Clamped crystal

If we arrange the experimental conditions such that we apply an electric field at the same time as we mechanically hinder the crystal s deformation (this is called the clamped crystal condition), then y = 0, and... 

Thus we see again that the coupling raises the transition temperature. As an example, the paraelectric-ferroelectric transition point in a free crystal KDP lies 4 °C higher than for a clamped crystal. The reason that the Curie point is lower in the clamped crystal is that the mechanical clamping eliminates the piezocoupling. 

B Guenther, R Onrust, A Sail, M O Donnell, J Kuriyan. Crystal structure of the 5 subunit of the clamp-loader complex of E. coli DNA polymerase III. Cell 91 335-345, 1997. 

The screw clamp may be adjusted so that there will be a spattering on the upper, cool part of the flask, while the pressure is still maintained below 30 mm. Under these conditions, the initiation of crystallization is speeded. 

The crystallization is responsible for the quick grab of polychloroprene adhesives. This rapid bond strength development allows the formation of immediate dry bonds without the need of clamping or pressing. 

The crystallization kinetics defines the open time of the bond. For automated industrial processes, a fast crystallizing backbone, such as hexamethylene adipate, is often highly desirable. Once the bond line cools, crystallization can occur in less than 2 min. Thus, minimal time is needed to hold or clamp the substrates until fixturing strength is achieved. For specialty or non-automated processes, the PUD backbone might be based on a polyester polyol with slow crystallization kinetics. This gives the adhesive end user additional open time, after the adhesive has been activated, in which to make the bond. The crystallization kinetics for various waterborne dispersions were determined by Dormish and Witowski by following the Shore hardness. Open times of up to 40 min were measured [60]. 

FIGURE 9.4 The direct force measurement apparatus shown here ean measure the forees between two eurved molecularly smooth surfaces in liquids. Mica surfaces, either raw or eoated, are the primary surfaees used in this apparatus. The separation between the surfaces is measured by optieal teehniques to better than 10 nm. The distance between the two surfaces is controlled by a three-stage meehanism that ineludes a voltage-driven piezoelectric crystal tube supporting the upper mica surface this crystal tube can be displaced less than 10 nm in a controlled fashion. A force-measuring spring is attached to the lower mica surface and its stiffness can be varied by a factor of 1,000 by shifting the position of a movable clamp. Reprinted with permission from Proc. Natl. Acad Sci. USA, 84, July 1987, 4722. 

CUORICINO crystals are grouped in elementary modules of four elements (see Fig. 15.7) held between two copper frames joined by copper columns. PIPE pieces are inserted between the copper and TeOz, as a heat impedance and to clamp the crystals. There is a 6 mm gap between crystals with no material in between. The four detectors are mechanically coupled some of the PTFE blocks and springs act simultaneously on two crystals. 

Senti and Witnauer206 have reported studies on the fiber diagrams from various alkali-amyloses. Specimens were obtained by deacetylating clamped specimens of amylose acetate with the appropriate alkali. The positions of the alkali ions and the lateral packing of the amylose chains were determined with the aid of Patterson projections. In the A - and B -modifica-tions, the fiber period was 22.6 A. (extension of 6 D-glucose units), whilst in the V -modification it was 8.0 A. These authors have also studied in detail the addition compounds of amylose and inorganic salts with special reference to the structure of the potassium bromide-amylose compound.206 Oriented alkali fibers were treated with the appropriate salt solution. Stoichiometric compounds were formed. The x-ray patterns from these showed that the addition compounds with potassium salts crystallized in... 

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