This formula, however, tacitly supposes that the instanton period depends monotonically on its amplitude so that the zero-amplitude vibrations in the upside-down barrier possess the smallest possible period 2nla>. This is obvious for sufficiently nonpathological one-dimensional potentials, but in two dimensions this is not necessarily the case. Benderskii et al. [1993] have found that there are certain cases of strongly bent two-dimensional PES when the instanton period has a minimum at a finite amplitude. Therefore, the cross-over temperature, formally defined as the lowest temperature at which the instanton still exists, turns out to be higher than that predicted by (4.7). At 7 > Tc the trivial solution Q= Q Q is the saddle-point coordinate) emerges instead of instanton, the action equals S = pV (where F " is the barrier height at the saddle point) and the Arrhenius dependence k oc exp( — F ") holds. [Pg.61]

Though due to the fact that it is difficult to interprete amplitude dependence of the elastic modulus and to unreliable extrapolation to zero amplitude, the treatment of the data of dynamic measurements requires a special caution, nevertheless simplicity of dynamic measurements calls attention. Therefore it is important to find an adequate interpretation of the obtained results. Even if we think that we have managed to measure correctly the dependences G ( ) and G"( ), as we have spoken above, the treatment of a peculiar behavior of the G (to) dependence in the region of low frequencies (Fig. 5) as a yield stress is debatable. But since such an unusual behavior of dynamic functions is observed, a molecular mechanism corresponding to it must be established. [Pg.94]

Figure 1.10 (a) The dispersion mode line should have zero amplitude at resonance, (b) The deuterium lock keeps a constant ratio between the static magnetic field and the radiofrequency. This is achieved by a lock feedback loop, which keeps the frequency of the deuterium signal of the solvent unchanged throughout the experiment. [Pg.19]

Figure 1.11 The dispersion-mode line shape showing the zero amplitude at the center of the peak but nonzero amplitude on each side. |

There is a considerable literature [10-13] devoted to finding approximate formulas for the frequency of the simple pendulum for non-zero amplitudes, usually based on mathematical arguments designed to approximate elliptic functions. [Pg.114]

Note that the potential energy V(x) rises to infinite values at sufficiently large displacement. One should expect this boundary condition to mean that the vibrational wavefunction will fall to zero amplitude at large displacement (as in the square well case, but less abruptly). One should also expect that the confining potential well would lead to quantized solutions, as is indeed the case ... [Pg.112]

As the pressure increases further, a second HB point (HB2) appears at the extinction point E and shifts toward the other HB HBi) point. An example is shown for 4 atm in Fig. 26.1c. Ignition Ii is no longer oscillatory, because the stationary partially ignited branch becomes locally stable in the vicinity of /i. Time-dependent simulations indicate that the two HB points are supercritical, i.e., self-sustained oscillations die and emerge at these points with zero amplitude. In this case, the first extinction Ei defines again the actual extinction of the system. [Pg.429]

Note 3 The flexural modulus has been given the same symbol as the absolute modulus in uniaxial deformation as it becomes equal to that quantity in the limit of zero amplitudes of applied force and deformation. Under real experimental conditions it is often used as an approximation to i . ... [Pg.177]

There can be a solution with non-zero amplitude (that is, X / 0), only if u> is equal to F/m. The system can execute periodic motions only for a unique frequency. [Pg.56]

An eigenstate corresponds to a row vector with zero amplitude everywhere except at the base state function that is the case. It is then defined in Hilbert space and does not stand for an individual molecular state. The corresponding base state cannot be a dynamically unstable state as it is time independent. This is an important difference with standard approaches [15]. [Pg.180]

The access to different -regions is controlled by the vibration spectra. In particular, it is the anti-symmetric vibration mode that may shift the geometry towards the point of maximal mixing. The other way round, freezing this mode will trap the quantum system at the initial state, cis or trans as the case may be. Now, a vibration excitation along this anti-symmetric mode will be prompting the electronic activity of the system. For example, a perpendicular symmetric attack of carbene can only proceed if non-zero amplitude develops at the diradical states. This concept includes the elementary orbital considerations and overcome them. [Pg.190]

Further, ions are not hard, billiard ball like spheres. Since the wave functions that describe the electronic distribution in an atom or ion do not suddenly drop to zero amplitude at some particular radius, we must consider the surfaces of our supposedly spherical ions to be somewhat fuzzy. A more subtle complication is that the apparent radius of an ion increases (typically by some 6 pm for each increment) whenever the coordination number increases. Shannon10 has compiled a comprehensive set of ionic radii that take this into account. Selected Shannon-type ionic radii are given in Appendix F these are based on a radius for O2- of 140 pm for six coordination, which is close to the traditionally accepted value, whereas Shannon takes the reference value as 126 pm on the grounds that it gives more realistic ionic sizes. For most purposes, this distinction does not mat-... [Pg.84]

