Low-intensity background

The spin-echo successfully imaged water held in the cracks of cement paste. This technique can be used to resolve cracks much smaller than the nominal resolution by relying on water saturation of the crack, the connectivity of the crack structure and the fact that it is relatively easy to detect a high intensity structure on a low intensity background. 

Below, we illustrate how such multiple filaments are concurrently created at different transverse and longitudinal locations, and how they interact with the low-intensity background. It was first proposed in [15] that such an interaction is crucial for long distance propagation of high-power femtosecond pulses in air. The basic idea is that of dynamic exchange of energy between multiple, essentially unsynchronized and spatially sharply localized filament cores and the low-intensity, spatially wide pedestal of the beam. 

Fig. 13.3. Transverse profile of the fluence (time-integrated intensity) measured at several propagation distances. The color scheme was chosen such that one can see the structure of the low-intensity background. On the other hand, it makes it difficult to compare filament intensities. The size of the depicted domain in all panels is 1 cm X 1 cm...

Both APCI and ESI produce low intensity background signals of the peak-at-every-mass type (Guo 2006) that can Unlit the S/B value and thus ultimately limits of detection and quantitation when MS monitoring is used (fuU scan or selected ion recording, SIR). One way to improve this situation is to use MS monitoring (MRM, Section 6.2.2), since it is unlikely that the background... 

Figure 17.9 (A) Photoluminescence intensity traject07 (gray) of a CdSe-ZnS quantum dot. The high intensity level is the on state and the low intensity level is the off state. The trace in black is the background intensity. Reprinted with permission from reference [14] copyright [2005], American Chemical Society. (B) Schematic...

In the absence of analyte, many CL systems show a low emission background level. Hence, in flow systems, as the CL intensity is proportional to the analyte concentration, the emission appears as a sharp peak superimposed on a low constant blank signal, which is measured when the mixture of analyte and CL reagents passes through the detector cell. Because only a small portion of CL emission is measured from this time profile, nonlinear calibration curves may be obtained for reactions with complex kinetics [1],... 

ORC) pretreatment were digitally subtracted from the spectra acquired after the ORC. The resulting spectra in this frequency region demonstrate a smaller influence from the background and allow accurate quantitation of peak areas even at low intensity. 

Example The significant increase in sensitivity and the improvements of sig-nal-to-background ratio (Chap. 5.2.4) in CF-FAB spectra are demonstrated by comparison of the standard FAB and CF-FAB mass spectra of peptides. [108,116] In case of 10 pmol of the peptide des(gln)-substance P (Fig. 9.16) solely CF-FAB reveals the low-intensity signals due to some loss of side chain groups and several a-type fragments. 

In addition, color film has an inherent artifact in areas of overexposure, in which the color of the film becomes yellow, no matter what the color of the exposing light. This produces apparent areas of enhanced concentration, which may or may not reflect the true intensity of label, especially in areas in which a low-level background image is added to the specific signal. This can lead to misinterpretations about selective areas of concentration of label. 

One of the limitations associated with the use of fluorogenic dyes as labels for nucleic acids is the relatively high background fluorescence intensity in solution. This problem can be ameliorated by the use of asymmetric cyanine dyes. Another approach that can achieve low fluorescence background is based on the use of FRET pairs. If the acceptor and donor are in close proximity to... 

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