Angle of twist

Torsional Stiffness (Torsion Constant). Torsional stiffness of a body is appHed torque (N-m) divided by angle of twist (rad). Its SI unit is N-m/rad. 

Angle of twist The azimuth change through which the drillstring must be turned to offset the twist caused by the reactive torque of the downhole motor. 

Shear stress-strain data can be generated by twisting (applying torque) a material specimen at a specified rate while measuring the angle of twist between the ends of the specimen and the torque load exerted by the specimen on the testing machine. Maximum shear stress at the surface of the specimen can be computed from the measured torque that is the maximum shear strain from the measured angle of twist. 

Certain materials may be weak in shear, and for these it is appropriate to measure their strength by torsion tests. For such tests, the material is fabricated into a rod of circular cross-section, and twisted about its longitudinal axis. The angle of twist is proportional to the shearing strain, and the... 

Figure 9.4. Potential energy diagram for stilbene as a function of angle of twist. (From Ref. 22.)...

Figure 9.2. The energies of the ground A state and electronically excited states shown as a function of 6, the angle of twist. (O) Singlet states ( ) triplet states. The G and H curves represent two states that nearly coincide. (From Ref. 3.)...

The relaxed nonvertical excited state is referred to as the p-state as it has adjacent p-orbitals which are orthogonal due to a 90° angle of twist from the geometry of the vertical excited state. Figure 8.1 shows that the same p-state is produced from both geometrical isomers, and similarly, rapid radiationless decay of this p-state can produce either the cis or the trans isomer. 

In several examples including nitroanilines, the effect of twisting the chromophore from planarity decreases the absorption intensities. The reasons for the bathochromic effect as the angles of twist in the 4-aniline series increase is subject to discussion. When considering this (as well as in all attempts to obtain definitions of polarity of solvents by quantitative parameters) it is important to exclude or minimize the presence of hydrogen bonding overlapping158 other interactions. 

The twist is almost universally constant in pitch, although older weapons with an increasing twist may be encountered occasionally. In the Latter case — provided the rifling continues to grip the envelope thruout the bullet travel in the bore — the final angle of twist decides the rate of rotation... 

In a pyrrole derivative containing the molecular residue 5, X-ray analysis shows (85JCS(P1)899) that the formyl group is substantially coplanar with the heterocyclic ring (angle of twist 2.6°) and in the N(H),0-traws orientation. 

Those molecules which change their geometry in the excited state show a variation in their potential energy function with the angle of twist. Such variation for a single and a double bonded system is given in Figure 4.20. 

Fig. 27. A schematic plot of electronic energy versus angle of twist (about the double bond) in unsubstituted stilbene.

The directors (long molecular axes) of the constituent molecules in nematic phases are parallel to one another on average. This is the only order present in nematic liquid crystals, which are the most fluid type of liquid-crystalline phase. Molecules that form cholesteric phases must be optically active or contain an optically active dopant. As the phase name implies, the constituent molecules are frequently steroids and most commonly are cholesteric esters or halides. A conceptual model of the cholesteric phase includes layers of molecules in nematic-like positions, each layer being twisted slightly with respect to the ones above and below it. When the phase consists only of optically active molecules, the angle of twist between layers is typically less than one degree. Several subclasses of discotic phases exist. In all, the molecular planes of the constituent molecules are parallel. However, the discs can pack in nematic-like arrangements (ND) or in columns that are internally ordered (D ) or disordered (Dd) and may be stacked vertically,... 

Rotational and translational movements of bases. In considering the conformational flexibility of a polynucleotide it is useful to define the parameters associated with movement of base pairs or individual bases. The possible movements are indicated in Fig. 5-15 and in Table 5-3. A long axis is established for each base pair in a structure for which X-ray data are available. Making use of these axes, we can move along the helix and measure the angle of twist from one base pair to the next.142-145 While the mean value... 

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