As the dimensionless concentration of the reactant decreases so that pi just passes through the upper Hopf bifurcation point pi in Fig. 3.8, so a stable limit cycle appears in the phase plane to surround what is now an unstable stationary state. Exactly at the bifurcation point, the limit cycle has zero size. The corresponding oscillations have zero amplitude but are born with a finite period. The limit cycle and the amplitude grow smoothly as pi is decreased. Just below the bifurcation, the oscillations are essentially sinusoidal. The amplitude continues to increase, as does the period, as pi decreases further, but eventually attains a maximum somewhere within the range pi% < pi < pi. As pi approaches the lower bifurcation point /zf from above, the oscillations decrease in size and period. The amplitude falls to zero at this lower bifurcation point, but the period remains non-zero. [Pg.76]

There are no unstable limit cycles in this model, and the oscillatory solution born at one bifurcation point exists over the whole range of stationary-state instability, disappearing again at the other Hopf bifurcation. Both bifurcations have the same character (stable limit cycle emerging from zero amplitude), although they are mirror images, and are called supercritical Hopf bifurcations. [Pg.77]

At the point of Hopf bifurcation, the emerging limit cycle has zero amplitude and an oscillatory period given by 2n/a>0. As we begin to move away from the bifurcation point the amplitude A and period T grow in a form we can calculate according to the formulae... [Pg.120]

When the Hopf bifurcation at p is supercritical (/ 2 < 0) the system has just a single stable limit cycle. This emerges at p and exists across the range p < p < p, within which it surrounds the unstable stationary-state solution. The limit cycle shrinks back to zero amplitude at the lower bifurcation point p%. This behaviour is qualitatively the same as that shown with the simplifying exponential approximation and is illustrated in Fig. 5.4(a). [Pg.125]

nodal plane or surface is the locus of all points at which a wave-function has zero amplitude as a result of its changing sign on passing from one side of the surface to the other the probability of finding an electron on such a surface is zero. o-Bonds and o-orbitaJs are defined as those having no nodal surface which contains the bond axis such bonds and orbitals will be symmetric about the bond axis. In this section we consider which AOs of a central atom A (which is bonded to a set of other atoms) can be combined to form a hybrid orbital which is symmetric about the bond axis and therefore capable of cr-bonding. [Pg.225]

In the 1/1 entrainment region each side of the resonance horn terminates at points C and D respectively. These points are codimension-two bifurcations and correspond to double +1 multipliers. As the saddle-node curve at the right horn boundary rises from zero amplitude towards point D, one multiplier remains at unity (the criterion for a saddle-node bifurcation) as the other free-multiplier of the saddle-node increases until it is also equal to unity upon arrival at point D. The same thing occurs for the left boundary of the resonance horn. The arc CD is also a saddle-node bifurcation curve but is different from those on the sides of the resonance horn. As arc CD is crossed from below, the period 1 saddle combines not with its companion stable node, but with the unstable node that was in the centre of the phase locked torus. As the pair collides, the invariant circle is lost and only the stable node remains. Exactly the same scenario is observed for the 1/2 resonance horn as well. [Pg.317]

When the HSS solution of the chemical rate equations (la)—(lc) first becomes unstable as the distance from equilibrium is increased (by decreasing P, for example), the simplest oscillatory instability which can occur corresponds mathematically to a Hopf bifurcation. In Fig. 1 the line DCE is defined by such points of bifurcation, which separate regions of stability (I,IV) of the HSS from regions of instability (II,III). Along section a--a, for example, the HSS becomes unstable at point a. Beyond this bifurcation point, nearly sinusoidal bulk oscillations (QHO, Fig. 3a) increase continuously from zero amplitude, eventually becoming nonlin-... [Pg.207]

In the stripe-like inhomogeneity shown in Fig. 1 (where the stripes are directed in the y-direction), one has (x , y ) = (4am, an), where m and n are integers, and thus p]( k ) creates a state with non-zero amplitudes in the even n points, while pt( kp) creates a state with non-zero amplitudes in the odd n points. A similar result would be obtained also in lattice areas where the stripes are... [Pg.193]

© 2019 chempedia.info