Ratio detection

Two main difficulties stand in the way of mass spectrometric determinations of 02(1A9) or 02(1Sp+) concentrations in reaction systems. In the first place, the ratio [02 ]/[02] must be relatively high for the detection of 02, and this probably limits observations to the state, and even then to discharge systems. Robertson has shown37 that for a thermal electron beam of temperature 7 the minimum detectable ratio of [02 ]/[02] is given by the relation... 

Normal conditions. The maximum and minimum values of each area pulse was computed and then subtracted from each other to obtain the pulse amplitude at all values of cuff pressure. The amplitude curve is then normalized by the maximum overall amplitude. This analysis yields the oscillation amplitude curve shown in Figure 12.3. The amplitudes of the oscillations may be further analyzed to determine the arterial blood pressure provided the systolic and diastolic detection ratios are known. Hence, the oscillation amplitude curve is all that is required to determine blood pressure by means of oscillometry. If the oscillation amplitude curve is altered by any parameter, it will result in blood pressure determination error. 

Drzewieckl G., Hood R., Apple H. Theory of the oscillometric maximum and the systolic and diastolic detection ratios. Ann. Biomed. Eng. 22(l) 88-96,1994. 

Ogasawara, Y., Mukai, Y., Togawa, T., et al., 2007. Determination of plasma thiol bound to albumin using affinity chromatography and high-performance liquid chromatography with fluorescence detection ratio of cysteinyl albumin as a possible biomarker of oxidative stress. J. Chromatogr. B Analyt. Technol. 

In a mass spectrometer, the molecules, in the gaseous state, are ionized and fragmented. The fragments are detected as a function of their mass-to-charge ratio, m/e. The graphical representation of the ion intensity as a function of m/e makes up the mass spectrogram as illustrated In Figure 3.1. 

The detectability of critical defects with CT depends on the final image quality and the skill of the operator, see figure 2. The basic concepts of image quality are resolution, contrast, and noise. Image quality are generally described by the signal-to-noise ratio SNR), the modulation transfer function (MTF) and the noise power spectrum (NFS). SNR is the quotient of a signal and its variance, MTF describes the contrast as a function of spatial frequency and NFS in turn describes the noise power at various spatial frequencies [1, 3]. 

Sandborg, M. and G. Alm-Carlsson, Influence of x-ray energy spectrum, contrasting detail and detector on the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) in projection radiography. Phys. Med. Biol., 1992. 37(6) p. 1245-1263. 

In fig. 2 an ideal profile across a pipe is simulated. The unsharpness of the exposure rounds the edges. To detect these edges normally a differentiation is used. Edges are extrema in the second derivative. But a twofold numerical differentiation reduces the signal to noise ratio (SNR) of experimental data considerably. To avoid this a special filter procedure is used as known from Computerised Tomography (CT) /4/. This filter based on Fast Fourier transforms (1 dimensional FFT s) calculates a function like a second derivative based on the first derivative of the profile P (r) ... 

A corresponding composite probe with the same frequency and crystal size, however, detects the test flaw much better the echo has a 12 dB higher amplitude (see Fig. 4) and in addition, the noise level is much lower, resulting in an improved signal to noise ratio. This effect is especially observed at high sound attenuation. However, in materials with low attenuation or in case of shorter sound paths the standard probe yields a comparable good signal to noise ratio. 

Based upon a piezoelectric 1-3-composite material, air-bome ultrasonic probes for frequencies up to 2 MHz were developped. These probes are characterized by a bandwidth larger than 50 % as well as a signal-to-noise ratio higher than 100 dB. Applications are the thickness measurement of thin powder layers, the inspection of sandwich structures, the detection of surface near cracks in metals or ceramics by generation/reception of Rayleigh waves and the inspection of plates by Lamb waves. 

A measurement procedure has been developed that allows to determine the mass of the inclusions as well as their locations with respect to radius, angle, and depth (2). For the depth determination use is made of the approximate 1/R dependence of the magnetic field strength from the distance R to the inclusion When in a first measurement at a small lift off an inclusion is detected, the measurement is repeated at an increased lift off From the signal ratio the depth can be calculated or seen from a diagram like fig. 5a which was generated experimentally. After that, from calibration curves like fig. 5b the absolute value of the signal leads to the mass of the inclusion. 

A connnon teclmique used to enliance the signal-to-noise ratio for weak modes is to inject a local oscillator field polarized parallel to the RIKE field at the detector. This local oscillator field is derived from the probe laser and will add coherently to the RIKE field [96]. The relative phase of the local oscillator and the RIKE field is an important parameter in describing the optical heterodyne detected (OHD)-RIKES spectrum. If the local oscillator at the detector is in phase with the probe wave, the heterodyne mtensity is proportional to... 

Figure Bl.7.18. (a) Schematic diagram of the trapping cell in an ion cyclotron resonance mass spectrometer excitation plates (E) detector plates (D) trapping plates (T). (b) The magnetron motion due to tire crossing of the magnetic and electric trapping fields is superimposed on the circular cyclotron motion aj taken up by the ions in the magnetic field. Excitation of the cyclotron frequency results in an image current being detected by the detector electrodes which can be Fourier transfonned into a secular frequency related to the m/z ratio of the trapped ion(s).

In the other types of mass spectrometer discussed in this chapter, ions are detected by having them hit a detector such as an electron multiplier. In early ICR instruments, the same approach was taken, but FT-ICR uses a very different teclmique. If an RF potential is applied to the excitation plates of the trapping cell (figure B 1.7.18(b)) equal to the cyclotron frequency of a particular ion m/z ratio, resonant excitation of the ion trajectories takes place (without changing the cyclotron frequency). The result is ion trajectories of higher... 

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