Pm


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Pm,

symbol for the element promethiumpromethium
, artificially produced radioactive chemical element; symbol Pm; at. no. 61; mass no. of most stable isotope 145; m.p. 1,042°C;; b.p. 3,000°C; (estimated); sp. gr. unknown; valence +3.
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Pm

(chemistry)

PM

(electromagnetism)
(communications)
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

PM

(1)

PM

(2)

PM

(3)
["PM, A System for Polynomial Manipulations", G.E. Collins, CACM 9(8):578-589 (Aug 1966)].

pm

(networking)
The country code for St. Pierre and Miquelon.
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package manager

Software that installs and updates applications in a Linux or Unix environment. A package manager supports the version of the OS being used and functions as the control program for installations and updates. To install another app, users open their package manager (PM) and search by title. Linux package managers are like online app stores that download, install and update the apps.

In contrast, when an app is downloaded directly from a vendor, as have Windows and Mac apps for decades, the apps self-install, and the vendors notify the users when an update is ready. However, there are so many different versions of Linux that distributors are obliged to compile a wide variety of free apps and utilities to make sure they work and store them in their own repository. See Linux, Unix and install program.

phase modulation

Varying the angle of a wave in a carrier in order to transmit analog or digital data. For digital signals, phase modulation (PM) is widely used in conjunction with amplitude modulation (AM). For example, quadrature amplitude modulation (QAM) uses both phase and amplitude modulation to create different binary states for transmission (see QAM). See modulation and carrier.


Vary the Angle
In PM modulation, the angle of the carrier wave is varied by the incoming signal. In this example, the modulating wave implies an analog signal.







Digital Phase Shift Keying (PSK)
For digital signals, phase shift keying (PSK) uses two phases for 0 and 1 as in this example. See DPSK.

Presentation Manager

A graphical user interface (GUI) library used to develop OS/2 applications. Character-based OS/2 applications can be developed similar to DOS applications, but OS/2 PM applications are graphics based like Mac, Windows and Motif applications. The term used to be the name of the interface itself, which was later named Workplace Shell.

preventive maintenance

Inspecting hardware on a regular basis to ensure it stays in good running order. Preventive maintenance generally implies taking the equipment out of operation during the maintenance period. In the 1960s and 1970s, preventive maintenance took hours every week or every month and was performed by a field engineer.

Starting in the 1980s, computers began to run without breaking down for weeks and months on end, and preventive maintenance became less of an issue over time. Today, electronic devices are rarely taken out of operation on a regular basis. The only exception is the periodic cleaning of automatic feeders and paper paths in high-volume printers and scanners. See remedial maintenance and percussive maintenance.

Program Manager

The control center for Windows 3.x operation, which was introduced in 1990. It provided the means to launch applications and manage the desktop. Although the interface changed in Windows 95, Program Manager remained an option for a while (PROGMAN.EXE was included in Windows 95/98, NT 4.0 and 2000). See File Manager. See Win 3.1/9x differences.


Program Manager
Program Manager used resizable windows to group application icons to suit a user's work style. Many users found program launching easier with Program Manager than with the Start menu, and Program Manager remained available as an option for a while.







What Goes Around Comes Around
Reminiscent of Program Manager, the Mac Launchpad interface was added in 2011 to follow in the footsteps of the iPhone/iPad home screen (see Launchpad).
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