ABSTRACT
We present a general study of oscillations in suspended one-dimensional elastic systems clamped at each end, exploring a wide range of slack (excess length) and downward external forces. Our results apply directly to recent experiments in nanotube and silicon nanowire oscillators. We find the behavior to simplify in three well-defined regimes which we present in a dimensionless phase diagram. The frequencies of vibration of such systems are found to be extremely sensitive to slack.
Subject(s)
Energy Transfer , Models, Chemical , Nanotechnology/methods , Nanotubes, Carbon/analysis , Nanotubes, Carbon/chemistry , Oscillometry/methods , Computer Simulation , Elasticity , Materials Testing/methods , Molecular Conformation , Nanotubes, Carbon/ultrastructure , Stress, MechanicalABSTRACT
This Letter introduces an ab initio study of the full activation-volume tensor of crystalline defects as a means to make contact with mechanical response experiments. We present a theoretical framework for the prediction of the internal friction associated with divacancy defects and give the first ab initio value for this quantity in silicon. Finally, making a connection with defect alignment studies, we give the first unambiguous resolution of the debate surrounding ab initio verification of the ground-state structure of the defect.
ABSTRACT
We show that modes of axially uniform waveguides of arbitrary cross section can be made to have anomalous dispersion relations resulting from strong repulsion between two modes. When the axial wave vector k is 0, the two modes have different TE/TM symmetry and thus can be brought arbitrarily close to an accidental frequency degeneracy. For nonzero k, the symmetry is broken causing the modes to repel. When the modes are sufficiently close together this repulsion leads to unusual features such as extremely flattened dispersion relations, backward waves, zero group velocity for nonzero k, atypical divergence of the density of states, and nonzero group velocity at k=0.
