Accuracy amplitude measurements

The method employed to obtain the results in this series of experiments was basically the same as that carried out previously by Key (1965a) who studied the effect of LSD-25 on the amplitude of individually evoked potentials in the cochlear nucleus. In the present study EPs were recorded in the LL and AC and averaged potentials evoked from consecutive tonal pips were analysed in preference to individual responses. This increased the accuracy of amplitude measurements by increasing the signal to noise ratio, but as the fluctuation in amplitude of EPs was also to be studied only a small averaging sample of 4 was chosen. 

The error Aviv in the determination reflects the accuracy of measurement of the vibration frequency (see. Fig. III.7, curve 2). Normally, the vibration frequency is fixed by the generator, and these vibrations are reproduced by the dust-covered surface. The error Ayly reflects the accuracy of measurement of the vibration amplitude. In our experiments, the combined error Av/v + Ayly was never greater than 5%. Hence, as with the centrifuging technique, the principal error here can be attributed to particle size variation. 

The error A u /u in the determination is associated with the accuracy of measuring the vibration frequency (see Fig. II.9). Usually, the frequency of vibration is given by the generator and the vibrations are reproduced by the dust-laden surface. The error Ay/ y is due to the accuracy of measuring the amplitude of the vibrations. In our experiments, the combined error Av/ v + Ay/y was never greater than 5%. Hence, as in the previous case, the main error in the method may be attributed to the unequal sizes of the particles. 

Direct Mass Measurement One type of densitometer measures the natural vibration frequency and relates the amplitude to changes in density. The density sensor is a U-shaped tube held stationaiy at its node points and allowed to vibrate at its natural frequency. At the curved end of the U is an electrochemical device that periodically strikes the tube. At the other end of the U, the fluid is continuously passed through the tube. Between strikes, the tube vibrates at its natural frequency. The frequency changes directly in proportion to changes in density. A pickup device at the cui ved end of the U measures the frequency and electronically determines the fluid density. This technique is usefiil because it is not affec ted by the optical properties of the fluid. However, particulate matter in the process fluid can affect the accuracy. 

For accuracy of data, a direct mechanical link between the transducer and the machine s casing or bearing cap is necessary. This makes the method used to mount the transducer cmcial to obtaining accurate data. Slight deviations in this link will induce errors in the amplitude of vibration measurement and may create false frequency components that have nothing to do with the machine. 

The observer concludes that the presence of the gw modifies the distance between free falling masses. The last thing to do in order to detect gw is thus to measure with a great accuracy the distance between two masses. But do not forget that the amplitudes of gw have been estimated in the range /i w 10... 

In order to obtain data with reduced temperature smearing, experiments were also carried out at 77 K. However, such experiments could not be carried out in. situ and the catalysts were thus exposed to air before the measurements. EXAFS data of three catalysts with Co/Mo atomic ratios of 0.0., 0.25, and 0.50 were obtained. The results show many similarities with the data recorded in situ and were fitted in a similar fashion using phase and amplitude functions of the well-crystallized model compound M0S2 recorded at 77 K. The results, which are given in Table III, show that the bond lengths for the first and second coordination shell are the same for all the catalysts and identical to the values obtained for the catalyst recorded in situ (Table II). The coordination numbers for both shells appear, however, to be somewhat smaller. Although coordination numbers determined by EXAFS cannot be expected to be determined with an accuracy better than + 20, the observed reduction... 

Prior to describing the possible applications of laser-diode fluorometry, it is important to understand the two methods now used to measure fluorescence lifetimes these being the time-domain (Tl)/4 5 24 and frequency-domain (FD) or phase-modulation methods.(25) In TD fluorometry, the sample is excited by a pulse of light followed by measurement of the time-dependent intensity. In FD fluorometry, the sample is excited with amplitude-modulated light. The lifetime can be found from the phase angle delay and demodulation of the emission relative to the modulated incident light. We do not wish to fuel the debate of TD versus FD methods, but it is clear that phase and modulation measurements can be performed with simple and low cost instrumentation, and can provide excellent accuracy with short data acquisition times. 

In practice, recombination of structure factors involves first weighting of the phases of the modified structure factors in a resolution dependent fashion, according to their estimated accuracy or probability. Every phase also has an experimental probability (determined by experimental phasing techniques and/or molecular replacement). The two distributions are combined by multiplication, and the new phase is calculated from this combined probability distribution. The measured associated structure factor amplitude is then scaled by the probability of the phase, and we have our set of recombined structure factors. 

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