Carrier wave

In the presence of weak disorder, one should consider an additional contribution to the resistivity due to weak localisation resulting from quantum interference effects and/or that due to Coulomb interaction effects. A single-carrier weak localisation effect is produced by constructive quantum interference between elastically back-scattered partial-carrier-waves, while disorder attenuates the screening between charge carriers, thus increasing their Coulomb interaction. So, both effects are enhanced in the presence of weak disorder, or, in other words, by defect scattering. This was previously discussed for the case of carbons and graphites [7]. 

In order to conveniently detect and display the resonance signal, audio modulation coils are used to modulate the static magnetic field. Close to a resonance the rf voltage will be audio amplitude modulated in the same way that a carrier wave is audio amplitude modulated in radio broadcasting. In this way by modulating with an amplitude large compared to the line width, the entire resonance signal may be displayed on a cathode-ray oscilloscope. 

The re arch in catalysis is still one of the driving forces for interface science. One can certainly add to the topics of interface physics the whole new field of interface problems that is about to spring out of the new high Tc superconducting ceramics, i.e. the fundamental problem of the matching of the superconducting carriers wave-functions with the normal state metal or semiconductor electron states, the super-conductor-superconductor interfaces and so on, as well as the wide open discovery field for devices and applications. 

In many telemetry systems the PCM signal is frequency modulated on to a carrier wave. This is termed frequency shift keying (FSK). In other arrangements, the output of the transducer is converted into fixed step changes of the phase of the modulating signal. A device for this purpose is termed a modulator/demodulator or modem. 

Microwave switches are beam-breaker-type point sensors with an accuracy of 13 mm (0.5 in.) and with pressure and temperature ratings up to 28 bar (400 psig) and 300°C (600°F). Pulse-type radar gauges have ranges up to 200 m (650 ft) and are accurate to 0.5% FS, whereas frequency-modulated carrier wave (FMCW) units have errors from 1 to 3 mm (0.04-0.125 in.). Their pressure and temperature ratings are up to 80 bar (1,200 psig) and up to 400°C (750°F). 

Frequency modulated carrier wave (FMCW) radar transmitters. (Courtesy of Thermo Measure Tech Inc.)... 

Radar level transmitters and gauges use electromagnetic waves, typically in the microwave bands to make a continuous liquid and some solid level measurements. The radar sensor is mounted on the top of the vessel and is aimed down, perpendicular to the liquid surface. Most tank-farm gauges are operated on the FMCW principle (Figure 3.121). Other gauges and transmitters, particularly the lowest-cost units, are operated on the pulse principle. Both principles are fundamentally based on the time of flight from the sensor to the level of the surface to be measured. In the FMCW method, this time of flight is tracked on a carrier wave in the pulse method, it is the echo return. 

Figure 2. Comparison of (A) lr Cd from freshly isolated chick cerebral hemispheres exposed to a weak radiofrequency field (147 MHz, 0.8 mW/cm2), amplitude-modulated at low frequencies, and (B) 45C2 efflux changes from exposure to far weaker electric fields (56 V/m) in the same frequency spectrum from 1 to 32 Hz. The peak magnitude of the efflux change is similar for the two fields, but opposite in direction. For the radiofrequency field (A), the unmodulated carrier wave U had no effect when compared with controls C. Field gradients differ by about six orders of magnitude between (A) and (B) (22, 23).

These results led us to analyze the relationship between carrier-wave frequency and power density. We developed a mathematical model (6) which takes into account the changes in complex permittivity of brain tissue with frequency. This model predicted that a given electric-field intensity within a brain-tissue sample occurred at different exposure levels for 50-, 147-, and 450-MHz radiation. Using the calculated electric-field intensities in the sample as the independent variable, the model demonstrated that the RF-induced calcium-ion efflux results at one carrier frequency corresponded to those at the other frequencies for both positive and negative findings. In this paper, we present two additional experiments using 147-MHz radiation which further test both negative and positive predictions of this model. 

Values of P. used in previously reported experiments on calcium- ion efflux from chick-brain samples at carrier-wave frequencies of 50, 147, and 450 MHz. 

Specific values of P. used in previously reported experiments on calcium-ion efflux from chick-brain samples are listed in Table I under the carrier wave frequency used in the experiment (3,4,1 ). In addition, values of P. which result in the same E in the sample have been calculated for the other carrier frequencies using Equations (3) and (4). For example, 3.64 mW/cm2 at 50 MHz, 0.83 mW/cm2 at 147 MHz, and... 

The relationship between effective power densities at different carrier frequencies can be viewed in a different manner by plotting carrier frequency versus incident power density (Figure 3). Lines connecting P. values which produce the same internal electric field intensity at 50, 147, and 450 MHz are as shown. This figure serves to illustrate the smaller range of values as carrier-wave frequency is increased from... 

