Mean photon flux density

Microalgae can also be grown continuously meaning that the microalgal culture is continuously harvested and the liquid volume removed is continuously replaced with fresh water with nutrients. In the case of chemostat operation the dilution rate is fixed. Assuming a constant photon flux density a steady state will be reached where the biomass concentration does not change anymore and is constant. The influent, water with nutrients, usually does not contain any microalgae. Furthermore, the liquid voltune is usually maintained constant, so Tm = Tout=fr- Finally, it wiU be assumed that the liquid inside the photobioreactor is perfectly mixed, so C om = Cx. Then the biomass balance over the photobioreactor can be simplified as follows ... 

Figure 2. Changes in the rate of photosynthesis expressed on a leaf area basis (column A) and unit chlorophyll basis (column B) as a function of photon flux density for control ( Q ) smd mildewed ( ) leaves on days 1,5 and 9 after inoculation. Standard errors of the means of three determinations are given for each photon flux density.

Fig. 2. Photosystem 2 electron transport from water to phenylene diamine as a function of photon flux density for thylakoids isolated from leaves exposed to control (A), chill in high light (B) and chill in low light (C> treatments. Rates are given for non-phosphorylated (O) and phosphorylated ( > thylakoids. Each point represents the mean of 4 replicates.

Calibration to absolute intensity means that the scattered intensity is normalized with respect to both the photon flux in the primary beam and the irradiated volume V. Thereafter the scattering intensity is either expressed in terms of electron density or in terms of a scattering length density. Both definitions are related to each other by Compton s classical electron radius. 

In a HeNe laser the stationary population density of the upper laser level is Ni 2 lO cm . With Aik = 10 the number of fluorescence photons is 10 s cm, which are emitted into 3 x 10 modes. Into each mode a photon flux = 3 x 10 photons/s is emitted, which corresponds to a mean photon density of (rtph) = < /c < 10" in one mode. This has to be compared with 10 photons per mode due to induced emission inside the resonator at a laser output power of 1 mW through a mirror with R = 0.99. 

Here, n is the number of atoms of this type per volume, is the inelastic mean free path and represents the depth of the region from which the elastic line can be observed", A is the surface area covered by both the radiation and the photoelectron detector,/hv is the incoming flux density of photons of energy hv, and the subscripts i and f refer to the initial and final states of excited electrons, respectively. This equation neither accounts for the size of the angular acceptance cone of the electron analyzer nor for the angular intensity variations due to the emission process or photoelectron diffraction effects (Section 3.2.23.4). Since electron spectrometers usually accept only a small emission cone of sohd angle it is often more... 

This approximation is valid for the cases that optical thickness is very greater than unity. For example when we have a high density and/or high thickness fibrous insulation we may use this approximation. In this case characteristic length is so greater than mean free path of photons and every element of medium is only affected by neighboring elements. So the radiation problem leads to the diffusion one and radiative heat flux will be obtained from Eq. 13.4 [7] ... 

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