Common earths

Cerium was the first rare-earth element discovered, and its discovery came in 1803 by Jons Jakob Berzelius in Vienna. Johann Gadohn (1760—1852) also studied some minerals that were different from others known at that time. Because they were different from the common earth elements but were all very similar to each other, he named them rare-earth elements. However, he was unable to separate or identify them. In the 1800s only two rare-earths were known. At that time, they were known as yttria and ceria. Carl Gustav Mosander (1797—1858) and several other scientists attempted to separate the impurities in these two elements. In 1839 Mosander treated cerium nitrate with dilute nitric acid, which yielded a new rare-earth oxide he called lanthanum. Mosander is credited with its discovery. This caused a change in the periodic table because the separation produced two new elements. Mosander s method for separating rare-earths from a common mineral or from each other led other chemists to use... 

In the common earth will sleep our rotten rest ... 

The name rare earths is a misnomer since these elements are neither rare nor earths. The name rare earths referring to elements with atomic numbers 58 to 71 may have arisen because they were initially isolated as oxides which, in some ways, resemble calcium, magnesium and aluminum oxides known as common earths. A chronological summary of the discovery of the elements is given in Table 1.1. 

I.2.I. Systems with common earth alkali metal halide... 

From the above considerations it can be concluded that the slopes of the X versus 812 plots for the common earth alkali halide systems should increase in the sequence Mg < Ca < Sr < Ba. This was indeed experimentally observed. Except for the lithium halide-earth alkali metal halide systems, the data are well represented by the X versus 512 plot for each common earth alkali metal halide system. The slopes of X versus 5i2 plot increase when the radius of the common earth alkali metal cation is increasing. 

This method is commonly used in the oil industry because of the predominance of steelwork in a typical installation. In this method the power system is earthed separately from the equipment frames and cnbicles. The star point at the sonrce is the only common earthing point. The lEG standard reqnires the circuit to be protected by a residual earth fault current device at the switchboard or motor control centre, where the consumer is located in a Zone 1 area. 

Re is the resistance of the common earth path of the signal cable. 

Assume that the screen is earthed at both ends at the same points as the signal source and the output load. Hence the common earth resistance Re is shared by both the screen and the core circuits. Again assume that Fin is zero for the same reason as above. 

The first of the rare earths, yttrium, was discovered just before the beginning of the Nineteenth Century (1794) in a rare Swedish ore, and separated in the form of an impure oxide. At that time, the more active metals such as magnesium, calcium, aluminum and barium had been isolated only in their oxide form. These oxides were believed to be elements and were referred to as common earths . The ancient Greeks taught that all matter was made up of... 

In this figure, both SPDs located at two zones have earth bus systems, which are connected alternatively each of them could be connected separately by earthing bus bar or conductor to a common earthing bus (as optional shown). In case of conductor connection it shall be at least 8 AWG to offer minimum resistance as... 

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