Planetary

Isaac Newton modestly claimed to have stood on the shoulders of giants to explain how he was able to achieve his outstanding discoveries in the fields of gravitational attraction and planetary motion our Giants in the field of electromagnetic induction would probably have said the same. 

The miderstanding of the quantum mechanics of atoms was pioneered by Bohr, in his theory of the hydrogen atom. This combined the classical ideas on planetary motion—applicable to the atom because of the fomial similarity of tlie gravitational potential to tlie Coulomb potential between an electron and nucleus—with the quantum ideas that had recently been introduced by Planck and Einstein. This led eventually to the fomial theory of quaiitum mechanics, first discovered by Heisenberg, and most conveniently expressed by Schrodinger in the wave equation that bears his name. 

In fact, even in the solar system, despite the relative strengths of planetary attraction, there are constituents, the asteroids, with very irregular, chaotic behaviour. The issue of chaotic motion in molecules is an issue that will appear later with great salience.)... 

The astrochemistty of ions may be divided into topics of interstellar clouds, stellar atmospheres, planetary atmospheres and comets. There are many areas of astrophysics (stars, planetary nebulae, novae, supemovae) where highly ionized species are important, but beyond the scope of ion chemistry . (Still, molecules, including H2O, are observed in solar spectra [155] and a surprise in the study of Supernova 1987A was the identification of molecular species, CO, SiO and possibly ITf[156. 157]. ) In the early universe, after expansion had cooled matter to the point that molecules could fonn, the small fraction of positive and negative ions that remained was crucial to the fomiation of molecules, for example [156]... 

For remote sensing, spectroscopy at THz frequencies holds the key to our ability to remotely sense enviromnents as diverse as primaeval galaxies, star and planet-fonuing molecular cloud cores, comets and planetary atmospheres. 

Nellis W J, Flamilton D C, Flolmes N C, Radousky FI B, Ree F FI, Mitohell A C and Niool M 1988 The nature of the interior of Uranus based on studies of planetary ioes at high dynamio pressure Science 240 779... 

Anoilotto F, Chiarotti G L, Soandolo S and Tosatti E 1997 Dissooiation of methane into hydrooarbons at extreme (planetary) pressure and temperature Science 275 1288... 

Hubbard WB 1984 Planetary Interiors (New York Van Nostrand-Reinhold)... 

Bauer S J 1973 Physics of Planetary Ionospheres (Berlin Springer)... 

S. R. Taylor, Planetary Science A. PunarPerspective, Lunar and Planetary Institute, Houston, Tex., 1982. 

Assemblies of small disks are rotated in a planetary movement around a central screw conveyor. The disks are mounted on six hoUow axles and the axles revolve on overhanging bearings from the gearbox at one end of the vessel where they are driven, via a drive shaft, by an electric motor. The filtrate is collected from the disks via the hoUow shafts and a filter valve into a large collecting pipe. The hoUow shafts also collect the water and air from the dewatering process, in another part of the rotational cycle. The number of disks mounted on the shafts can be adjusted for different materials, depending on the required capacity and the cake thickness to be used. 

As the vessel is only about half filled with slurry, the disks become coated with the cake when immersed, the cake is dewatered when the disks emerge from the slurry, and scraped or blown off, by reverse blow, into the central conveyor which takes the cake to one end of the vessel. The planetary action and the slow movement of the disks through the feed slurry ensure exceptionally good homogeneity of the cake which is critically important for good dewatering characteristics the typical speed of rotation of the planetary system of shafts is from 0.8 to 1 rpm. 

Fig. 3. Schematic of three commonly used types of MOCVD reactors where the arrows indicate gas flow (a) vertical rotating disk where (— represents an inlet to promote a laterally uniform gas flow, (b) planetary rotation, and (c) hori2ontal.

Twin shell Vibratory pehhle mill tiirretf Vertical screw planetary types Cage mill Screw feeders... 

Planetary Ball Milling This is a method of increasing the gravitational force acting on balls in a ball mill. For example, refractoiy metals and carbides can be ground to 1 to 2.6 [Lm in 5 to 20 min in an apparatus capable of applying a centrifugal force of 10 to 50 G. [Dobrovol sldi, Poroshk. MetalL, 7(6), 1-7 (1967)]. 

Pulverit planetaiy mills are available from Geoscience Inc. Highspeed planetary-baU mills can be used to perform rapid tests to sinmlate ball milhng of materials [Vock, DECHEMA-Monogr, 69, HI-8 (1972)]. The size of high-speed mills will be much smaller than the size of same-capacity ball mills [Bradley, S. Afr Mech. Eng., 22, 129 (1972)]. 

Batch planetary mixers are used extensively in the pharmaceutical industiy for powder granulation. A typical batch size of 100 to 200 kg has a power input of 10 to 20 kW. Mixing times in these granulators are quite long (20 to 40 min). 

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