Seven Basic Units

Units), with the international abbreviation SI, was adopted for this modernized metric system. Further improvements in and additions to SI were made by the General Conference in 1964, 1968, and 1971. 

Temperature—Kelvin (K) The Kelvin is defined as the fraction 1 /273.16 of the thermodynamic temperature of the triple point of water. The temperature 0 K is called absolute zero. On the commonly used Celsius temperature scale, water at atmospheric pressure freezes at about 0°C and boUs at about 100°C. The °C is defined as an interval of 1 K, and the Celsius temperature 0°C is defined as defined as 273.15 K. 1.8 Fahrenheit scale degrees are equal to 1.0°C or 1.0 K the Fahrenheit scale uses 32°F as a temperature corresponding to 0°C. 

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Except for temperature and time, nearly all scientific measurements are based on the metric system. In recent years, there has been a concerted international effort to persuade scientists to express all metric measurements in terms ofjust seven basic units, called SI units (for Systeme International). In addition to the seven basic SI units, there are seventeen other common units derived from them that have special names. However, despite the logical arguments that have been put forth for undeviating adherence to SI units, there has not been a strong popular move in this direction. For one thing, each scientist must cope... 

SI (Systeme International, International System of Units)—metric-based system of weights and measures adopted in 1960 by the 11th General Conference on Weights and Measures, in which 36 countries, including the U.S., participated. SI consists of seven basic units ... 

The basic design of the devices used to develop an ASE process as reported in the first study using the Dionex" ASE 200 extractor [2,3], and also in some later investigations conducted using laboratory-built systems [1,18,77], is shown in Fig. 6.4. As can be seen, the equipment required to implement ASE consists of seven basic units, namely ... 

In the SI system the seven basic units fisted in Table 1.2-1 are identified and their values are assigned. From these seven basic well-defined units, the units of other quan-dties can be derived. Also, certain quantities appear so frequently that they have been given special names and symbols in the SI system. Those of interest here are listed in Table 1.2-2. Some other derived units acceptable in the SI system are given in Table 1.2-3, and Table 1.2-4 lists the acceptable scaling prefi.xes. [It should be pointed out... 

The International System of Units (Systeme International SI) was adopted in 1960 by the General Conference of Weights and Measures as a coherent system based on seven basic units the meter, kilogram, second, ampere, kelvin, candela, and mole. In human medicine, the system has not been adopted universally. 

For historical reasons a number of different units of measurement have evolved to express a quantity of the same thing. In the 1960s, many international scientific bodies recommended the standardisation of names and symbols and the adoption universally of a coherent set of units — the SI units (Syst me Internationale d Unitds) — based on the definition of seven basic units, namely metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd). 

The International System (Le Systeme international d Unites) was established in 1960 (11th CGPM, Conference G6nerale des Poids et Mesures). There are seven basic units that are given in Table 11.2. The definition of the units was revised from time to time. For instance, originally the unit of length was given as 1 /(40 x 10 ) of... 

From the basic units, other units may be derived, e.g., Newton, Pascal, Joule, Volt To the basic units prefixes may be attached. The prefixes are given in Table 11.4. We ask now whether the seven basic units are literally basic. For example, we can derive the temperature from the ideal gas law... 

In fact, the question arises whether we need really these seven basic units, or whether the number of basic units can be still fiuther reduced. For example, around 1900, Oswald suggested that the energy should be one of the basic units. Instead... 

The SI might be useful from the point of view of technology and metrology, but from the point of view of pure physics four out of its seven basic units are evidently derivative ones. 

A unit cell is the basic repeating structural unit of a crystalline solid. Figure 6.11 shows a unit cell and its extension in three dimensions. Each vertex in Figure 6.11 represents a lattice point. In a crystal lattice, every lattice point has an identical environment. In simple crystals, such as metals, the lattice point is occupied by an atom. For more complex crystals, however, there may be several atoms, molecules, or ions arranged around each lattice point. There are only seven basic unit cell shapes crystal systems) that can be used to form a crystalline solid (Figure 6.12). 

More than three hundred distinct units of measurement have heen defined in the British Imperial and U.S. customary systems of measurement hut only seven in the metric system. All other metric units are either multiples of ten or comhrna-tions of these seven basic units. 

The International System of Units (SI) is the modem metric system of measurement. The abbreviation SI is derived from the French Le Systeme International d UniUs. The ll" General Conference on Weights and Measures (CGPM, Confirmee Ginirale des Poids et Mesures) estabhshed the system in 1960. The seven basic units in the SI system are shown in Table 1.2, the recommended prefixes in Table 1.3 and derived units of general character are shown in Table 1.4. Some constants of importance for this book are collected in Table 1.5. These tables are collected at the end of this chapter (see pp. 14ff.). 

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