Logarithmic amplification

Analyze the FITC (FL1) and PE (FL2) signals using logarithmic amplification. Ensure that the majority of the gated cells are positive for FITC and negative for PE (Fig IB). 

Fig. 3.9. The effect of changes in the photomultiplier tube voltage and amplifier gain on the appearance of six signals with intensities in the relationship of 1 2 10 20 100 200 to each other. A Linear amplification. B Logarithmic amplification, (continued on next page)...

Log amplifiers are usually employed to analyze fluorescence signals from cells with stained surface markers, because these cells often exhibit a great range of fluorescence intensities. Linear amplifiers are usually employed for analyzing the DNA content of cells, because the DNA content of cells does not normally vary by more than a factor of 2 (e.g., during cell division). Linear amplifiers may be used to analyze forward and side scatter signals, but practice here is apt to vary from lab to lab. With either linear or logarithmic amplification,... 

Fig. 3.11. Intensity signals from fluorescent beads (of five different intensities) acquired with linear amplification (top) and logarithmic amplification (bottom). Log amplification permits all five intensities to be on scale (that is, within the 1024 channel range). Additionally, the spread (the CY) and the peak height of the distributions for each bead are visually similar with a log but not with a linear amplifier. From Givan (2001).

Figure 3-6 Discriminator settings for simultaneous detection of 5H and, 4C in linear amplification (e.g., Packard Inst.) at left, and logarithmic amplification (e.g., Beckman), at right.

All measurements were carried out in the tritium and/or the carbon-14 channel with linear (not logarithmic) amplification. 

Fig. 43. Ion meter with digital activity or concentration display, logarithmic amplification, isotherm intersection point adjustment and option for two high ohmic inputs (Metrohm)...

For every decade of input, the output changes about 120 mV. In commercial logarithmic amplifiers, a subsequent linear amplification stage further amplifies the output voltage to a preset value. A typical input-output characteristic of a commercial logarithmic amplifier is shown in Fig. 11.4. 

Ratios of power in electronic circuits are measured in decibels. A hypothetical unit of a Bel would describe the logarithm to base 10 of the ratio of two power levels the decibel (dB) is a unit of a tenth of a Bel. Hence the ratio of two power levels Pi and P2 may be described as a = 10 x log10(P[/P2) dB. Conversely, Pi = P2 x 10 /10. The decibel is dimensionless and, since it is a logarithmic unit, amplifications and attenuations expressed in decibels can... 

Fig. 1. Analysis of fluospheres (Dako Ltd.) using logarithmic (open peaks) and linear (filled peaks) amplification. Logarithmically amplified peaks are identified by upper-case letters, and the corresponding bead peak amplified on a linear scale by lower-case letters. The linear scale discriminates between bright signals (for example, d and e) better than the log scale (D and E). but the range of fluorescence covered by the log scale is much greater than the linear scale.

Time course of rDNA amplification in the Xenopus laevis oocyte. The amount of rDNA per cell is plotted against time. Note that the ordinate is a logarithmic scale. The sharp drop in rDNA at fertilization is thought to be due to dilution of the amplified rDNA copies by cell division, rather than to their destruction. (From A. P. 

Thus, to a first approximation, the gas amplification depends exponentially upon the number of charge per unit length of anode wire, the logarithmic term being of less influence. 

Due to the wide variation in cellular contents of mitochondria, it is advisable to use logarithmic signal amplification for the signal channels collecting mito-chondria-related fluorescence. Carefully resuspend the cell sample by gently pipetting up and down a few times immediately before analysis. 

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