| 释义 |
phi|faɪ|
[The name of ϕ, ϕ, the 21st letter of the Greek alphabet (in Gr. called ϕεῖ).]
1. Petrol. The negative of the logarithm to base 2 of the diameter in millimetres of a particle. Freq. attrib., as phi scale, and written as ϕ.
1934W. C. Krumbein in Jrnl. Sedimentary Petrol. IV. 76, ξ is the numerical value of the diameter... The substitution ϕ = —log2 ξ, or ξ = (½)ϕ, is made in part for typographical convenience, but also to introduce a convenient symbol that may be used for expressing grain diameters. 1936― in Ibid. VI. 38/1 One immediately apparent advantage accruing from the ϕ-scale is the elimination of unwieldy fractions or decimals, such as 1/1024 mm. (0·00098 mm.). Ibid. 45/1 The use of ϕ as the new independent variable..makes available a series of statistical measures based on the moments of the distributions. 1949Ibid. XIX. 76/1 The sieve interval of one phi unit is too large to make the true and nominal mean diameters reasonably equal for all size fractions. 1961Ibid. XXXI. 205/2 Comparison of the mean diameters of each pair of beach-dune samples..shows that there is little difference between the two. In these comparisons, 48 are within 0·2 phi of each other. 1971E. F. McBride in R. E. Carver Procedures Sedimentary Petrol. vi. 110 The Phi scale is now used almost exclusively for computation and is gradually replacing the millimeter scale. 1978Nature 14 Sept. 100/2 The sediments..have mean sizes of 1·6–0·125 mm (—0·7 to 3·0 phi: very coarse to fine sand)... These sands exhibit good sorting, with standard deviations that are generally less than 0·8 phi units.
2. phi coefficient (Statistics): A synonym for the product-moment coefficient of correlation (see product n.1) used when each of the observed variables has only two possible values.
[1904K. Pearson in Drapers' Co. Res. Mem.: Biometric Ser. I. 6, I shall call ϕ2 = χ/ν the mean square contingency. 1913Biometrika IX. 214 We do not agree with him, but it is singular that if he thinks so, he should not have rejected the use of ϕ, the ‘theoretical value of the correlation’.] 1950S. A. Stouffer Measurement & Prediction x. 410 [This] is the Pearson r or the so-called phi-coefficient of the latent fourfold table, which appears here as a mere algebraic byproduct. 1968Blumler & McQuail Television in Politics iv. 75 All the phi coefficients of ·30 or higher (a level which is most unlikely to be reached by chance) were picked out. 1975Morehouse & Stull Statistical Princ. Physical Educ. xi. 235 The phi coefficient is also related to chi-square{ddd}ϕ = √(χ2/N), where N = number of observations. Ibid. 237 The phi coefficient is often recommended for use in the analysis of test items in which the items are scored as correct or incorrect, pass or fail.
3. Nuclear Physics. In full phi meson. A neutral meson that has the same quantum numbers as the omega meson (omega 3 b), is observed as a resonance, has a mass of 1019 MeV (1995 times that of the electron), and on decaying usu. produces two kaons or three pions. Freq. written ϕ.
1962J. J. Sakurai in Physical Rev. Lett. IX. 472/1 In a recent issue of this journal a Brookhaven-Syracuse group reports the possible presence of a narrow resonance (Γ ≈ 20 MeV) in the KK system with mass ≈1020 MeV in the reactions K- + p → K+ + K- + λ, K0 + K0 + λ . In discussing the quantum numbers of the resonating KK pair, which we tentatively refer to as the ϕ meson, [etc.]. Ibid. 474/1 We would like to suggest that this discrepancy is due to mixing between ω and ϕ arising from the fact that the ω and ϕ have the same quantum numbers as far as spin-parity, isospin, and G-parity are concerned. 1968J. Bernstein Elem. Particles vi. 86 Since these objects, the ρ, ω0, ϕ0, are very short-lived (τ∼10-23 sec), it is not really correct, in a rigorous sense, to treat them as if they were stable particles. 1971Sci. Amer. July 100/2 Three vector mesons with zero strangeness are currently known: the rho, the omega and the phi. 1974Nature 6 Dec. 438/2 Another well established meson, called the phi, also has electromagnetic decays to e+e-. 1975Sci. Amer. Oct. 48/2 Zweig's rule was formulated to explain the decay of the phi meson, which is made up of a strange quark and a strange antiquark and has a mass of about 1 GeV. The two particles are closely analogous, but the decay of the J is appreciably slower than that of the phi. |