| 单词 | physics |
| 释义 | physics The science of matter and energy, and their properties and interactions in fields including mechanics, acoustics, optics, heat, electricity, magnetism, radiation, and atomic and nuclear science. Physics is the science of how things work. pi () The sixteenth letter of the Greek alphabet, is used to mathematically represent the ratio of the circumference of a circle to its diameter, which is equal to 3.14159265358979323846. . . . Pi is an infinite decimal, at least as far as we know. Pi has been calculated to many millions of decimal places, but to no end. Further, no repeating pattern has ever been discovered, and many mathematicians maintain that a repeating pattern is impossible. Pi has many important mathematical uses. For example, the area of a circle is pi times the square of the length of the radius, or A = r2 , or pi r squared. Everyone, from middle school, knows that to be impossible, of course — pies are round, some cakes are squared. /4 Differential Quaternary Phase Shift Keying (/4 DQPSK) See /4 DQPSK. /4 DQPSK (/4 Differential Quaternary Phase Shift Keying) A variation on the QPSK modulation technique. /4 DQPSK can be viewed as the superposition of two QPSK constellations offset by 45 degrees relative to each other. /4 DQPSK is specified in cordless telephony standards, including Personal Wireless Telecommunications (PWT and PWT/E), Personal Handyphone Service (PHS), and Personal Communications Service (PCS). /4 DQPSK also is specified in cellular radio standards, including Digital Advanced Mobile Phone Service (D-AMPS) and Personal Digital Cellular (PDC). See also cellular radio, cordless telephone, D-AMPS, modulation, PCS, PDC, PHS, PWT, PWT/E, and QPSK. |
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