Background illumination

Constant deviation spectrophotometer 80 W tungsten lamp [VI, [Bl, [Of [LDn] [L-ns]. Double light trap3. Red background illumination. Visual evaluation Mast64)... 

Adjust the temperature of the heat tube bath to 82.2il°C and insert all four test tubes info thc hvStirig sci i Xhc cj pch of iiorn rsicn. should be approx 2 inches. Place the bath tn such a position diat the test tubes are viewed against a white background illuminated by bright diffused daylight. Note die time of insertion of the tubes into the bath. 

Figure 2.8 Light- and dark-adapted intensity-response curves recorded intracellularly from a red cone of turtle retina. The dark-adapted potential is 0 mV. This shift of the response curve enables the visual system to discriminate small increments or decrements about the background level. (Reproduced from R. A. Normann and I. Perlman. The effects of background illumination on the photoresponses of red and green cones. Journal of Physiology, Vol. 286, pp. 491-507, 1979, by permission of Blackwell Publishing, UK.)...

Figure 6.1 Two sample images. The scene in (a) shows a table illuminated by a yellow illuminant. The scene in (b) shows a desk illuminated by sunlight falling through a blue curtain. This creates a blue background illumination. The lamp on the desk was also switched...

Normann RA and Perlman I 1979 The effects of background illumination on the photoresponses of red and green cones. Journal of Physiology 286, 491-507. 

Figure 3.4. Photographs taken with background illumination of sessile drops of pure A1 on polycrystalline alumina in high vacuum at 850°C (top) and 120(PC (bottom). From (Coudurier et al.

Figure 3.5. Video images of sessile drops of two Ni alloys on Ali03 at 1500" C with (left) and without (right) background illumination (Labrousse 1998). On the left image, one can distinguish the reflection of the resistance heater on the droplet as well as the capillary used to dispense the droplet. By tilting slightly the substrate, it is possible to determine accurately the position of the triple line (dashed line) by the intersection of the drop profile and the drop shadow (or reflection) on the substrate surface.

Where R is the reflectivity and d is the thickness. Very accurate values of R and T are needed when the absorptance, (id, is small. The technique of photothermal deflection spectroscopy (PDS) overcomes this problem by measuring the heat absorbed in the film, which is proportional to ad when ad 1. A laser beam passing just above the surface is deflected by the thermal change in refractive index of a liquid in which the sample is immersed. Another sensitive measurement of ad is from the speetral dependence of the photoconductivity. The constant photocurrent method (CPM) uses a background illumination to ensure that the recombination lifetime does not depend on the photon energy and intensity of the illumination. Both techniques are capable of measuring ad down to values of about 10 and provide a very sensitive measure of the absorption coefficient of thin films. 

The development of the experimental procedure then involves the preparation of standard mixtures to prepare a calibration curve, with due care paid to corrections for particle size distribution, background, illuminated volume of sample and preferred orientation. A typical calibration run is shown in Fig. 4.25. Determinations on a series of similar spiked mixtures leads to the calibration curve in Fig. 4.26. Analysis of the resulting data led to the determination of a minimum quantifiable limit of 5 per cent, a working range of 5-50 per cent Form B and an RDS of 16 per cent. The method... 

Fig. 6. Absorbance changes induced by 33-ps, 850-nm laser pulses in Complex 1 obtained from membranes of the green sulfur bacterium Pc. aestuarff. (A) Membrane with "closed RCs (sample containing FeCy and under background Illumination) (B) membrane with open RCs (sample containing Asc and PMS). Solid-line traces represent absorbance changes observed at the time the excitation flash was applied, and the dotted-line traces are for changes observed at 350 ps after the flash. Figure source Shuvalov, Amesz and Duysens (1986) Picosecond spectroscopy of isolated membranes of the photosynthetic green sulfur bacterium Prosthecochloris aestuarii upon selective excitation of the primary electron donor. Biochim Biophys Acta. 851 2, 3.

