Density filters, variable

To evaluate the quantity of interest, i.e., the relative change in reflectance, AR/R, a normalization procedure must be used to eliminate the uninteresting common feature /q(X). In Figure 2 the normalization is performed by the variable neutral density filter (VNDF) connected to a servo mechanism. The dc signal from the detector, which is proportional to /o(A.)./2(A.), is introduced into the servo, which moves the VNDF in such a manner as to keep /Q(k)R(k) constant, i.e., /q(X)R(X) = C. Under these conditions the ac signal Iq(X)ARQC) = CARQC)/RQC. ... 

Photochromic or phototropic dye stuffs are used as the basis of photochemical high speed memory with an erasable image. They can also be used as automatic variable density filters for example as Q-switches in high intensity lasers. For thermochromic substances colour change is observed on change of temperature (spirans, bianthrones). 

The densitometer uses a two beam comparator technique of measurement. A single lamp illuminates, through a variable neutral density filter, the emitter of an eleven stage photomultiplier tube. Because the frequency of measurement is five times the AC line frequency and the amplifiers are extremely high gain, the lamp must be operated from a regulated DC source, otherwise, 120 Hz brightness ripple of the lamp is recorded in the data. 

The t q)ieal optical setup of a fluorescence-lifetime spectrometer is shown in Fig. 5.5. The sample is exeited by a laser. The excitation intensity is adjusted by a variable neutral density filter. An additional bandpass filter may be required to bloek unwanted emission wavelengths of the laser. 

Four PMTs detect the transmitted light under different projection angels. The four detector signals are connected to the individual channels of a four-module TCSPC system. In practice, variable neutral-density filters and long-pass filters are placed in front of the detectors to compensate for different intensity at different breast thickness and to reduce the daylight sensitivity. 

The experimental high pressure process provides cw power up to 270 mW. The beam from a one watt, TEMoo mode, cw Nd-YAG laser (emission wavelength 1.064 m) is passed through a polarizer, a Linconix laser power stabilizer, a variable neutral density filter, a beam expander, and focused with a 10 cm focal length lens into the fiber growth reactor [2] [12]. Laser power ranges from 0 to 200 mW with a stability of one mW, as measured outside the reaction chamber. 

Some commonly filters used in LES are the cut-off, box, and Gaussian. For flows with density, p, variable, the Favre filter is given by... 

Photochromic lenses for eyewear serve as variable density optical filters. Other appHcations for photochromic light filters have been proposed including gla2ing appHcations for solar attenuation, variable transmission camera lenses, and shields for protection against the light flash from a nuclear explosion. 

Times less than 1.5 seconds (for example, 1 second, 0.5 second, 0.25 second) may lead to inconsistent results because of variables in lamp warmup. Use neutral density (ND) filters to adjust the El as necessary and allow for longer exposure times. 

The filtered quantity / is resolved in the numerical simulation whereas / = / — / is the subgrid scale part due to the unresolved flow motion. For variable density p, a mass-weighted Favre filtering is introduced so that ... 

Nucleopore filters from the same lot should be used throughout the experiments. While pore diameter is uniform, there might be considerable variability in pore density. Therefore, filters should be checked before use by passing a certain amount of medium (20-50 ml), and measuring the time it takes to pass through this is proportional to the total pore area. Only filters giving similar flow values should be used in the experiments. 

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