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silicon

 [sil´ĭ-kon]
a chemical element, atomic number 14, atomic weight 28.086, symbol Si. (See Appendix 6.)
silicon dioxide silica.

SI units

 
the units of measurement generally accepted for all scientific and technical uses; together they make up the International System of Units. (See also metric system.) The abbreviation SI, from the French Système International d'Unités, is used in all languages. There are seven base SI units, defined by specified physical measurements, and two supplementary units. Units are derived for any other physical quantities by multiplication and division of the base and supplementary units. The derived units with special names are shown in the accompanying table.



SI is a coherent system. This means that units are always combined without conversion factors. The derived unit of velocity is the meter per second (m/s); the derived unit of volume is the cubic meter (m3). If you know that pressure is force per unit area, then you know that the SI unit of pressure (the pascal) is the unit of force divided by the unit of area and is therefore equal to 1 newton per square meter.

The metric prefixes can be attached to any unit in order to make a unit of a more convenient size. The symbol for the prefix is attached to the symbol for the unit, e.g., nanometer (nm) = 10−9 m. The units of mass are specified in terms of the gram, e.g., microgram (μg) = 10−9 kg.

Only one prefix is used with a unit; the use of units such as the millimicrometer is no longer acceptable. When a unit is raised to a power, the power applies to the prefix as well, e.g., a cubic millimeter (mm3) = 10−9 m3. When a prefix is used with a ratio unit, it should be in the numerator rather than in the denominator, e.g., kilometers/second (km/s) rather than meters/millisecond (m/ms). Only prefixes denoting powers of 103 are normally used. Hecto-, deka-, deci-, and centi- are usually attached only to the metric system units gram, meter, and liter.

Owing to the force of tradition, one noncoherent unit, the liter, equal to 10−3 m3, or 1 dm3, is generally accepted for use with SI. The internationally accepted abbreviation for liter is the letter l; however, this can be confused with the numeral 1, especially in typescript. For this reason, the capital letter L is also used as a symbol for liter. The lower case letter is generally used with prefixes, e.g., dl, ml, fl. The symbols for all other SI units begin with a capital letter if the unit is named after a person and with a lower case letter otherwise. The name of a unit is never capitalized.

SI

Abbreviation for International System of Units (Système International d'Unités).

Si

Symbol for silicon.

sI

Abbreviation for 6-mercaptopurine ribonucleoside (or 6-thioinosine).

SI

Système International d'Unités, or International System of Units. See SI unit, under unit.

Si

silicon.

Si

symbol for the element silicon.

SI

abbreviation for Systèeme International d'Unités, the French name for the International System of Units.

SI

Abbreviation for:
International System of Units 
sacroiliac
safety index
sagittal index
saline infusion
satiety index
saturation index
secondary infertility
seed implantation
selectivity index
self-inflicted
self-injury
sensitivity index
serious illness
serious injury
seriously ill
sexual intercourse
sexually inactive
sexually inexperienced
serum iron
severity index
shock index
signal intensity
silent infarction
silent ischaemia
silicone
silver
Singh Index
sinus irregularities
situs inversus
small intestine
smoke inhalation
smoking index
snoring index
social interaction
Special Investigator
speech impaired
spinal injury
stability index
stratum intermedium
statutory instrument 
stress incontinence
stroke index
Structured Interview 
suicidal ideation
superior/inferior
survival index
systolic index

SI

Lab medicine Systeme International d'unites, Intl System of units The international system for standardization of units of measurement; the SI is a refinement and extension of the metric system
1. Sacroiliac.
2. Saline injection
.
3. Saturation index.
4. School inventory–psychological test.
5. Sex inventory–psychological evaluation.

SI

Abbreviation for International System of Units; sensory integration.

Si

Symbol for silicon.

SI,

n small intestine channel; an acupuncture channel running from the hand to the face along the ulnar surface of the arm and associated with the heart (HT) channel. See also HT.
Enlarge picture
SI.

SI(J),

n See sacroiliac joint.
Enlarge picture
SI(J).

SI

Abbreviation for International System of Units.

Si

Symbol for silicon.

Si

chemical symbol, silicon.