Torsional coupling

Very low-frequency vibrations have been observed in proteins (e.g., Brown et al., 1972 Genzel et al., 1976), which must involve concerted motion of rather large portions of the structure. By choosing a suitable set of proteins to measure (preferably in solution), it should be possible to decide approximately what structural modes are involved. Candidates include helix torsion, coupled changes of peptide orientation in /3 strands, and perhaps relative motions of entire domains or subunits. These hypotheses should be tested, because the low-frequency vibrations probably reflect large-scale structural properties that would be very useful to know. 

Double-crossover molecules have been used extensively to characterize the properties of Holliday junctions. The strong torsional coupling between their crossover points has been exploited to construct symmetric immobile junctions (S. Zhang et al. 1993), junctions in which one of the crossovers is flanked by homology, but is nevertheless unable to branch migrate. Symmetric immobile junctions have been used to characterize crossover isomerization thermodynamics (S. Zhang and Seeman 1994) and, more recently, the sequence dependence of the branch point stability (W. Sun et al., 1998). Double crossover molecules have also been employed to establish the cleavage patterns of endonuclease VII, an enzyme that resolves branched junctions (Fu et al. 1994 a). 

Typical of this class of viscometer is the coaxial or Couette type of instrument described in Volume l, Section 3.7.4. The sample fluid is contained within the annular space between two coaxial cylinders, either of which may be rotated by a motor with the remaining cylinder suspended elastically in such a way that the torsional couple exerted on the latter can be measured. If the outer cylinder of radius r2 rotates with an angular velocity cou and the inner cylinder of radius r, is stationary, and the torque (or viscous drag) per unit length of cylinder exerted on the inner cylinder is T, then, for a Newtonian fluid(49) ... 

Besides the oblique contact, tangential displacements may also be produced in the contact of two elastic spheres under the actions of a compressional twist, as shown in Fig. 2.13. Since the torsional couple does not give rise to a displacement in the z-direction, the pressure distribution is not influenced by the twist and is thus given by the Hertzian contact theory. 

If a torsional couple or twist moment Mz were applied to the two spheres in contact, the contact surface would undergo a rigid rotation relative to distant points in each body if there were no-slip motion at the interface. In this case, the tangential displacements could be expressed by... 

P(3) Laminates that are subject to bending-stretching-torsion coupling are defined as generally orthotropic. Typically, generally orthotropic laminates have a symmetrical and balanced stacking sequence of plies, with an appreciable amount (more than about 20%) of reinforcement orientated at other than 0° and 90° (e.g. +45° or -45°). 

P(4) Specially orthotropic laminates are those with uncoupled in plane and flexural behaviour and that do not exhibit bending stretching torsion coupling. Normally this is reached with a laminate structure that consists of 0° and/or 90° plies only. 

P(2) The design of certain members (e.g. in which appreciable bendingstretching-torsion coupling, or some combination of these, occurs) is outside the scope of the EUROCOMP Design Code. Reference should be made to the specialist literature or design programmes (see Chapter 4) for information and recommendations on the anniications anaivsis and... 

Fig. 5. Time evolution of the population probability of the upper (5i) adiabatic electronic state of the photoisomerization model with (a) two degrees of freedom (torsion, coupling mode), (b) three degrees of freedom (torsion, coupling mode, tuning mode), and (c) four degrees of freedom (torsion, coupling mode, two tuning modes).

Furthermore, we suppose that the bending-torsion coupling and the axial vibration of the beam centerline are negligible and that the components of the displacement field u of the beam are based on the Timoshenko beam theory which, in turn, means that the axial displacement is proportional to z and to the rotation ir x, t) of the beam cross section about the positive y-axis and that the transverse displacement is equal to... 

Kan, C.L. Chopra, A.K. 1977. Effect of torsional coupling on earthquake forces in buildings. Journal of Structural Division ASCE 103(4) 805-819. 

Bernhard, A.P.F. and Chopra, I. Analysis of a bending-torsion coupled actuator for a smart rotor with active blade tips. Smart Mater. Struct., 10 (2001), pp. 35-52... 

Ueng, J. M., Lin, C. C., Wang, J. F. (2008). Practical design issues of tuned mass dampers for torsionally-coupled buildings under earthquake loadings. Structural Design of Tall and Special Buildings, 77(3), 133-165. doi 10.1002/tal.336... 

Torsionally Coupled (TC) Effect An effect that describes the coupling of translation and torsion of a building due to the inconsistency of the center of rigidity and the center of mass. 

In a study of methyl-substituted pyridines, the aryl regions of the overtones show a simplified structure having one peak progression for each nonequivalent C-H. The methyl regions of the methylpyridines show complex profiles. The band profile in 3- and 4-methylpyridine is similar to that of toluene because the methyl groups of these compounds are free rotors, and all have a low-energy barrier to rotation. However, the methyl band profiles of 2-methylpyridine are complex, and these patterns indicate that vibration-torsional coupling is an important contribntor to the complex structure." ... 

This work proposes a new method for the inclusion of coupling between a torsional mode and other degrees of freedom in a valid statistical model of a moleeule. While totally separable approximations like the HO-RR method are quite often useful, they should be used cautiously in quantitative work. The semiclassical adiabatic method developed here accounts for torsional coupling while circumventing the necessity for repeated quantum determinations of torsional eigenenergies at all levels in internal excitation of the molecule. Since the torsional motion is typically of low frequency, this semiclassical approximation is generally good. 

D Bermejo, J Santos, P Cancio, JM Fernandez, S Montero. Vibrational-torsional coupling. High-resolution stimulated Raman spectrum of the V3 band of ethane ( C2H6). J Chem Phys 97 7055-7063, 1992. 

These subtle geometry changes are of little consequence to the overall conformation of an oligosaccharide in. solution, except in so far as they may lead to more or less puckered pyranoid rings. In biomolecular force fields this bond-torsion coupling may be reproduced crudely by employing... 

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