Time-of-flight profile

In an early study, Greenleaf et al. [4] reported reconstructions of ultrasonic velocity from time-of-flight profiles. Since then there has been periodic activity in using ultrasound to determine the transmission properties attenuation or refractive index. 

Greenleaf, J.F. Johnson S.A. Samayoa, W.F. and Duck, F.A. (1975). Algebraic reconstruction of spatial distributions of acoustic velocities in tissue from their time-of-flight profiles. In Acoustical Holography, Vol. 6, Ed. N. Booth, Plenum Press, 71-90. 

Figure 10. The N ion time-of-flight profile following Rydbeig state excitation around n = 150 (N = 2) in the presence of a 0.3-V/cm retarding field. The dotted line shows the one-color direct ionization signal, which is subtracted from the total signal in the analysis of the results.

As an example. Figure 10 shows the time-of-flight profiles for the impact-induced fragmenution profiles of naphthalene, CioHi, ... 

FIGURE 15.2 Time of flight profiles of ground-state YbF recorded by two laser-induced fluorescence detectors, situated 340 and 1300 mm from the source. The hues are Gaussian fits to the two datasets. 

One of the key advantages to time-of-flight reflectometers comes in the measurement of fluid surfaces. Simply delivering the neutrons onto the fluid surface at a fixed angle (without moving the specimen) and detecting the reflected neutrons yields the reflectivity profile. 

In principle GD-MS is very well suited for analysis of layers, also, and all concepts developed for SNMS (Sect. 3.3) can be used to calculate the concentration-depth profile from the measured intensity-time profile by use of relative or absolute sensitivity factors [3.199]. So far, however, acceptance of this technique is hesitant compared with GD-OES. The main factors limiting wider acceptance are the greater cost of the instrument and the fact that no commercial ion source has yet been optimized for this purpose. The literature therefore contains only preliminary results from analysis of layers obtained with either modified sources of the commercial instrument [3.200, 3.201] or with homebuilt sources coupled to quadrupole [3.199], sector field [3.202], or time-of-flight instruments [3.203]. To summarize, the future success of GD-MS in this field of application strongly depends on the availability of commercial sources with adequate depth resolution comparable with that of GD-OES. 

There are two main methods to measure velocity fields and profiles using NMRI time-of-flight velocimetry (TOF) and phase encoding velocimetry. In this section these methods are briefly described with a discussion of how they were used to perform accurate velocity measurements in oil-in-water emulsions. These methods... 

Cain,T. Lubman, D. Weber, W. J. Differentiation of bacteria using protein profiles from matrix assisted laser desorption/ionization time of flight mass spectrometry. Rapid Comm. Mass Spectrom. 1994,8,1026-1030. 

Chong BE, Lubman DM, Miller FR, et al. Rapid screening of protein profiles of human breast cancer cell lines using non-porous reversed-phase high performance liquid chromatography separation with matrix-assisted laser desorption/ionization time-of-flight mass spectral analysis. Rapid Commun. Mass Spectrom. 1999 13 1808-1812. 

Proteomics has the potential to revolutionize diagnosis and disease management. Profiling serum protein patterns by means of surface-enhanced laser desorption/ion-isation time of flight (SELDI-TOFF) mass spectrometry is a novel approach to... 

M. Vazquez Pelaez, J. M. Costa-Fernandez, R. Pereiro, N. Bordel and A. Sanz-Medel, Quantitative depth profile analysis by direct current glow discharge time of flight mass spectrometry, J. Anal. At. Spectrom., 18,2003, 864-871. 

Superior sensitivity, efficiency, and specificity have made high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS), the predominant analytical technique for characterization and quantitative analysis of metabolites (Kostiainen et al., 2003 Ma et al., 2006 Prakash et al., 2007). Ion trap, triple-quadrupole, and quadmpole time-of-flight (Q-TOF) mass spectrometers are routinely used to profile and characterize metabolites in plasma and excreta (Ma et al., 2006). The combination of scan types and features available on mass spectrometers of different design (product ion, MS", neutral loss, precursor ion scans, accurate mass measurements) allows identification and characterization of putative and unexpected metabolites with or without little prior knowledge of biotransformation pathways of a given dmg molecule. 

The ESI-LC/MS-based approaches that feature ion trap (Gatlin et al, 1998 Washburn et ah, 2001) and quadrupole time-of-flight (QTOF) (Blackburn and Moseley, 1999) mass spectrometers are routinely used for the identification and characterization of proteins. Nanoelectrospray LC/MS formats (Figure 6.3) are used to provide lower limits of detection and fully automated sample preconcentration and desalting. On-line LC/MS approaches for protein expression profiling are also used with ESI-TOF (Banks and Gulcicek, 1997 Chong et al., 2001) and ESI-Fourier transform (FT) (Kelleher... 

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