Untwisting

In false twist texturing (FTT), shown schematically in Figure 7, a device twists yam upstream of its location as the threadline passes across a heater, and the yam untwists downstream from the device and is wound up. If the yam is not heated downstream from the twist device, it has bulk and high elasticity (stretch). If the yam is heated downstream from the twist device, it has bulk, but much less stretch. FTT machines initially used two steps to sequentially draw and texture. Later machines combined those steps to simultaneously draw and texture (92). Initial machines used pin spindles as the false twist device. Texturing speeds were about 150 m/min and slowly increased to about 300 m/min. As POY quaUty and stmctural stabiUty improved, new... 

Bundle of continuous, untwisted glass fibers. Glass fibers are wound onto a roll called a roving package. ... 

Alifdocken, v.t. wind up, roll up bundle, shock. (Ulfdfirren, v.t. dry, desiccate, anfdrkngen, v.t. press open force upon, anldrehen, v.t. screw open, untwist turn on (as gas) turnup (Ceram.) throw. 

Improper seizing that.allow s. slack fpm orte. ot more strands tb Wotk back into. rape irhpfopaf, method of socketing or poor wCrkmanship in socketing frequently shown by rope being. untwisted at socket, loose or drawn. ... 

Flexible hose must not be twisted during installation. This will reduce the life of the hose and may cause the fittings to loosen. You can determine whether a hose is twisted by looking at the layline that runs along the length of the hose. If the layline does not spiral around the hose, the hose is not twisted. If the layline does spiral around the hose, the hose is twisted and must be untwisted. Flexible... 

This presented a more difficult problem How do the double-helical strands separate during DNA synthesis In a rapidly growing cell such as E. coli it has been calculated that if the strands separate by untwisting, the molecule would have to rotate at 10,000 rpm, a rate that is highly improbable. The answer to this problem lies in an understanding of the mechanism of DNA replication at the enzyme level. We will return to this subject after first considering the enzymes involved in DNA synthesis. 

Armed with this information, the unwinding problem mentioned ear-lier can be reconsidered. By the alternating action of endonucleolytic and ligase activities, the unwinding of DNA could be reduced to an untwisting of only a small part of the double helix at any given time. Both activities are part of the enzyme called topo-isomerase 1. 

Figure 4.76 Side and end views of the 90°-twisted ethylene complex (0.5 kcal mol-1 above the untwisted equilibrium complex, Fig. 4.74(b)), showing the interaction of the unsymmetric pi bond with Ti.

In conclusion, the pBR nucleosome differs from the 5S nucleosome in two main respects its 1-bp untwisting at each of SHL 5 and —5, and its easy access to the positive conformation, which may result from a slight reorientation of entry/exit DNAs (see above). Importantly, these two features are necessarily related, at least statistically, because, as previously mentioned, each nucleosome represents an average of individual nucleosomes which differ from one another in a number of criteria, in addition to their twist (see below). Our model [29] proposed that reorientation is mediated by these local untwistings, which act at a distance to modify the interactions of H3 N-terminal tails with entry/exit DNAs at SHL 7 (Fig. 1(b)) and, perhaps, also further along them, through the rotation they inflict to the distal DNA stretches between SHL 5 to 7 and —5 to —7. 

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