Alternative frequencies

Some induction heating furnaces must operate at frequencies higher than the supply frequency. Formerly, rotating motor alternator frequency converters were used. Now the avadabdity of high speed, high power sdicon controlled rectifiers for use in frequency converters has made rotary converters obsolete. Modem units operate at higher efficiency, cost less, require less factory space, and coordinate readdy with process controls (2). 

For routine studies with the ESR spectrometer, it is most convenient to work at X-band frequencies ( 9.5 MHz or 3 cm). The sample is usually contained in a 4 or 5 mm diameter quartz tube having a sensitive region about 2 cm in length. An alternative frequency is at Q-band ( 35,000 MHz or 1 cm). Here, the cavity dimensions are much smaller and the diameter of the sample tube is less than 2 mm. This creates some problems in handling and degassing powder samples. By varying the frequency it is possible to determine which features in a spectrum are due to Zeeman interactions... 

Boyd (1959) has carried out an extensive dielectric investigation of 6-6 Nylon using alternating frequencies from 50 to 7 x 107 cps and covering the temperature range —40 to 100° C. The a peak was found to occur at 50° C at 10 cps and at 72° at 103 cps. The lower the frequency the lower the temperature of the peak. In quenched 6-6 Nylon Wilhoit and Dole (1953) found an indication of a glass transition from about 40 to 50° C. 

Acoustic waves. The microbalance is generally based on quartz crystals which are mechanically distorted when subjected to an electrical potential. The source is usually an alternating frequency in the MHz region and will be perturbed by minor changes at... 

The vibrational analysis of the electronic transitions affords the vibrational frequencies listed in Table 23 force constants have not yet been calculated. The SiH (SiD) stretching frequencies v are quite uncertain, and the alternative frequencies near 1750 cm 1 appear to be more probable by evidence of the SiH shortening upon electronic excitation and by comparison with SiH2 ( Ai, r0 1.5163 A, j>siH 2030 cm 1). Of course, /o(SiH) has been determined only for HSiCl/DSiCl, but has been transferred to HSiBr and HSil. 

The key limiting factor is the penetration depth of microwave irradiation, which is only a few centimeters in most solvents at 2.45 GHz. An issue therefore arises in getting sufficient microwave power into the reaction mixture to achieve the desired heating effect. The core of a large reactor vessel will not receive any microwave radiation as it will all have been absorbed by the outer layers. As a result, the center is effectively conductively or convectively heated, and the potential benefits of microwave heating will be lost. Penetration depth does, however, vary with frequency. Only a limited number of Industrial, Scientific, and Medical (ISM) frequencies are allowed so as not to interfere with military and civil aviation frequencies and telecommunications. Alternative frequencies are used for other large-scale applications and thus may provide an alternative solution to the scale-up of micro-wave chemistry. ... 

MAX/MIN A display mode on some spectrum analyzers that shows the maximum and minimum signal levels at alternate frequency points, its advantage is its resemblance to an analog display. 

An alternative frequency-dependent viscosity, which could also be called the dynamic viscosity, is the absolute value t = (t) -1- - (G - -... 

Result It is shown that although the model can illustrate the effects of electric and magnetic loading magnitude alterations and various electric durations, it cannot respond appropriately to the alternating frequencies of sinusoidal waveform. 

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