Frequency Modulation composite

The composite frequencies have been preserved in modulation experiments with two unharmonic frequencies (Fig. 10.18 Kikas et al., 2001). The coherence spectra are relatively immune to the presence of white noise, as is shown by the red spectrum in Fig. 10.18. No effect on information content was observed with flow rate or dilution up to seven times. 

Bondarev and Mardaeva were the first to observe that the Raman linewidth in mixtures could have an extra broadening, which reaches a maximum at intermediate concentrations (86). This broadening was attributed to fluctuations in the local concentration around the vibrator. This idea was elaborated theoretically by Knapp and Fisher (87). In a binary mixture of solvents, the first solvation shell of a vibration will have substantial fluctuations in composition. If the vibrational frequency is sensitive to the local composition, dephasing will result. Because it takes on the order of 10 ps for molecules to diffuse in and out of the first solvation shell, the frequency perturbations will last much longer than collisonal perturbations, and the resulting dephasing will be either in the slow modulation limit or in the intermediate range. 

When excitation of higher-order coherences are sought, P (t) blocks may be added right after a 3Q excitation Ph pulse and optimized in the same manner as above with the sole difference that blocks are inserted in increasing order of their modulation frequencies. Here, we should point out the it may be beneficial to insert FAM-II blocks rather than FAM-I blocks to provide better transfer of 3Q MQ. Sometimes, the composite pulse applied cannot be really classified as FAM-I or FAM-II and a good example is the single x — x scheme used in Refs. 78 and 97. 

A steady concentration of the reactant is not observed when the confluent reagent stream is not properly added. Pronounced differences in matrix composition (e.g., colour and suspended matter), flow rates and viscosity of the carrier and confluent streams may result in a pulsed addition of the confluent stream. The effect is random, but if the fluid-propelling device is a peristaltic pump, it is characterised by a typical frequency, dictated by the rotation speed of the peristaltic pump. A pulsating flow is then established, leading to undulations in the recorded peak. The effect is reduced if the involved streams converge with similar mean linear velocities. As the effect is characterised by a constant frequency, the modulated signal (ripple) is easily filtered out. 

For natural gas vehicles mn under closed loop control near the stoichiometric point, the composition of the controlled exhaust will modulate around the set point. The effect of the amplitude and frequency of these modulations on methane oxidation was explored. Increasing the frequency or decreasing the amplitude of exhaust modulations results in improved methane conversions, especially near the maximum methane conversion point. 

Most of the studies of methane oxidation in the literature utilize simplified feedstreams and fresh catalyst samples, generally in the form of powders or pellets. A recent paper [22] used a laboratory simulated NG vehicle exhaust to study the removal of methane, NO and CO using a Pd-only monolith catalyst. They found that optimum conversion of all three constituents occurred slightly rich of stoichiometry. These results appear to have been obtained over fresh catalyst samples. The present work utilizes monolith catalysts and laboratory simulated NG vehicle exhaust to study the effect of catalyst loading and space velocity, Ce02 addition and variations in hydrocarbon composition. The effect of modulation amplitude and frequency aroxmd the stoichiometric point was also... 

During stoichiometric testing, modulations in the exhaust gas composition, due to closed loop control on a vehicle, were simulated by pulsing additional O2 to simulate lean and CO to simulate rich perturbations into the reactor. For most tests the amplitude of these modulations was +/- 0.5 air/fuel ratio units and the frequency was 0.5 Hz. Space velocity was 46000h- ... 

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