Probe Types

A brief description of probe types and their characteristics would be appropriate Absolute Probes... 

By variation of ceramic volume fraction and selection of the best fitting PZT material we can as well adjust the dielectric constant of the piezocomposite within a wide range. Therefore, we can choose the best piezocomposite material for each probe type to get optimum pulse form and amplitude. 

However, this probe design is dedicated to a special turbine blade type and a special inspection task on this blade. But similar probe types and probe holders can be provided also for other engine types and for other inspection tasks like wall thickness measurement and crack detection in other zones of a blade. 

A standard probe (type MWB or SWB) is fixed to the probe holder and is mechanically connected to a further piezoelectric receiver. A noise generator, which is coupled to any point of the test object, provides a low frequency noise signal which is picked up by the piezoelectric receiver. The intensity of the signal allows the evaluation of the coupling quality. 

Sampled scan data would be a benefit when it comes to certification of new inspectors or re-certification of existing staff. A large database of scans could be compiled and used randomly at test centres, which would help to avoid the samples becoming too familiar. Examinations could also be more easily tailored to the probes, types of materials and types of defects the inspector is likely to see. 

The measurement range of a thermistor is dependent on the probe type, typically -100 to +300 °C. The stability is not as good as that of metallic resistances. Thermistors are not standardized like some of the metallic probes. The thermistor has the advantage of a high change of the resistance with temperature. A very wide variety of sizes and shapes and a low price makes them attractive in relation to the metrological performance. 

SWNTs (HiPco, Carbon Nanotechnologies Incorporated) were shortened by ultrasonication with a probe-type sonicator in mixed acids (H2SO4 and HNO3) under ice-cooling. After diluting the mixture with water (MiliQ), the shortened SWNTs were purified by filtration through a PTFE membrane filter (pore size 1 pm or 0.2 pm) or by chromatography (Sepadex G-50). 

As described in Section 7.4.2, one of the challenges of online LC-NMR is the need to match the chromatographic peak to the active volume of the CapNMR flow cell. An excellent discussion of the comparison of CapLC-NMR with other NMR probe types has been provided by Lewis et al. [17] Table 7.1 shows the sensitivity comparison of the CapNMR probe with larger volume probes. It is important to note that the experimental design used by these authors adjusted the concentration of analyte such... 

The two main types of electromechanical transducers are based on either the piezoelectric or the magnetostrictive effect. The more commonly used of which are piezoelectric transducers, generally employed to power the bath and probe type sonicator systems. Although more expensive than mechanical transducers, electromechanical transducers are by far the most versatile and widely used. 

As noted above this type of mechanical transducer is predominantly used for homo-genisation/emulsification. These devices differ markedly from the more usual bath and probe types in that they derive their power from the medium (by mechanical flow across the blade) rather than by the transfer of energy from an external source to the medium. The majority of the chemical effects observed on using whistle type transducers for the sonication of homogeneous reactions can be attributed mainly to the generation of very fine emulsions rather than the ultrasonic irradiation itself. 

Solutions to the problem of the scale-up of sonochemical reactions do exist but they are not so simple as the use of bigger versions of laboratory equipment. In a production situation the volumes treated vill be very much larger than those considered in the laboratory and the type of process vill govern the choice of reactor design. It could well be that some processes would be more suited to low intensity sonication (e. g. using a bath type reactor) whereas others may need higher intensity irradiation via a probe type system). 

The double-beam phosphate-glass Nd laser apparatus used in these experiments has been described elsewhere (3,4). Experiments were of the pump-probe type done at a rate of one per minute using a 531 nm (8 ps FWHM, TEM, 1 mj ) pulse to initiate the photodissociation... 

Bio)chemical sensors can be used in both the batch and the continuous mode. While this is also true of probe-type sensors, flow-through sensors can only be used in a continuous regime coupled on-line to a continuous-flow configuration. 

