Semipermanent Connections

Semipermanent connections have been required for rework, replacement of components and modules, and repeated connections. Realistic assembly processes for most electronic prodncts are not perfect, so semipermanent terminations are required for rework and replacement of electronic components or modules in standard assembly processes to increase final manufacturing yields. Also, temporary connections are required for testing and adjusting electronic products and modules. These often need 5 to 10 reconnections, with as many as 100 reconnections required in extreme cases. Basic data on typical semipermanent termination technologies are summarized in Tables 64.6 through 64.8. 

The U-tube is permanently or semipermanently deployed in a wellbore to provide the ability to periodically (or continuously) acquire samples. The U-tube is extremely simple, consisting of a loop of tubing, which has a tee at its base, terminating at a check valve that permits fluid to enter the loop of tubing (Fig. 1). A filter at the inlet removes particulates that can interfere with the operation of the check valve. At the surface, the U-tube drive leg is connected to a supply of high pressure N2 that closes the check valve... 

Cyclone separators can be effective as collection devices in SFC. However, they tend to be best suited for semipermanent applications, like preparative-scale chromatography. They are not user friendly for the separation of a large number of different samples in a short time. Each fraction requires a separate cyclone separator. For modest scale separations, the cyclone separators are bulky, with a very large internal surface area, which is difficult to clean out. Because they are subjected to relatively high pressures, they are usually made of stainless steel. Connections are usually made with large-diameter stainless-steel tubing and the whole apparatus is bolted to some sort of rack mount. One could think of this approaches a scaled-down pilot plant. 

A reversible gel based upon dissociable cross-links is characterized by the finite size of the network that is chemically linked into a unit at any instant. In a reversible gel, some of the network connections will always open, close, and interchange. A reversible gel, too, can thus be divided into structural subentities, but the bonds that link these substructures into a macroscopic whole do not possess infinite lifetimes. The coherence of the system depends upon it being contained in a chemically closed, semipermanent, mechanically rigid confinement. A reversible gel cannot, for example, be brought into true (open) swelling equilibrium with an excess of... 

Architecture. Manned space stations are designed to be used as semipermanent habitats and laboratories. Therefore, they are roomier and have more advanced life-support systems and are technologically more complex than other space vehicles. The ISS exemplifies this design consideration It is 240 feet long and 356 feet wide, with more than 12,000 square feet of room in which to live and work. It is also modular, with solar arrays, pressurized living and research modules, connector nodes, storage modules, and other pieces all connected around a central truss system. Each piece of the ISS is launched into space (either aboard a shuttle craft or rocket) and locked into place. The last component of the ISS was scheduled to be added in 2011. 

Bonding ensures that all major parts of a piece of equipment are linked to provide a continuous path to groimd. A bond is a mechanical connection that provides a low-resistance path to current flow between two surfaces that are physically separated or may become separated. A bond can be permanent, such as one in which the coimection is welded or brazed to the two surfaces, or it may be semipermanent, bolted or clamped where required. 

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