Surface recession measurement

The erosion yield of a polymer is typically measured by two methods (1) recession and (2) mass loss. Recession measurements are made by masking an area of a sample surface from attack and measuring the step height difference between exposed and unexposed areas. The thickness loss divided by the exposure fluence is the erosion yield. Mass loss measurements are made either by weighing a sample before and after exposure or by monitoring the mass loss in situ of a material that was coated onto a quartz crystal microbalance. Care must be taken in mass loss measurements to ensure that outgassing from the material in the vacuum of the exposure environment does not affect the results. The calculation of the erosion yield from a mass loss measurement requires knowledge of the density of the material and the surface area exposed, as well as the exposure fluence. 

Analytical results for sulfate ions are for the net change in rainfall composition, after the rainfall flows over the surface of the exposed stone (Tables I and II). The net concentration, resulting from the interaction of rain with the stone surface, is calculated by subtracting the blank-sample concentration value from the value measured for the stone runoff. For very small rain amounts (typically 2 to 4 millimeters), blank volumes were too small to allow complete chemical analysis. Sulfate ion net concentration, in excess of that possible from sulfate loading, was calculated to identify the presence of soluble sulfate-containing minerals on the rock surface. Loss of rock mass, measured by the calcium concentration in the runoff, is expressed as surface recession, in micrometers of rock surface lost per rainstorm. The net calcium concentration in the runoff solution is converted to an equivalent volume of rock removed this result divided by the surface area of the exposed rock, yields a measurement of surface recession. ... 

Relation between environmental variables and surface recession. Carbonate-rock surface recession and the environmental variables measured in this program (i.e., rain amount, rain pH, hydrogen ion loading to the rock surface, and antecedent sulfur dioxide) exhibited a range of values at the North Carolina site during the last half of 1984. To examine qualitatively the relation between... 

Surface Roughening/Recession. Two approaches to measurement of surface recession were explored. One method applied a classical form of optical interferometry to optically smooth samples of stone in an attempt to measure results after brief exposure of the surfaces to rain this approach was only partially successful and will be only... 

Another source of increased drag involves the external-surface details. In this regard, stand-alone bumpers, externally protruding door handles, and running boards alongside the passenger compartment to facilitate entity, all of which were once universal, have disappeared. Flush rather than recessed side windows have come into recent use. On the other hand, external rear view mirrors, which increase drag, have been added as a safety measure. 

The upper surface of the baseplate s center is a recessed socket with a latching collar to accept and retain the round base of the barrel, which is free to pivot in all directions. When in use, the barrel may be adjusted vertically from 40° to 85°.Transverse or horizontal movement is 5" total, or 2.5" left or right of center, as measured at the transverse mechanism. The underside of the baseplate is fitted with four triangular feet that dig firmly into the ground to stabilize the mortar under fire.The front edge carries an additional row of four smaller feet that aid in stability.The four main feet,as well as the central socket area, are tied together and reinforced with several gussets and braces. 

In devising a scheme for monitoring the rate of deterioration of the sandstone, the assumption was made that any effect that atmospheric pollutants may have on the stones integrity will appear at or near the surface. It is not a common occurrance that masonry is saturated throughout by water. Consequently, an adequate measure of erosion is the rate of recession of the surface. Here, the bonding material is dissolved or disrupted by repeated exposures to moisture which may contain chemicals which accelerate the process. The rate of recession is characterized by the rate at which the loosened quartz grains are subsequently removed. 

Figure 5. Sections of briquettes in Lucite holders for atmospheric exposure in test racks prior to measurements of stone surface roughness and recession. Teflon bars protect portions of surfaces for reference in measurements by laser holographic moire profiling method.

If a small (submicrometer) tip is to be used in quantitative measurements, it is important to show that the metal surface is not recessed into the insulator since the mass transport coefficient will be altered. This is possible via a study of the approach curve a recessed tip does not produce as large a positive feedback [26]. Recessed tips have also been produced intentionally for single molecule experiments [79, 80]. Fan and coworkers [80] simulated a special case of the recessed electrode with the radius of the circular hole in the insulator equal to the disk radius. An analytical approximation for recessed tips with the hole in the insulator sheath different from the disk radius is also available [25]. The feedback effect is also reduced for tips, which are conical or spherical caps, but the shape of the approach curve provides some information on the tip geometry, for example, the solid angle [26]. Accurate numerical simulations of such tips by the finite difference method are more costly than for microdisks, but have been... 

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