Micro, SI prefix

One advantage of any metric system is that it is a decimal system. In SI, a larger or smaller unit for a physical quantity is indicated by an SI prefix, which is a prefix used in the International System to indicate a power of ten. For example, the base unit of length in SI is the meter (somewhat longer than a yard), and 10 meter is called a centi-meter. Thus 2.54 centimeters equals 2.54 X 10 meters. The SI prefixes are fisted in Table 1.3. Only the highlighted ones will be used in this book mega- (10 ), kilo- (10 ), deci- (10 ), centi- (10 ), milli- (10 ), micro- (10 ), nano- (10 ), andpico- (10 ). 

A new classification of pore sizes is proposed. It is based on prefixes defined by the Bureau International des Poids et Mesures under Le Systeme International d Unit s (SI) [1] (in particular nano-, micro- and milli-), unlike the current classification scheme defined by the International Union of Pure and Applied Chemistry (lUPAC) [2]. Thus the new classification is also consistent with other common scientific terms based on SI prefixes such as nanotechnology [3]. Further advantages are that unlike the lUPAC scheme - which is derived from physical adsorption phenomena in pores narrower than 50 nm - the new classification is entirely decoupled from any physieo-ehemieal system or process and is not biased towards small pores. However, the proposed new scheme is more complicated than the current lUPAC one, especially regarding suh-divisions of the main pore size classes. Also, the term micropore occurs in both schemes, which makes them incompatihle, at least over the micropore size range as defined in the new classification. 

In trace analysis, the units used for component content should be appropriate for the amount. The most proper system is to give the mass fraction (wb) of the trace component (B) in SI units with the appropriate prefix milli- (10 ), micro- (10 ), nano- (10 ), pico- femto- (10 ), or atto- (Table 1.1). The... 

The defining event of a radioactive nuclide is the transformation of its nucleus into the nucleus of another species, that is, radioactive decay. The number of nuclear transformations occurring per unit of time is called activity . Sometimes radioactivity is used instead of activity . The traditional unit of activity has been the Curie (Ci), which is equal to 3.7 X 10 ° nuclear transformations per second. The conversion of radiation units to the international system (Sysfme International d Unit or SI) has now taken place in the United States. The more fundamental unit of activity, the Becquerel (Bq), equal to 1 nuclear transformation per second, has replaced the Curie. Both units of activity are modified by prefixes such as kilo-, milli-, and micro- to achieve standard multiples of the fundamental unit. A listing of the most commonly used prefixes is given in Table 1. 

Volume val-y9m [ME, fr. ME, fr. L volumen roll, scroll, fr. volvere to roll] (14c) n. The space occupied by an article or sample of material, including any voids, within the defining surfaces. The SI unit of volume is the cubic meter, m, known in the past by the name stere, now deprecated (but alive and well in crossword puzzles). SI also allows the use of convenient subvolumes, e.g., m, cm. The exponent also operates on the abbreviated prefix in each case [i.e., lcm = lcm = 10 m, not 0.01 m ]. The special name litre (liter in the US English) has been approved for the cubic decimeter (dm ) but is to be used only for volumetric capacity and dry and liquid measure. No prefix other than milli- (m) or micro- (p) should be used with liter. Some conversions of other volume units to SI are given in the Appendix. 

The second (s) is the SI base unit of time (Figure 1.22). Combining this unit with prefixes such as milli-, micro-, nano-, and pico-, you create units appropriate for measuring very rapid events. The time required for the fastest chemical processes is about a picosecond, which is on the order of how fast supercomputers can perform a single calculation. When you measure times much longer than a few hundred seconds, you revert to minutes and hours, an obvious exception to the prefix-base format of the International System. 

The special feature of the SI as well as the metric system is that a prefix can be placed in front of any unit to increase or decrease its size by some factor of 10. For example, the prefixes milli and micro are used to make the smaller units, milligram (mg) and microgram (/tg). Table 2.4 lists some of the metric prefixes, their symbols, and their numerical values. 

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