Drift time, average

The Average Drift Time or the time it takes the monitor to respond to changes in concentration can be calculated from Equation 2 ... 

For a path length of. 65 cm and diffusion rate of 0.12, the response time (Average Drift Time) is less than two seconds. In other works, the monitor responds to changes in concentration of most organics in the atmosphere it is sensing, within two seconds. 

Provided that real polycrystalline samples are subject of a spatially non-homogeneous distribution of traps near the sample surface and within intergrain boundaries, the pretransit time averaged carrier flux is composed of two comparable parts one due to usual carrier drift in the external field and the second due to carrier diffusion [see Eq. (198) and Sec. 4.4] ... 

Attention should be drawn to the fact that there has been a degree of inconsistency in the treatments of ionic clouds (Chapter 3) and the elementary theory of ionic drift (Section 4.4.2). When the ion atmosphere was described, the central ion was considered—from a time-averaged point of view—at rest. To the extent that one seeks to interpret the equilibrium properties of electrolytic solutions, this picture of a static central ion is quite reasonable. This is because in the absence of a spatially directed field acting on the ions, the only ionic motion to be considered is random walk, the characteristic of which is that the mean distance traveled by an ion (not the mean square distance see Section 4.2.5) is zero. The central ion can therefore be considered to remain where it is, i.e., to be at rest. 

The second case shows very different behavior The relative concentrations of the degenerate master sequences are subject to random drift, and the dominant eigenvector of W represents at best a time average of the mutant distribution. Then the dynamics can be modelled only by a stochastic process requiring careful choice of the appropriate mathematical technique and approximations in a hierarchy of equations (see refs. 48 and 51 and Section V.2). One difficulty here is that even very distant mutants contribute if sufficiently neutral. The results of Section III.2 indicate that there is (almost... 

Here A and B are instrumental constants, m and q are the mass and charge of the ion and Vg is the velocity component along the drift tube axis. Thermal ions arrive at the detector in a time given by the first term, forward ions (labelled Nf ) with momentum mv, < 0 (i.e. ejected initially towards the detector) arrive at an earlier time and backward ions (labelled Nb ) with mv, > 0 arrive at a later time. A typical low-resolution, time-averaged TOF spectrum of N2 at the bottom of Fig. 4 shows the double-peaking that results. 

In this section we derive the drift-flux mixture model starting out from the time averaged multi-fluid model expressed in terms of phase- and mass weighted variables [112]. The relative moment of the phases is given in terms of drift velocities. This approach can be applied for systems where the phase densities are constants and the interface mass transfer can be neglected. 

At equilibrium, the arrival or drift time of the single peak is the number-weighted average of the drift times of the two constituent ions as described by Equation 13.6. When the times spent as the individual ions are mzh+> respectively, it fol-... 

NO + impurity + CH3I (Reprinted with permission from [8]. Photoionization method was used to form the free electrons, and the drift gas was maintained at atmospheric temperature. These spectra were averaged ovct 20 scans, and the drift times were adjusted for a uniform drift potential of —500 V)... 

For a drift tube of length L= 10 cm, the average drift time can be estimated as... 

One source of such constraints could be the orientationally averaged cross section obtained from imi mobility. At the end of Sect. 3.2.2 we discussed the use of drift tube ion mobdity as a conformational filter for cryogenic ion spectroscopy but didn t mention the information content obtained from IMS. The cross section determined from the drift time in such an experiment could, in principle, be used as a filter in the conformatimial search procedure by comparing the cross sections of candidate structures to the measured value. While this would require a fast calculation of the cross section, for use as a conformational filter this could be done with reduced accuracy. 

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