Signal-to-background

Comparing the expressions for the background rate and the signal rate one sees that the background increases as the square of the source fimction while the signal rate is proportional to the source fimction. The signal-to-background rate, 3, is then... 

Figure Bl.10.9. Plot of the reduced relative uncertainty of a double coincidence experiment as a fimction of the signal-to-background ratio. Note that the relative uncertainty decreases as the signal-to-background rate decreases.

The concentration of is determined by measurement of the specific P-activity. Usually, the carbon from the sample is converted into a gas, eg, carbon dioxide, methane, or acetylene, and introduced into a gas-proportional counter. Alternatively, Hquid-scintiHation counting is used after a benzene synthesis. The limit of the technique, ca 50,000 yr, is determined largely by the signal to background ratio and counting statistics. 

ENHANCED SIGNAL-TO-BACKGROUND RATIO WITH A HIGHLY ORDERED PYROLYTIC CARBON FILM AS AN ELECTROCHEMICAL INTERFACE... 

Shipping analysis is an extremely sensitive electrochemical technique for measuring trace metals (19,20). Its remarkable sensitivity is attributed to the combination of an effective preconcentration step with advanced measurement procedures that generate an extremely favorable signal-to-background ratio. Since the metals are preconcentrated into the electrode by factors of 100 to 1000, detection limits are lowered by 2 to 3 orders of magnitude compared to solution-phase voltammetric measurements. Hence, four to six metals can be measured simultaneously in various matrices at concentration levels down to 10 10 i. utilizing relatively inexpensive... 

Improved signal-to-background characteristics can be achieved using dual-working-electrode techniques, such as ASV with collection or subtractive ASV (but at the expense of more complex instrumentation). 

Explain clearly why a carbon composite disk electrode offers improved signal-to-background characteristics compared to a carbon disk electrode of the same geometric area. 

However, a nonzero background in the experiment always produces a small contribution from the detection events that fall in the central Nq peak. For example, a signal-to-background ratio of 7 leads to an Nc/Nl ratio of about 0.2. In the present case, an Nc/Nl ratio of 0.06 was determined. Hence, the Nc/Nl value also indicates that the present nanocrystal behaves as a single-photon source. 

An interesting variant of a CEMS counter is the parallel-plate avalanche counter (PPAC) [18, 19], which carries the sample between parallel electrodes made of Perspex coated with graphite (Fig. 3.8, left). A counter gas is used to amplify the low conversion-electron current emitted by the sample, with an avalanche effect taking place between the plates. Compared with the CEMS proportional counters, PPAC gives a larger signal-to-background ratio, faster time response, simpler construction, and better performance at low temperatures. 

Assay conditions as determined by ASSAY VALIDATION are performed in the chosen PLATE FORMAT with an acceptable signal to background ratio as described by the Z factor. 

It was found that the concentration limit for the detection of Cys was 100 pM with 100 nM of the probe, where the signal to background rations reached 12 times. In addition, the probe was effectively applied to the imaging of thiol species in living human cells (HeLa cells). 

The low y-ray intensity relative to the K x-ray background therefore presents a problem of obtaining a reasonably good signal-to-background ratio. 

SBR signal-to-background ratio T2 spin-spin or transverse relaxation... 

BSA-blocked slides exhibifed reduced backgrounds over fhose blocked with succinic anhydride. However, succinic anhydride-blocked epoxy slides appeared to be less variable. Microarrays created on unblocked epoxysilane glass exhibited the greatest hybridization S B (signal to background noise) efficiency. 

Figure 3.23 Hybridization signal to background (S B) levels for cDNA vs. oligonucleotide probe. (From Taylor, S. etal.. Nucleic Acid Res., 31(16), 1-19, 2003. With permission.)...

PET offers the possibility to quantitatively measure the myocardial blood flow (MBF). MBF tracers can be divided into two groups. The first group is freely diffusible and represented by [ 0]H20. These tracers do not show any specific absorption and their distribution is completely determined by diffusion. Consequently, the measurement of the MBF is based on the first-pass extraction and clearance data. Because of the low heart-to-blood radioactivity ratio, the freely diffusible tracers provide myocardial images with low signal-to-background ratios. The second class is composed of highly extractable heart tracers. The tracer p NjNHs belongs to this family. These radiolabeled compounds are characterized by a selective extraction and retention in the myocardium. The... 

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