In 1979, Sauer, Mathis, Acker and van Best and Shuvalov, Dolan and Ke used TSF-I particles, a more intact reaction-center complex, and maintained them at - 0.62 V (with dithionite) plus either neutral red or background illumination in order to trap the iron-sulfur proteins in the reduced state. 

Fig. 5. (A) AA at 694 nm in TSF-I particles poised at 200 mV and excited by 50-ps flashes at 694.3 nm [(trace (a)] and AA measured in TSF-I particles with P700 pre-oxidized by background illumination [trace (b)] (B) AA measured in TSF-I particles poised at -625 mV (note the different scales for the time axes) (C) AA at 694 nm measured in TSF-I particles (a) poised at 200 mV, (b) P700 pre-oxidized by continuous illumination, and (c) heat treated to inactivate the bound iron-sulfur centers (D) AA (red-region) measured in TSF-I particles 150-ps and 800-ps after the flash 30-ps flashes at either 708- or 689-nm were used [see data-point code in the inset) Note the different absorbance scales used. (E) AA (450-600 nm) induced by 30-ps, 689-nm flashes (F) solid trace is the difference between AA measured at 150-ps and 800 ps the dashed trace is the in vitro difference spectrum for Chl-a anion radical, shifted toward the red by -25 nm. Figure source (A) and (B) from Shuvalov, Ke and Dolan (1979) Kinetic and spectral properties of the intermediary eiectron acceptor A, in photosystem I. Subnanosecond spectroscopy. FEBS Lett 100 6 (C)-(F) from Shuvalov, Klevanik, Sharkov, Kryukov and Ke (1979) Picosecond spectroscopy of photosystem I reaction centers. FEBS Lett 107 314, 315.

Fig. 7. Difference spectra of PS-1 particles containing ascorbate and PMS (A) and containing dithionite and PMS plus background illumination to maintain all secondary acceptors chemically reduced (B). Spectral changes induced by 35-ps, 710-nm pulses and recorded 5 ns and 860 ps after the pulse are shown in (A, a) and (A, b), respectively. Spectrum recorded 21 ps after the center of the 35-ps pulse is shown in (A, c) [solid trace]. The dashed trace was similarly measured as the solid trace, except the 35-ps, 710 nm pulse was applied 2 ns after the sample was pre-flashed by a 35-ps, 632-nm pulse. Difference spectra of pre-reduced PS-1 particles induced by 35-ps, 710-nm pulses and recorded 370 ps, 5 ns, and 55 ns after the pulse are shown in (B-a, -b and -c), respectively. The dashed spectrum in (B, a) represents the difference between the solid and dashed traces in (A, c). Difference spectrum for [A --AJ obtained by subtracting the difference spectrum in A, a) from the solid spectrum in (B, a) after normalizing at 700 nm. Figure source Shuvalov, Nuijs, van Gorkom, Smit and Duysens (1986) Picosecond absorbance changes upon selective excitation of the primary electron donor P-700 in photosystem /. Biochim Biophys Acta 850 320-322.

Absorbance changes in the PS-I particle pre-reduced by dithionite/PMS plus background illumination were induced by 35-ps, 710-nm pulses and recorded 310ps and 5 ns after excitation, as shown in Fig. 7... 

Reduced state (sample in glycine buffer at pH 11.5 and containing ascorbate and PMS degassed and then dithionite added to 30 mM background illumination applied to maintain all secondary acceptors reduced, including Aj reduced to the doubly reduced A," state) schematically depicted by 0 in the figures... 

Fig. 44. Plot of l/oj ,in VS. the square of the thickness, d, of the porous GaP film. The IMPS response was measured using modulated illumination from the electrolyte side (A 35 nm) and a constant background illumination level.

The technical specifications of these monitors are impressive they luminesce in the entire visible spectrum, they are bright and efficient. They are thinner and lighter than LCD monitors (liquid crystal displays) and are therefore especially suited for portable equipment. They are intrinsically emissive, and thus require no background illumination, and they have a display angle of nearly 180°. Furthermore, they are fast and thus suitable for rapid video sequences. The image points (pixels) can be switched to a completely dark state, so that higher contrast can be obtained. 

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