In other experiments,+ he effect of temperature has been determined by measuring Ca efflux from chick brain tissue incubated at 32°C and 4l°C (3). When compared to 37°C, the efflux was 9% lower at 32°C and 15% higher at 4l°C. The temperature difference in control and irradiated samples could be experimentally controlled to less than 1°C, therefore temperature variation in the samples do not account for the 15-24% change in Ca efflux caused by exposure to 16 Hz modulated carrier waves. 

The external field E ) is a modulated carrier wave represented by... 

The first term in Equation (11) is the unmodulated carrier wave, of amplitude kjE, and the second term is a signal at the modulation frequency, of amplitude k2E2 m, generated by the nonlinear dependence of E on E. oc... 

The field intensities, or wave amplitudes, that have produced changes in calcium-ion efflux at typical carrier frequencies and at typical modulation frequencies may be used to estimate the amount of nonlinearity that would be required to conform with observed results. Adey (1 1) has reported that a relatively small internal electric field intensity, on the order of 10"7 V/cm, at 16 Hz is sufficient to alter the binding of calcium ions in brain tissue. The internal field intensity of the carrier waves shown in Table 1 are on the order of 10-2 V/cm. From these observations, the ratio of the amplitudes of the first two terms in Equation (11) is... 

Keeping the average electric field intensity the same within a spherical model of chick-brain in buffer solution at different incident carrier wave frequencies requires that incident power density be changed with frequency to compensate for the change in complex permittivity and wavelength with frequency. The resulting Equations (3) and (A) relate corresponding values of P. at carrier frequencies of 50, 1A7, and A50 MHz. 1... 

The specific carrier-wave amplitudes (field intensities) which have been found to be effective in producing Ca ion efflux are discussed in terms of tissue properties and relevant mechanisms. The brain tissue is hypothesized to be electrically nonlinear at specific field intensities this nonlinearity demodulates the carrier and releases a 16 Hz signal within ljie tissue. The 16 Hz signal is selectively coupled to the Ca ions by some mechanism, perhaps a dipolar-typ +(Maxwell-Wagner) relaxation, which enhances the efflux of Ca ions. The hypothesis that brain tissue exhibits a slight nonlinearity for certain values of applied RF electric field intensity is not testable by conventional measurements of e because changes... 

To obtain envelope equations, one expresses the field in terms of an envelope by factoring out the carrier wave at a chosen reference angular frequency wr with the corresponding wave-vector Air = A1(0,0,wr) ... 

A strict derivation of the comb properties is not feasible as it depends on the special dispersion characteristics of the laser cavity and these data are not accessible with the desired degree of accuracy. Instead we only assume that the laser emits a stable coherent pulse train without any detailed consideration of how this is possible. Further we assume that the electric field E(t), measured for example at the output coupler, can be written as the product of a periodic envelope function A ) and a carrier wave C(t) ... 

Up to the scaling factors An this sum represents a periodic spectrum in frequency space. If the spectral width of the carrier wave Au>c is much smaller than the mode separation ojr, Eqn. 7 represents a regularly spaced comb of laser modes with identical spectral line shapes, namely the line shape of C(u>) (see Fig. 1). If C(oS) is centered at say uic then the comb is shifted from containing only exact harmonics of u)r by uic. The center frequencies of the mode members are calculated from the mode number n [23,24,21] ... 

On the other hand, there are measurements in which signal and noise cannot be directly filtered and the signal has to be transposed onto a carrier wave to be shifted away from the noise frequencies (modulation). Then an amplifier is tuned to the frequency of the carrier wave and the amplified original signal is finally recovered (demodulation). The use of a chopper in optical spectrophotometers is a common example of this process [i]. Ref [i] Horowitz P, Hill W (2001) The art of electronics. Cambridge University Press, Cambridge... 

An alternative method for excitation of nuclei over a range of chemical shifts is by irradiation with a weak, noise-modulated radio-frequency, instead of with strong r.f. pulses. In one realization of this method, protons were irradiated with repetitive sequences of noise that was truly random,162 and, in another,163 fluorine nuclei were excited by pseudo-random noise generated by amplitude modulation of the r.f. with maximum-length sequences of pulses from a computer or shift register (a series of flip-flop devices connected by feedback loops). With the carrier wave suppressed, the latter process is equivalent to phase modulation of the r.f. by+7r/2 radians when the pulse is turned on, and by —ir/2 radians when it is turned off. This method is identical with that used in most broadband, heteronuclear, noise decouplers, except that greater power is required for decoupling. 

Nuclear magnetic resonance (NMR) is a similar type of paramagnetic phenomenon. Like ESR, NMR involves the generation of a signal by the application of an external magnetic field, except that in NMR, shifts in the orientation of the nucleus, rather than of the unpaired electrons, are measured with respect to the external field (cf. Dyer 1965). The major point for our discussion, which would indicate that ESR rather than NMR would function as the modulated carrier-wave, is that unpaired electrons are characteristic of charge-transfer reactions and semiconduction, and as we have seen previously, serotonin and many of its analogs can function as power-... 

The first one is, through what mechanism could the organism detect the modulated carrier-wave Second, what sort of information could be carried by the wave ... 

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