Multichannel Systems

Increased throughput can be obtained by using multichannel geometries, but the droplet size distribution may become broader. Various planar and three-dimensional interdigital mixers, with or without focusing, were investigated for water-oil and 

A few devices have been proposed that resemble cross-flow membrane emulsification, where a phase is induced to disperse through the small openings of a membrane in a flow of continuous phase [3]. Such processes are more energy efficient than conventional approaches such as colloid mills and homogenizers [142]. A microstructured analogue of membrane emulsification was presented by de 

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Coupling channels. In multichannel systems, a coupling channel is used as the equivalent to an n-channel intensity stereo system. This system is also known under the names dynamic crosstalk or generalized intensity coding. Instead of n different channels, for part of the spectrum only one channel with added intensity information is transmitted. Coupling channels are used in AC-3 ([Fielder et al., 1996]) and MPEG-2 AAC ([Johnston et ah, 1996]). 

For either multiplex (e.g., FT-Raman) or multichannel (e.g., CCD) spectrometers, tM is the appropriate time to insert in Eq. (3.6) or (3.7). Second, a multichannel system can obtain a complete spectrum 1/Nr times faster than a single-channel system, while maintaining the same measurement time and signal strength per resolution element. Of course, both of these statements assume that other variables are equal for both spectrometer types. In Chapter 4, we will see that Im strongly affects SNR, but that the effects are fundamentally different for multichannel as opposed to multiplex spectrometers. 

Figure 4.8. Spectra of glassy carbon (a hard form of sp carbon) with single-channel and multichannel spectrometers. The multichannel system (Nr = 512) achieved higher SNR with shorter measurement time and lower laser power.

So Esnr is decreased for the single-channel instrument when compared to a multichannel system with Nr resolution elements. 

After consideration of the properties of dispersive/CCD Raman spectroscopy and FT-Raman, questions about alternative approaches to conventional FT-Raman often arise. First, can fluorescence be further reduced by using still longer laser wavelengths Second, wouldn t the best solution be a shot-noise-limited multichannel system operating above 1000 nm Both of these questions have been addressed experimentally, but given current technology the associated hardware developments are not yet ready for widespread use. 

Although AAS, FES, or spectrophotometric methods may be used for Na and K" analysis, most laboratories now use ISE methods. Of approxhnately 5400 laboratories reporting College of American Pathologists (CAP) proficiency data for Na and K , >99% were using ISE methods in 2003. The principles of each of these approaches (which are discussed in detail in Chapters 3 and 4) are the same whether the instrumentation is dedicated or integrated into a multichannel system. 

The spectrophotometer shown in Figure 25-21 can be controlled by most personal computers. The instrument (without the computer) can be purchased for about 10,000. Several instrument companies are combining aixay detector systems with fiber-optic probes that transport the light to and from the sample. These instruments allow measurements in convenient locations that are remote to the spectrometer. We are beginning to see more CCD and CID detectors used in multichannel systems, particularly when advantage can be taken of the two-dimensional nature of these detectors for imaging purposes (see color plate 14). 

Actions by plant operating personnel, if required, to compensate for the deviation and to maintain the plant within the limits and conditions for normal operation. For multichannel systems, this may involve placing the failed component or channel in a fail-safe state until repairs and testing have been completed. Notification of management at the appropriate level of the operating organization. 

Multichannel systems were produced for clinical analysis. Before microprocessors were available for calculating results, these systems used a combination of hydraulic phasing and mechanical timers to switch the steady-state part of each peak sequentially for each channel onto calibrated chart paper. 

A simultaneous WDXRF system, also called a multichannel system, uses multiple channels, optimized for a specific element or background measurement. Each individual channel consists of a crystal, detector, and electronics module and is dedicated to a specific wavelength. Instruments with as many as 38 fixed crystal/detector channels or as few as two are available. These systems are designed for specific applications, such as the analysis of steel in a production facility where hundreds of samples must be analyzed very quickly (e.g., in less than 60 s) for the same suite of elements every day. 

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