| 1. | Past Master. |
| 2. | Paymaster. |
| 3. | p.m. |
| 4. | Police Magistrate. |
| 5. | Postmaster. |
| 6. | post-mortem. |
| 7. | Prime Minister. |
| 8. | Provost Marshal. |
| 1. | after noon. |
| 2. | the period between noon and midnight. |
| particulate matter n. Abbr. PM Material suspended in the air in the form of minute solid particles or liquid droplets, especially when considered as an atmospheric pollutant. |
| phase modulation n. Abbr. pm or p-m A type of electronic modulation in which the phase of a carrier wave is varied in order to transmit the information contained in the signal. |
| pm or p-m abbr. phase modulation |
| Pm The symbol for the element promethium. |
| PM abbr.
|
| prime minister n. Abbr. PM
|
pro·me·thi·um  (prə-mē'thē-əm)  n. Symbol Pm A radioactive rare-earth element prepared by fission of uranium or by neutron bombardment of neodymium, having 14 isotopes with mass numbers ranging from 141 to 154 and used as a source of beta rays. Atomic number 61; melting point 1,168°C; boiling point 2,460°C; valence 3. See Table at element. [From Prometheus.] |
pm abbr.
picometer
Pm
The symbol for the element promethium.
| Pm
The symbol for promethium. |
| promethium (prə-mē'thē-əm) Pronunciation Key
Symbol Pm A radioactive metallic element of the lanthanide series. Promethium does not occur in nature but is prepared through the fission of uranium. It has 17 isotopes, one of which is used to make long-lived miniature batteries that work at extreme temperatures for up to five years. The longest-lived isotope, Pm 147, has a half-life of 2.5 years and is used as a source of beta rays. Atomic number 61; melting point 1,168°C; boiling point 2,460°C; valence 3. See Periodic Table. |
PM
1. preventive maintenance.
2. Presentation Manager
3. ["PM, A System for Polynomial Manipulations", G.E. Collins, CACM 9(8):578-589 (Aug 1966)].
[The Jargon File]
pm networking
The country code for St. Pierre and Miquelon.
(1999-01-27)
pm
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| pM picomolar |
| Pm promethium |
PM
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Pm
(Pm), chemical element, only rare-earth metal of transition Group IIIb of the periodic table not detected in nature. Conclusive chemical proof of the existence of promethium, the last of the rare-earth elements to be discovered, was obtained (1947) by J.A. Marinsky, L.E. Glendenin, and C.D. Coryell, who isolated the radioactive isotope promethium-147 (2.7-year half-life) from uranium fission products at the research site at Oak Ridge, Tenn. Identification was firmly established by spectroscopy. Earlier investigators thought that they had found the element with atomic number 61 in naturally occurring rare earths and had prematurely called it illinium and florentium. Promethium-147 is effectively separated from the other rare-earth fission products by an ion-exchange method. Its soft beta radiation is converted to electricity in miniature batteries formed by sandwiching promethium between wafers of a semiconductor such as silicon; these batteries operate in extreme temperatures for five years. Promethium has also been prepared by slow neutron bombardment of the isotope neodymium-146; the resultant isotope, neodymium-147, decays by electron emission to promethium-147. The metal itself was first prepared (1963) by reduction of the fluoride, PmF3, with lithium
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