Duration of the pulse

Block 4 a high-voltage generator of the probe pulse, the output value of the amplitude is from 100 to 400V, the duration of the pulse is from 15 to 300 ns. 

When a pulsed laser is used, ions are only produced for the duration of the pulse, i.e. they are not produced continuously and the mass spectrometer used must be capable of producing a mass spectrum from these pulses of ions. As discussed below in Section 3.3.4, the time-of-flight (ToF) mass analyser is the most appropriate for this purpose and has the added advantage of being able to measure very high m/z ratios. Indeed, the recent dramatic developments in the performance of the ToF mass analyser have largely been occasioned by the requirement to produce useful spectra from MALDI. 

Flash photolysis of benzoyl and naphthoyl diazomethane, which should exist in the s-cis conformation, led to ketene intermediates within the duration of the pulse ( 20 ns).241... 

The energy imparted to the ions depends on the energy of the rf pulse and the duration of the pulse. The energy does not have to be raised in one event but may be absorbed by the ion in small portions. A technique called sustained off-resonance excitation (SORT) (82) uses a low-amplitude rf pulse that is off-resonance to the ion cyclotron frequency. The difference of the cyclotron frequency and the excitation frequency (-500 Hz) causes the ion to experience in- and out-of-phase excitation that has the effect of a repeated expansion and shrinkage of the cyclotron orbit. In this process, the ion undergoes a large number of low-energy collisions and the Ecom slowly increases until the ion dissociates. 

Pulse fluorometry The sample is excited by a short pulse of light and the fluorescence response is recorded as a function of time. If the duration of the pulse is long... 

Deposition can be carried out potentiostatically, with a copper cycle deposition potential of 0.17 V versus SCE and a nickel depKJsition cycle of 1.19 V versus SCE. The durations of the pulses can be set to give the desired thicknesses, and for each experiment the number of coulombs passed in the copper and the nickel deposition time segments can be controlled. Deposition of samples can typically be made onto commercial poly crystalline copper sheet supplied by, say, Ventron (Alpha Products), and this copper substrate can be dissolved subsequently by immersion in an NH4OH/H2O2 solution. 

Comparison of the results of the one-dimensional gradient supported 31P/15N 1H -se-HSQC experiment with phase-cycled HSQC and HMQC experiments gave relative S/N-ratios of 0.75 0.92 1 which was, under consideration of the suppression of one of the two possible coherence transfer pathways by the field gradients and the longer duration of the pulse sequence, interpreted in terms of a very good performance.25 The main benefits of the PFG-es-HSQC sequence were seen, however, in the excellent level of artefact suppression which allowed one to observe correlations via very small couplings even in cases where the active isotopomer is present in low natural abundance and its lines are normally obscured by residual parent signals (Fig. 3). 

The use of strong fields to drive the dynamics leads to somehow similar effects than those of ultrafast pulses. If the Rabi frequency or energy of the interaction is much larger than the energy spacing between adjacent vibrational states, a wave packet is formed during the laser action. The same laser can prepare and control the dynamics of the wave packet [2]. Both short time widths and large amplitudes can concur in the experiment. However, the precise manipulation of dynamic observables usually becomes more difficult as the duration of the pulses decreases. 

The mathematics outlined in this section are fairly well applicable to a technique named differential pulse polarography [21, 48, 50]. The potential is programmed as a sequence of normal potential steps each with a small amplitude potential pulse superimposed [see Fig. 14(a)]. The problem of separating the small amplitude current is met by sampling the current at two different moments in one period (i) just before the application of the small amplitude pulse, i.e. at t t0 and (ii) at a moment tm — t0 + tp within the duration of the pulse. The difference of the two samples is recorded as a function of E. It is not difficult to... 

The finite duration of the pulse in a way causes the same kind of problems,... 

Fig. 9.2. Saturation effect of the modified DANTE sequence on a signal off-resonance with respect to the carrier frequency. The trajectory of the in-plane component of the magnetization is shown. The z magnetization is tilted by the first small angle pulse toward the x axis, and starts precessing toward the y axis. The duration of the pulse corresponds to the duration of a 90s precession, so that at the end of the first pulse the projection lies on the y axis. The phase of the following pulses is rotated in phase with the precession of the signal, in such a way as to follow the spin magnetization in its spiral movement toward the xy plane.

In a record obtained by the patch clamp technique, the channel is closed for much of the time (i.e. no current flows across the patch of membrane that contains it), but at irregular intervals the channel opens for a short time, producing a pulse of current. Successive current pulses are always of much the same size in any one experiment, suggesting that the channel is either open or closed, and not half open (there are exceptions to this rule). The durations of the pulses, however, and the intervals between them, vary in an apparently random fashion from one pulse to the next. Hence the openings and closings of channels are stochastic events. This means that, as with many other molecular processes, we can predict when they will occur only in terms of statistical probabilities. But one of the most useful features of the patch clamp method is that it allows observation of these stochastic changes in single ion channels as they actually happen individual protein molecules can be observed in action. 

In square-wave voltammetry74 82, a symmetrical square-wave pulse (Fig. 2.14a) is superponated to a staircase wave (Fig. 2.14b) resulting in the square wave (Fig.2.14c). The duration of the pulse, t, is equal to the length of the staircase, and the superponation is obtained in such a way that the forwards pulse of the square wave coincides with the first half of that staircase. Two other important parameters are ESVI, the pulse height of the square wave, and Esc, the increase of the staircase for each step. 

The DNMPV is the multipulse variant of the DMPV technique such that the duration of the period between pulses and the duration of the pulses are similar ... 

Since in this technique the duration of the pulse (tp) is much shorter than the period between pulses (t1 see Scheme 7.2), the response of reversible processes in DMPV is totally coincident with that obtained in the double pulse technique DDPV [9],... 

M 4] [P 3] Temperature differences of 5-10 °C result by the action of the AC field owing to Joule heating for the 3 s duration of the pulse [25], The data were gathered from both thermocouple measurements and capacitance-based heat transfer analysis. 

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