Signal cancellation mechanisms

All polyamides are suitable for being hydrolyzed in proportion of their water content. Depending on the relative orientation of the dipoles formed by amide functional groups, PA may or may not exhibit piezoelectric properties, i.e., generation of an electric signal under mechanical constraint. PAs that have all their dipoles directed in same direction (PA-7, PA-9, etc.) leads to a marked piezoelectric effect whereas the alternation of orientations (in PA-6 for instance) cancels this effect. 

Multisizer 4). The principle of the symmetric dual-channel design is to have the noise levels for the output signals (Vdi and Vd2 as indicated in Fig. 3) in both gate branches identical, and hence, the noises can be canceled by using a differential amplification mechanism. However, ideal noise subtraction is not possible due to the real-world limitation in fabricating identical dual channels. Furthermore, this dual-channel method will not be able to detect particles when two particles pass the two apertures at the same time because the two signals with the similar amplitude will be subtracted by each other and canceled at the second stage of the differential amplifier. 

From this point of view, nitrogen-15 exhibits a peculiarity which is characteristic of nuclei with a negative gyromagnetic ratio and is frequently emphasized. Indeed, it is possible for the relative contribution of the dipolar mechanism to be reduced to about 20% and therefore to give values of n = -1 and I/Io = 0. The signal is then cancelled by the Overhauser effect. This phenomenon should be kept in mind, in particular, when using relaxation reagents, since the electronuclear interaction may compete with the nuclear dipolar effect to yield approx-imatively n j g = 1 [Eq. (2.6)] (H 13). 

In order to achieve equal lift on the advancing and retreating side of the rotor in spite of the unsymmetric flow velocity distribution, the common helicopter concept makes use of a varying angle of attack. This is introduced with the necessary cycle duration of one revolution by the swash plate mechanism. The idea is to actively control the blade pitch, and cancel or reduce the appearing vibrations by superposition of an adequate signal. 

As most of the characteristic perturbations occur with the blade passage frequency and its higher harmonics, the simplest approach is to employ such signals to achieve cancellation. With sensors at relevant points of the airframe, the vibratory load factors are measured and then processed by a control system. The necessary motion is produced by stationary hydraulic actuators, inducing a vertical displacement of the swash plate and thus a collective actuation of the blades. Such an actuation mechanism may also modify the inclination of the swash plate, but it still is not possible to respond to events at an individual blade. 

Hence for practical concentration measurements, (Jj must be reduced to a minimum in order to maximize the validity range of Lambert-Beer s law. With optical or x-ray extinction measurements, this is achieved by reducing the receiver s aperture angle but it appears to be difficult to reduce Pj below about Pj = 10". 10". With piezoelectric ultrasonic receivers however, pj is extremely low, since the electric output from the receiver is proportional to the integral of all mechanical stresses over the sensor volume. Hence, upon incidence on a plane piezoelectric receiver, only a plane wave can produce a significant signal, whereas the stresses produced by scattered or multiply scattered waves will cancel out statistically, see Fig. 5. 

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