Slip face

Free dunes have no fixed position, but migrate downwind by erosion on the gently inclined windward side and deposition on the leeward side (slip face) in the same way as described for fixed dunes. The smallest free dunes are common wind ripples that measure only a few centimeters in height. Large dunes are found in extensive dune areas in deserts, in sand seas known as ergs . 

As the sand moves over the summit dq/dx is negative and deposition is indicated. This deposition does not take place uniformly over the lee side of the dune, but just over the brink. This deposition continues until the angle assumed by the deposited sand with the horizontal approaches the angle of repose (about 34 deg for sand) and then the deposit slides down. Thus the lee slope, or slip-face as it is called, never exceeds the angle of repose. 

Thus the higher the dune, the less is its rate of movement, subject of course to the supposition that all the sand moved from the windward side has been deposited on the slip-face. As a corollary we also conclude that, if the dune decreases in size for any reason, its rate of. travel increases. As an example of the magnitude of the quantities involved in the present discussion, suppose that with a wind intensity of 14 m per sec, q = 0.46 ton per meter-width per hr. If pa = 1.7 and H = 15 m, we then have from Eq (19-29) that... 

Dune cresb Slip faces - Blowouts Aeolianite (U Sand dunes (general) [ Oblique dunes 3 Parabolic dunes... 

In a toroidal traction drive, toroidal input and output disks face one another, separated by a number of rollers that contact the toroid surfaces. The rollers are mounted so that they can he tilted to vaiy the radius from the centerline of the disks where they contact the toroids, and therefore determine the input/output speed ratio of the rotating disks. A substantial axial force must be applied to the disks to prevent the rollers from slipping on the disk surfaces. To avoid excessive losses when the torque transmitted is low, this force needs to he modulated in proportion to the torque transmitted. 

To illustrate this, take the situation in a very common and relatively simple metal structure, that of copper. A crystal of copper adopts the face-centered cubic (fee) structure (Fig. 2.8). In all crystals with this structure slip takes place on one of the equivalent 111 planes, in one of the compatible <110> directions. The shortest vector describing this runs from an atom at the comer of the unit cell to one at a face center (Fig. 3.10). A dislocation having Burgers vector equal to this displacement, i <110>, is thus a unit dislocation in the structure. 

The streamlines over the surface of the RRDE are very similar to those at the face of an RDE (see Figure 7.2). Therefore, mixing occurs as solution is drawn across the surface of the electrode solution is drawn in from the bulk at the same time as solution containing electrogenerated material is lost to the bulk. In effect, we demonstrate the old saying, there s many a slip twixt cup and lip . 

Beside dislocation density, dislocation orientation is the primary factor in determining the critical shear stress required for plastic deformation. Dislocations do not move with the same degree of ease in all crystallographic directions or in all crystallographic planes. There is usually a preferred direction for slip dislocation movement. The combination of slip direction and slip plane is called the slip system, and it depends on the crystal structure of the metal. The slip plane is usually that plane having the most dense atomic packing (cf. Section 1.1.1.2). In face-centered cubic structures, this plane is the (111) plane, and the slip direction is the [110] direction. Each slip plane may contain more than one possible slip direction, so several slip systems may exist for a particular crystal structure. Eor FCC, there are a total of 12 possible slip systems four different (111) planes and three independent [110] directions for each plane. The... 

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