Hemispherical mirror

Figure 1-6 illustrates the mean zonal wind field for the northern hemisphere. The situation in the southern hemisphere mirrors that of the northern, although not quantitatively. In midlatitudes the dominant wind direction is from west to east, with maximum velocities in the vicinity of the subtropical jet stream near 30° latitude. The location of the polar jet stream associated with the polar front is more diffuse, and it does not show up in the averaged wind field. The westerlies encircle the globe in a wave-like... 

The measurement is carried out in an UHV chamber. Ultraviolet photons from a He lamp (21.2 or 40.8 eV) are shone at the sample to eject photoelectrons. The emitted electrons are collected by an electron energy analyser, such as a hemispherical mirror analyser, to produce a spectrum showing the number of electrons emitted with a given kinetic energy. Such spectra are representative of, although not identical to, the sample s valence band electronic density of states (DOS). 

The use of hemispherical mirrors for measuring directional/hemispherical reflectance predates the use of integrating spheres for the same purpose by a few years. Paschen (11) placed lamp and platinum black-coated detectors at the center of a hemispherical mirror in order to enhance the detector s absorptance and used this arrangement to determine the constants in Wien s radiation law. Royds (12) positioned a sample and detector at the conjugate foci of a hemispherical mirror in order to measure the reflectance of blackened thermal detectors. In the acknowledgments of a 1911 paper... 

The maximum linear magnification of a hemispherical mirror along the axis containing the detector/source and sample is approximately given (25) by... 

Clarke and Larkin (59) have modified a hemispherical mirror reflectometer operated in the 2re/0 mode so that the source can be viewed with and without the sample present. By ratioing these two measurements, they determine the factor by which the sample reflectance is enhanced due to interreflections. Clarke and Larkin then measure the sample reflected power and the source power passing through the sample aperture, using optics... 

Fig. 7. Normalized throughput of a dual-paraboloid, hemiellipsoid, and hemispherical mirror reflectoraeter versus the sample position.

The encircling probe was characterised with its mirror in water. As we did not own very tiny hydrophone, we used a reflector with hemispherical tip with a radius of curvature of 2 mm (see figure 3c). As a result, it was possible to monitor the beam at the tube entrance and to measure the position of the beam at the desired angle relatively to the angular 0° position. A few acoustic apertures were verified. They were selected on an homogeneous criteria a good one with less than 2 dB of relative sensitivity variations, medium one would be 4 dB and a bad one with more than 6 dB. 

These modes of operation ate used in conjunction with the two most popular energy analyzers, the cylindrical mirror analyzer (CMA) and the concentric hemispherical analyzer (CHA). The most common form of the CMA used today is the double-pass version diagramed in Eigute 21. This device consists of two perfectly coaxial cylinders of radii r and r. The outer cylinder is held at a potential of (— ) and the inner cylinder is held at ground. The... 

If the spherical anode is situated at a finite depth, f, the resistance is higher than for t and lower than for t = 0 (hemisphere at the surface of the electrolyte). Its value is obtained by the mirror image of the anode at the surface (f = 0), so that the sectional view gives an equipotential line distribution similar to that shown in Fig. 24-4 for the current distribution around a pipeline. This remains unchanged if the upper half is removed (i.e., only the half space is considered). 

Fig. 7-4 Cross-section of the northern hemisphere atmosphere showing first-order circulation. The southern hemisphere is a mirror image.

Figure 2.24 A human subject with a cut corpus callosum views a color Mondrian. Half of the color Mondrian is covered with black velvet. A purple test region is located at the center of the stimulus. The left half of the stimulus is processed by the right hemisphere of the brain and vice versa. The subject views the stimulus either directly or through a mirror. (Adapted by permission from Macmillan Publishers Ltd Nature, E. H. Land, D. H. Hubei, M. S. Livingstone, S. Hollis Perry, M. M. Burns, Nature, Vol. 303, No. 5918, pp. 616-618, Copyright 1983. Figure 2.24 shows the visual path (Figure 2.9) which is reproduced from Semir Zeki. A Vision of the Brain. Blackwell Science, Oxford, 1993, by permission from Blackwell Science Ltd.)...

A normal observer is able to exchange information between the left and the right hemisphere of the brain through the corpus callosum. A normal observer is therefore able to report on the correct color of the test region if the neutral-density filters are not used. In contrast, the subject with a cut corpus callosum can only report on the visual information processed by the left hemisphere of the brain. His color perception depends on whether a mirror setup is used. Therefore, the visual cortex is also involved in the process of color constancy. 

Higher resolution is offered by dispersive analysers of which the main types are the 127° (27), the hemispherical (28), and the cylindrical mirror analyser (29). The various types will not be discussed here and the reader is referred to the useful summaries by Eland (4) and Sevier (30). At least two commercial companies offer uhv photoelectron spectrometers for surface work combining hemispherical analysers with discharge lamps. Bradshaw and Menzel describe (25) a system for surface studies, whereby other techniques can be combined with photoelectron spectroscopy (see Fig. 3). 

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