Variable aperture

This meter may thus be considered as an orifice meter with a variable aperture, and the formulae already derived are therefore applicable with only minor changes. Both in the orifice-type meter and in the rotameter the pressure drop arises from the conversion of pressure energy to kinetic energy and from frictional losses which are accounted for in the coefficient of discharge. The pressure difference over the float —AP. is given by ... 

Figure 5.15 shows a ray diagram for a light-optical projection microscope. The light source is placed behind a condenser system which collects the light which is diverging from the source and illuminates the specimen. The presence of the variable aperture near to the condenser lens permits control of the area of the specimen which is... 

The width and length (height) of the slit is adjustable by a variable aperture. The slit can be optically imaged on the plate. If sample spots are poorly separated, a small slitwidth is chosen this enables the spots to be measured separately. In some instruments the band-width of the monochromatic light is actually determined by the slit-width, and thus, in order to maintain good optical resolution the latter should be kept small. 

Tsang, Y.W., C.F. Tsang, I. Neretnieks, and L. Moreno. 1988. Flow and tracer transport in fractured media a variable aperture channel model and its properties. Water Resour. Res. 24 2049-2060. 

Observations of flow distribution in natural fractures show stream widths varying between cm and tens of cm (Abelin et al. 1991,1994). Measurements of aperture variations indicate correlation lengths in this range (Hakami and Larsson 1996). Simulations of flow in variable aperture fractures also suggest that stream widths from cm to tens of cm can be expected in fractured granitic rocks. 

As mentioned earlier, it is not likely that the entire spectral region would be included in a single spectrum. Instead, optical filters are used to restrict the spectral region. In order to optimize the overall system performance, it is desirable to match the angular field-of-view to the selected spectral region. This can be done by inserting a variable aperture at a field-stop in the optical... 

Rotating sector disks also are frequently used in emission spectroscopy. The three principal types of rotating sectors are shown in Figure 5-5. The sector disk, illustrated in Figure 5-5A, has a variable aperture and is used to reduce the intensity of exposure. The sector disk is mounted in the optical path in front of the entrance slit to the spectrometer and is rotated at a constant rate. 

The Pritchard optical system allows the operator to simultaneously view and measure the brightness and color of small target samples through a variable magnification and variable aperture photometer (40) (Fig. 6). Each of these instruments measures a specimen s color in one limited way. These data, in turn, are only one dimension of the specimen s appearance (41) (See Fig. 7). 

Figure 2 - One concept of the infrared radiometer layout is shown. The photometer contains a dewar with a one-year lifetime, the chopper for removing the background offset, two detectors and a set of variable apertures and filters for each.

The vapor pressure gradient is solely a physical property depending upon environmental factors. In contrast, the stomata with variable apertures respond to plant parameters as well. 

FuentesNO, Faybishenko BA. (2002) RIMAPS characterization of surface in the variable aperture model and determination of the main paths for water flow. Proc XXIXAnnual Meeting ofAATN, Buenos Aires, Argentina, 036 1—8. 

A, sedimentation tank B, stirrer C, collimator D, light proof box E, variable aperture G, lenses K, drive screw L, light source M, motor Mi,... 

In any image-forming system such as the optics of an FT-IR spectrometer, the optical throughput (see Section 2.7) of the beam is fixed by two limiting apertures, the entrance pupil and the field stop. The aperture stop limits the diameter of the beam at each optical component, while the field stop determines the size and shape of the image. In an FT-IR spectrometer, the aperture stop is usually decided by the diameter of the beamsplitter or one of the larger mirrors in the optical path. However, in one instrument, a variable aperture, called the beamplitter stop or... 

Forensic analysis of fibres constitutes another major application of infrared spectroscopy. The spherical structure of fibres makes it necessary to flatten the sample before measuring its spectrum, for which it is possible to use either a roller or a diamond cell. Once the fibre is prepared, the variable apertures of the microscope allow the masks to be adapted to the size of the fibre. 

A typical IR microscope is all-reflecting, with visible illumination for visual examination of the sample and with a dedicated on-axis small area mercury-cadmium telluride (MCT) detector. The sampling size can vary from less than 50 x 50 p.m in linear dimensions to the dimensions of the detector element. The sample is placed on a standard microscope X-Y stage and can be visually examined under a variety of magnifications. The sample area of interest is isolated by placing a variable aperture on an intermediate image of the sample within the barrel of the microscope. 

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