Spiral pattern

The same principles apply to table feeders. The sldrt is raised above the table in a spiral pattern to provide increased capacity in the... 

FIG. 21-29 Table feeder. The sldrt is raised in a spiral pattern for increased capacity in the direction of rotation. Couitesy of Chemical Engineering.)... 

Seams. As a defect, a seam is distinct from the seam resulting from a welding process. Seam defects can be found in nonwelded (seamless) tubes. They can originate from blow holes or nonmetallic inclusions in the ingot and are caused by crevices that have been closed by some rolling process but remain unfused. At times, they will appear in a spiral pattern in tubes. Seams can be very tight and appear as hairlines on the surface. They can cause failure when the component is pressurized. 

Dry gas seals are in the positive seal class and have the same basic design features as mechanical face seals with one significant difference. The dry gas seal has shallow grooves cut in the rotating seal face located part way across the face. The grooves may be in a spiral pattern the exact location and pattern vary from one manufacturer to another. Lubrication and separation is effected by a microscopically thin film of gas. This implies some finite amount of leakage, which is quite small but must be accounted for in the design. 

In either construction, each element of the APH can be assigned a unique turn (/)10 and angular step ( -n) along the helical pathway, measured from the s-block origin that forms the natural spine of the spiral pattern (the heavy vertical line in Fig. B.3). For example, the element chromium (Cr) can be denoted as the t5/d4 element, to locate it at the d4 angular step (the fourth element of the d block) on the t5 tier of the helix. In this manner, the distinctive form, topology, and orientation of the APH effectively complement... 

Figure 8.26 Schematic of two common knob-type mixers a) a straight knob mixer with the knobs in the same angular position, and b) a pineapple mixer with the knobs positioned in a spiral pattern in the same direction as the main flights of the screw channel...

When the step separation is wide enough, typical spiral step patterns observable by optical microscopy may appear, but if the separation becomes narrower than the resolution power of the optical microscope, the spirals appear in the forms of polygonal pyramids or conical growth hillocks. Even if spiral patterns are not directly observable, we may assume that these growth hillocks are formed by the spiral growth mechanism. Examples representing the two cases are compared in Fig. 5.8. 

Figure 5.8. (a) Typical spiral pattern (phase contrast photomicrograph of (0001) face of Sic grown from the vapor phase), and spiral growth hillocks which appear as (b) polygonal and (c) conical pyramids due to narrow step separation. Part (b) is a differential interference photomicrograph, (1010), and part (c) is a reflection photomicrograph, (1011), of hydrothermally synthesized quartz. 

Figure 5.9. Eccentric spiral pattern on a (0001) face of SiC, due to a supersaturation gradient over the surface [13]. The spiral center is indicated by c, and the arrows a, b show the directions of eccentricity (where the white arrow refers to the center of the crucible, and the black arrow refers to the wall).

In volcanic rocks formed by the solidification of magma near the Earth s surface, small cavities of millimeter to centimeter order are often present, in which idiomorphic crystals of phlogopite and hematite occur. All these crystals grown from the vapor phase show typical spiral patterns. However, they grow in a much-reduced free space as compared to the case of pegmatite, and this characteristic is well represented on their surface microtopographs. 

Compound 114d possesses significantly lower transition temperatures (Scheme 60) due to the branched side chains [126]. A columnar phase is present even below room temperature. At 14 °C, anew chiral columnar phase was observed while above 111 °C, an achiral columnar rectangular phase was observed. The spiral-pattern texture of 114d in the chiral Col mesophase is shown in Fig. 17. 

Fig. 17 Spiral-pattern texture of 114d in the Col phase. Reproduced by permission of Taylor Francis (www.informaworld. com) from [127]...

The strange carbon blast was produced by binary star 4U 1820-30, which consists of a dwarf star orbiting a neutron star. Gas from the dwarf flows in a spiral pattern around the neutron star. When some of the dwarf s gas collides with the neutron star s surface, a compressed slurry of hydrogen and helium is formed. Pressures and temperatures can get sufficiently high in the slurry layer that the elements flash-fuse in a thermonuclear explosion. Each blast leaves carbon, one of the byproducts of helium fusion. Gradually a layer of carbon several hundred meters thick reaches a critical temperature and ignites a carbon bomb that rages for hours. [For more information, see Robert Irion, Astronomers spot their first carbon bomb, Science 290(5495) 1279 (November 17, 2000).]... 

The principal features of the spiral structure are believed to be maintained by a pattern of density waves. This pattern rotates about the galactic center like a rigid body with an angular velocity that is lower than that of most of the material. Thus, the material of the Galaxy (i.e. both stars and gas) flows through the pattern and as it enters the density wave, the gas is strongly compressed. There are also less important elements of the spiral pattern that rotate with the material these are called material arms, as against density-wave ... 

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