The change rate of the

critical frequency between the unslotted brake pad and Sample 3 could be calculated from Table 7.

As the

critical frequency is lower than the switching frequency, it cannot be avoided that the

critical frequency is within the concerned range of the impedance spectroscopy.

Therefore it follows that the applicability of formula (2) is limited by the

critical frequency value, [f.sub.cr].

For such adaptivity, the

critical frequency [[omega].sub.ci] is online tuned to be the dominant modal frequency of the cable-damper system identified from the measured cable response [v.sub.d] with the employment of the HHT technique [28].

The

critical frequency [f.sub.cr]) occurs when the structural and acoustic wavelengths are equal to one another and is expressed as

Depending on the material and the stress level, the specimen surface temperature rise can be stabilized at a maximum frequency referred to as

critical frequency. At frequencies above the

critical frequency, temperature rise can continuously increase and the temperature in the material can even reach the melt point.

The peak value of electron density of [F.sub.2] layer is calculated with respect to measured ordinary

critical frequency as given in the expression, equation (3) postulated by Anderson and Matsushita in 1974 (Robert and Andrew, 2004; Barclay, 2003).

Suppose that the

critical frequency at the Earth's equator [f.sub.c0], calculated as [f.sup.2.sub.c0] = K x [N.sub.max] [being K = ([q.sup.2.sub.e]/[[epsilon].sub.0])/(4[[pi].sup.2][m.sub.e]) = 8.061382, [10.sup.-5] [MHz.sup.2] x [cm.sup.3]], can assume the following values: [f.sub.c0] = 3.65 MHz, [f.sub.c0] = 5.65 MHz, [f.sub.c0] = 6.85 MHz, [f.sub.c0] = 7.60 MHz, [f.sub.c0] = 7.80 MHz, [f.sub.c0] = 8.60 MHz, [f.sub.c0] = 9.15 MHz, and [f.sub.c0] = 10.45 MHz.

In another study, Zagatto and colleagues (27) with the objective of testing the validity of the

critical frequency model determined by using a specific protocol on table tennis, the researchers analyzed the aerobic (critf) and anaerobic (anaerobic work capacity--AWC) parameters of the model, the realization of two specific tests on table tennis and two on conventional ergometers were proposed.

(2008b) validated a

critical frequency specific test (critf) for estimating the aerobic endurance of table tennis players.

(2), it may be shown that, for normal incidence, the

critical frequency is given by

Perrone, "A local ionospheric model for forecasting the

critical frequency of the F2 layer during disturbed geomagnetic and ionospheric conditions," Annals of Geophysics, Vol.