffraction pattern a single crystal will produce a spot pattern on the screen, a polycrystal will produce a powder or ring pattern (assuming the illuminated area includes a sufficient quantity of crystallites), and a glassy or amorphous material will produce a series of diffuse halos. 

Various electron diffraction techniques are available on modem transmission electron microscopes. Selected-Area Electron Diffraction (SAED) and Microdiffraction are performed with a parallel or nearly parallel incident beam and give spot patterns. Convergent-Beam Electron Diffraction (CBED) and Large-Angle Convergent-Beam Electron Diffraction (LACBED) are performed with a focused and defocused convergent beam... 

Figure 1. Electron diffraction pattern examples a - spot pattern from a single crystal, b -oblique texture pattern tilted by 60°, c - powder ring pattern.

The spotting pattern was created according to the spotter program. 

For example, in the spot pattern shown in Fig. 11.1b, the beam enters the cell at the gap marked 0 in the field mirror and, after multiple reflections, exits at the gap in the field mirror on the opposite side, marked 28. A total of 28 passes (or 2n + 2, where n is the... 

An astigmatic variant of the Herriott cell designed for use in ambient air studies is shown in Fig. 11.2a and described by McManus et al. (1995) and Zahniser et al. (1997). In this design, the two mirrors have different radii of curvature, giving the spot patterns shown in Fig. 11.2c. The spots more evenly fill the mirror, so that for a given number of passes, the spots are more widely spaced, or conversely, more passes can be obtained without problems of beam overlap (McManus et al., 1995). 

Spot patterns should always be assessed relative to the standard mixture. In general, keratan sulfate will migrate with the leading front, while chondroitin-6-sul-fate should be located between fronts 5 and 6, chondroitin-4-sulfate between fronts 4 and 5, heparan sulfate between fronts 3 and 4, hyaluronic acid between fronts 2 and 3, and dermatan sulfate between fronts 1 and 2. 

Procedure. The site was developed on a five-spot pattern about 25 ft square, as shown in Figure 2. The wells were rotary drilled with water and completed with 50 ft of 7-in. casing and cemented to the surface. A 6%-in. hole was drilled below the casing to a total depth of 100 ft in the oil shale. Two additional wells were drilled off pattern as observation wells. A Fischer assay determined the oil yield of the section as 19.0-26.5 gal/ton. Two sand-propped hydraulic fracture treatments were applied for emplacing NG1 in the formation. 

Procedure. Site Preparation. A five-spot pattern of test wells (Figure 4) was drilled to approximately 57 ft and completed with 7-in. casing cemented to the surface. The wells, deepened to 100 ft with a 6%-in. bit, were tested to determine the extent of air communication between the center well (well 5) and the surrounding wells. These tests indicated fractures 1-3 ft in height between depths from 67 to 90 ft. 

During the second step of the fracturing experiments at this site, 60% dynamite was detonated in the five wells to relieve stress conditions in the block of oil shale. Each of the wells in the 25- by 25-ft five-spot pattern was loaded with 45-lb charges of 60% dynamite on detonating cord with electric caps attached and detonated simultaneously (shot B). 

Figure 5. Position of explosive charge in sequence of wellbore shots in five-spot pattern, Rock Springs site 5...

The completed site contained 10 pattern wells for explosive-fracturing research. Six wells were drilled on 50-ft spacing to form a rectangle with three wells on a side. The remaining four wells were drilled on 25-ft spacing to form a five-spot pattern (Figure 6). All wells were completed similarly to the earlier described test wells. 

The first series of explosive tests on the site was performed on the wells in the five-spot pattern. The amount of TNT used in each well was calculated from total-depth and caliper-log measurements. The accumulated water was bailed prior to lowering the priming devices and filling the wellbores with TNT. 

Table I. Shooting Data, First Shot, Small Five-Spot Pattern, Green River Site 1...

Wells 3,5, and 6 were reloaded with 1860 lb of TNT and shot (Table III). After cleanout and after caliper logs were obtained, airflow tests were run on the five-spot pattern wells to determine the relative extent of fragmentation and improvement in communication between wells. 

The final explosive-fracturing test performed on this site was a simultaneous shot detonated in the wells of the five-spot pattern. Wire-line measurements were obtained to determine total depth, and caliper logs were run to determine wellbore enlargement from which to calculate the amount of TNT to fill each well. Water was swabbed and bailed... 

The organic matrix follows the same pattern. By means of electron diffraction analysis it can be shown that the protein matrix is and remains crystalline and that the structural order of the diffraction pattern is that of a microcrystalline film of gold (Fig. 23)224). It is remarkable that the matrix proteins in other species also produce a single crystal spot pattern. This implies that isolated pieces of organic matrix which are in the order of a few microns thick represent single crystals. Whatever the term single crystal" may mean to the various researchers43, in the context... 

Displacement of oil in petroleum reservoirs by water or chemical flooding (five-spot pattern)... 

Figure 11.4 Displacement of oil in petroleum reservoirs by water or chemical flooding using a five-spot pattern. From Ling et. a. [223], Copyright 1987, Royal Society of Chemistry.

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