Background rate

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.

For any region of the horizontal plane with dimensions Ar 2 unifomi background rate is... 

FIGURE 8.10 H2S consumption in rat aorta smooth muscle cells (RASMCs). Accumulated data from several experiments showing RASMC H2S consumption rates (filled circles and squares) as a function of H2S concentration, compared to H2S oxidation rates in solution without cells (open circles and squares). Heat-inactivated RASMC H2S consumption rates (open plus symbols) were equivalent to background rates without cells. Inset Representative PHSS traces showing stepwise additions of Na2S stock, at arrows, in the presence (thin line) and absence (thick line) of RASMCs (after [41]). 

Electronic noise, identified via rise-time characteristics, shown rising to 30 times background rate for 15-mL gas proportional counter. A tiny fraction of such noise, not identified by means such as pulse shape analysis, could invalidate results which presume that the background is stable to < 10%. 

Enhancement ratio, ER Quantified as k Jk Dcat, is used to express the catalytic power of a biocatalyst. It is a comparison between the catalysed reaction occurring at its optimal rate and the background rate. 

Figure 2. NO inhibits iron-induced lipid peroxidation. The rate of Oj consumption of HL-60 cells (5 X 10 /ml) was detennined using a YSI O2 monitor. Fe (20 pM) was added at the first arrow and subsequently NO (0.45 pM) was added (other arrows). When NO was added, the O2 consumption was inhibited for a period of a few min, then it resumed at near its initial rate until the reintroduction of additional NO. Also shown (lower dashed line) is a control of HL-60 cells subjected to Fe -induced oxidative stress in the absence of NO addition. The background rate of O2 uptake of the HL-60 cell suspension before the addition of Fe was 10 nM/sec. Upon the addition of 20 pM Fe, this rate increased to 220 nM/sec. The addition of NO resulted in a decrease in O2 consumption to <10 nM/sec. (From Kelley, E.E., Wagner, B.A., Buettner, G.R., and Bums, C.P., 1999, Arch. Biochem. Biophys. 370 97-104).

Some scholars use the term "background rate" to refer to the total percentage of deaths in the United States attributable to cancer—about 20 percent. See Cross, Byrd, and Lave (1991, 83). 

Scaler count rates with 6.A MeV threshold as a function of time. Hatched region is the count rate expected from the Mont Blanc burst (5 5 /2 events> burst period = 10 sec). Our data are well below the burst rate, thus failed to confirm the Mont Blanc result. The dashed line is the expected background rate. 

Low-level counting of y-ray emitters using solid scintillation counters is an extensively used technique. The most important aspect of low-level solid scintillation counting is to decrease the counter background. Typical contributions to a solid scintillation counter s background rate from various sources are shown in Table 19.3. 

Here four factors are seen as the major contributors to the detector background rate. They are (a) the cosmic ray shield, (b) the atmosphere surrounding the detector, (c) the detector itself, and (d) the cosmic rays. For the cosmic ray shield about the detector, it is advisable to use old or virgin lead, that is, lead that was purified over 100 years ago, thus allowing any 210Pb present to decay. One should expect 1 cpm/g shield material. Iron can also be used in constructing the detector... 

Since post-treatment amenorrhea of more than 6 months duration was first suggested as an adverse reaction in around 1965, much work has been devoted to delineating the risk and prognosis of menstrual changes after the withdrawal of hormonal contraception. It is now recognized that post-treatment amenorrhea occurs in 0.7-0.8% of women, but this is no different from the background rate of spontaneous secondary amenorrhea. No cause and effect relation between oral contraceptive use and subsequent amenorrhea has been documented. 

Of 34 women who conceived while receiving triptorehn acetate for infertility, five developed gestational diabetes (17%) compared with a background rate of 5% (83). The increased incidence could not be explained by obesity, as only one of these five women had a BMI over 35 kg/m2 nor could it be explained by polycystic ovary syndrome. Larger studies are required to confirm this finding. 

All cases of acute liver failure related to the use of lovastatin have been reviewed, and probably the frequency is similar to the background rate. This suggests that periodic monitoring of alanine transaminase in these patients would be burdensome and expensive (24). 

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