The second component of the photocontrol module, a c-di-GMP phosphodiesterase, maintains near-zero background levels of c-di-GMP in the absence of light, which enhances the photodynamic range of c-di-GMP concentrations.
As shown in Figure 1C, wild-type mice exhibited background levels of serum SEAP activity [973 ± 232 relative light unit (RLU), mean ± SE], and it was not increased by TCDD (1,193 ± 307 RLU; Figure 1C).
Luminescence was measured as relative light units (RLU) with an AutoLumat LB 953 luminometer (EG&G Berthold, Gaithersburg, MD). Background levels of luminescence were determined from cells transfected solely with pBluescript SK+, and subtracted, accordingly.
Background levels of genetic alterations.
All behavioral experiments were carried out at the Small Animal Behavior Core facility of the Medical College of Georgia in rooms equipped with white noise generators (San Diego Instruments, San Diego, CA) set to provide a constant background level of 70 dB and ambient lighting of approximately 25 30 Lux (lumen/m2).
The noise level (or background level) of the system is strongly affected by ambient light and also of the gating time of the ICCD camera.
For the low threshold image, the threshold has been set at about the background level of the phantom which is due to e.g. excitation light leakage through the emission filter, fluorescence emission light scatter, and autofluorescence of the phantom [32].
However, it is practically difficult to determine a feasible threshold that gives proper segmentation all over the image because the background level of typical microscopic images is not uniform due to light scattering and non-uniform illumination.
The background level of luciferase activity varied from 700 to 5000 relative light units (RLU) per 5 × 104 cells.
