Rectangular pulse technique

The BET surface area was measured by N2 adsorption at 77K with a flow type apparatus. The OH density of the support was measured by TG (Rigaku, TG 8120) and by the reaction with CH3MgI [12]. The amount of deposited V2O5 was analyzed by ICP (Jarrel-Ash MODEL 975). The XRD pattern was measured with CuKa radiation (Rigaku RINT-1200). The density of surface V=0 species was measured by NO-NH3 rectangular pulse technique... 

This observation led Murakami and coworkers to develop a new method to measure the concentration of V=0 species on oxidized vanadium oxide-based catalysts [10,11]. The method known as rectangular pulse technique involves the reaction of NO and NH3 with surface V=0 species to produce molecular nitrogen according to the following stoichiometric reaction ... 

Figure 5-28 (a) The result of Fourier transformation of a low-power rectangular pulse, (b) The result for a shaped Gaussian pulse. (Reproduced from T. D. W. Claridge, High-Resolution NMR Techniques in Organic Chemistry, Pergamon Press, Amsterdam, 1999, p. 349.)... 

In recent years the flyer plate technique of determining shock sensitivity has become very popular (eg, Refs 11,30,37, 51,55, 59, 60, 61, 64,65 Sc 66. It has the distinct advantage of delivering a plane-wave rectangular pulse of known duration to the test expl. Also the amplitude and duration of these shocks can be varied over a wide range... 

In the switched-mode technique, the mains power signal is rectified and smoothed it is then switched as rectangular pulses at a frequency of 25 kHz into a ferrite transformer to obtain the desired voltage finally, it is rectified and smoothed to provide the required power to the instrument. The combination of modem transistor switching circuits with... 

The experimental performance is depicted in Fig. 2.18. The modulation frequency = 2nf is tripled by forming rectangular pulses, where the third harmonic is filtered and fed into the reference input of a lock-in amplifier that is tuned to 3f2. Figure 2.19 illustrates this technique by the third-derivative spectrum of the same hfs components of I2 as obtained with the intermodulated fluorescence technique in Fig. 2.13. 

The third block in Fig. 2.1 shows the various possible sensing modes. The basic operation mode of a micromachined metal-oxide sensor is the measurement of the resistance or impedance [69] of the sensitive layer at constant temperature. A well-known problem of metal-oxide-based sensors is their lack of selectivity. Additional information on the interaction of analyte and sensitive layer may lead to better gas discrimination. Micromachined sensors exhibit a low thermal time constant, which can be used to advantage by applying temperature-modulation techniques. The gas/oxide interaction characteristics and dynamics are observable in the measured sensor resistance. Various temperature modulation methods have been explored. The first method relies on a train of rectangular temperature pulses at variable temperature step heights [70-72]. This method was further developed to find optimized modulation curves [73]. Sinusoidal temperature modulation also has been applied, and the data were evaluated by Fourier transformation [75]. Another idea included the simultaneous measurement of the resistive and calorimetric microhotplate response by additionally monitoring the change in the heater resistance upon gas exposure [74-76]. 

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