Modes, standing waves

Figure Cl.4.5. Population modulation as the atom moves through the standing wave in the Tin-periD-lin one dimensional optical molasses. The population lags the light shift such that kinetic is converted to potential energy then dissipated into the empty modes of the radiation field by spontaneous emission (after 1171).

We have already seen (p. 2) that the individual electrons of an atom can be symbolised by wave functions, and some physical analogy can be drawn between the behaviour of such a wave-like electron and the standing waves that can be generated in a string fastened at both ends—the electron in a (one-dimensional) box analogy. The first three possible modes of vibration will thus be (Fig. 12.1) ... 

Let us consider thermal radiation in a certain cavity at a temperature T. By the term thermal radiation we mean that the radiation field is in thermal equilibrium with its surroundings, the power absorbed by the cavity walls, Fa (v), being equal to the emitted power, Pe v), for all the frequencies v. Under this condition, the superposition of the different electromagnetic waves in the cavity results in standing waves, as required by the stationary radiation field configuration. These standing waves are called cavity modes. 

Different axial modes (optical standing waves) can be set up in a cavity of length L provided that the frequency v fulfills the condition... 

Fig. 13.21 shows another example of oscillatory burning of an RDX-AP composite propellant containing 0.40% A1 particles. The combustion pressure chosen for the burning was 4.5 MPa. The DC component trace indicates that the onset of the instability is 0.31 s after ignition, and that the instability lasts for 0.67 s. The pressure instability then suddenly ceases and the pressure returns to the designed pressure of 4.5 MPa. Close examination of the anomalous bandpass-filtered pressure traces reveals that the excited frequencies in the circular port are between 10 kHz and 30 kHz. The AC components below 10 kHz and above 30 kHz are not excited, as shown in Fig. 13.21. The frequency spectrum of the observed combustion instability is shown in Fig. 13.22. Here, the calculated frequency of the standing waves in the rocket motor is shown as a function of the inner diameter of the port and frequency. The sonic speed is assumed to be 1000 m s and I = 0.25 m. The most excited frequency is 25 kHz, followed by 18 kHz and 32 kHz. When the observed frequencies are compared with the calculated acoustic frequencies shown in Fig. 13.23, the dominant frequency is seen to be that of the first radial mode, with possible inclusion of the second and third tangential modes. The increased DC pressure between 0.31 s and 0.67 s is considered to be caused by a velocity-coupled oscillatory combustion. Such a velocity-coupled oscillation tends to induce erosive burning along the port surface. The maximum amplitude of the AC component pressure is 3.67 MPa between 20 kHz and 30 kHz. - ...

The lowest frequency standing wave has no node (t/ ) and is called the fundamental5 (frequency). Higher frequency modes are harmonics5 which have increasing numbers of nodes. 

Figure 7.14 Principles of mode-locking, (a) Standing waves in a cavity of length L defined by two mirrors mp, m2, (b) Selection of frequencies within the emission spectrum of the lasing material v is the frequency...

The wavefunctions of the normal scattering modes are the standing waves produced by a linear combination of incoming coulomb wavefunctions which is reflected from the ionic core with only a phase shift. The composition of the linear combination is not altered by scattering from the ionic core. These normal modes are usually called the a channels, and have wavefunctions in the region rc[Pg.418]

There are two modes excited by the AC field, longitudinal and transverse. For crystals in the 100-300 pm thickness range, only the transverse standing wave needs to be considered (Janshoff et al 2000). The actual lateral displacement of a point on the crystal surface (and therefore the mass sensitivity) is the Gaussian function of the radial distance from the center of the electrode (Fig. 4.5). It also depends on the amplitude of the applied electric field and ranges from few nm/V in water to tens of nm/V in air or in vacuum. 

Fig. 5. 33 Fields in a microwave resonance dielectric in the simplest standing wave mode (a) magnetic field (b) electric field (c) variation in Ev and Ez with r at z — 0, with reference to cylindrical coordinates (the z axis is perpendicular to the plane of the disc and the origin is at the disc centre).

S-NDR systems (4DL inhibitor Turing-like structures (n > 1) standing waves, anti-phase oscillations with n = 1 or mixed-mode structures with n > 1 pulses stationary domains (n = 1 or n > 1)... 

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