Optical density external

The optical density (OD) of the sample was varied by repeatedly diluting the mixture with fresh gas until a value of roughly 0.8-1.2 was obtained in some cases, scans were acquired with ODs as low as 0.1. Absorbance measurements were made directly in the cell using a Mattson Research Series FT-IR spectrometer (0.25 cm1 resolution) configured for external beam operation. The optical layout makes it possible to easily switch from making ps pump-probe measurements to recording an IR spectrum. 

Figure 2 C. thermoaceticum cultures were grown at 60°C with glucose (56 mM). COj was bubbled through the medium to maintain an anaerobic environment and as an external electron acceptor. Optical density ( ), pH ( ), glucose (A), acetate (T), and FDH specific activity ( ) were assayed as in [19].

Gottmann, K. C.J. Weijer. 1986. In situ measurements of external pH and optical density oscillations in Dictyostelium discoideum aggregates. J. Cell Biol. 102 1623-9. 

The elements of the molar extinction coefficient tensor are defined in the solute molecular fixed axes system, whereas the polarization direction of the absorbed and the emitted light is defined in the space-fixed axes system (U, V, W Ui, U2, U3). The optical density at the wavelength X for light polarized parallel to an external axis Uj is given by... 

---