Compatibility between sensors and automatic and automated analytical systems is crucial as it allows two Analytical Chemistry trends to be combined (see Fig. 1.1). Probe-type and planar sensors can be used in automated batch systems including robot stations, as well as in continuous (mixed in-line/on-line) systems. On the other hand, flow-through sensors are only compatible with continuous configurations. 

One of the most valuable assets of flow-through (bio)chemical sensors is their compatibility with unsegmented-flow configurations, which endows them with major advantages over probe-type sensors including higher flexibility and automatability in addition to wider applicability to real rather than academic problems — the former are rarely addressed by using sensors. 

Table 4.1. Comparison of the performance of a probe-type and a flow-cell type sensor for fluoride...

Parameter Probe-type sensor Flow-cell type sensor... 

The flow injection manifold shown in Fig. 5.5.A, which includes a probe-type fluorimetric biosensor accommodated in a thermostated flow-cell at 35°C, was used for the determination of L-glutamate in foods and... 

Figure 5.8 — Probe-type sensor based on continuous circulation of a stream containing an acid-base indicator for the batch determination of COj in sea water, (a) Reagent delivery capillary, (d) Reagent exit capillary, (c) Optical fibre from source, (d) Optical fibre to detector, (e) White silicone rubber membrane. (/) White silicone sealant, (g) Epoxy resin, (/i) 0-ring. (/) Sensor housing. (/) Optical cable. (Reproduced from [12] with permission of the American Chemical Society).

Recently, DeGrandpre [12] developed a probe-type sensor for the determination of PCO2 in sea water by direct immersion of the probe, which, however, has some connotations of flow-through sensor even though a pH indicator such as Phenol Red (piTj = 7.5) or Bromothymol Blue (pAn = 6.8) rather than the sample is circulated over the sensing microzone —the basic forms of these indicators have a high molar extinction coefficient at 560 and... 

Suzuki et al. [90] developed a diffuse refleetanee flow-through sensor for improving selectivity in the determination of lithium in human fluids, where sodium can occur at concentrations up to 10 000 times higher than that of the analyte. The mechanism on which the sensor action relies (Fig. 5.21.2) was previously exploited by the authors to develop a probe-type sensor for potassium [91]. The sensor response is based on an A -H exchange according to... 

Fluorimetric (the others are photometric) Probe-type ISPD (ion-selective photodiode)... 

Many methods of investigation of protein-ligand binding kinetics that are based on linear processes are of a pump-probe type. In this approach an optical pulse, called a pump, starts a photoreaction (such as dissociation of MbCO into Mb and CO), and its progress is probed a time At later. The probe could be, for example, a weak laser pulse, which detects the spectral changes in the heme during the protein-ligand recombination, or an x-ray pulse, which allows determination of the protein structure at a particular instant in time. 

Using time-resolved crystallographic experiments, molecular structure is eventually linked to kinetics in an elegant fashion. The experiments are of the pump-probe type. Preferentially, the reaction is initiated by an intense laser flash impinging on the crystal and the structure is probed a time delay. At, later by the x-ray pulse. Time-dependent data sets need to be measured at increasing time delays to probe the entire reaction. A time series of structure factor amplitudes, IF, , is obtained, where the measured amplitudes correspond to a vectorial sum of structure factors of all intermediate states, with time-dependent fractional occupancies of these states as coefficients in the summation. Difference electron densities are typically obtained from the time series of structure factor amplitudes using the difference Fourier approximation (Henderson and Moffatt 1971). Difference maps are correct representations of the electron density distribution. The linear relation to concentration of states is restored in these maps. To calculate difference maps, a data set is also collected in the dark as a reference. Structure factor amplitudes from the dark data set, IFqI, are subtracted from those of the time-dependent data sets, IF,I, to get difference structure factor amplitudes, AF,. Using phases from the known, precise reference model (i.e., the structure in the absence of the photoreaction, which may be determined from... 

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