| 释义 |
gradient, a. and n.|ˈgreɪdɪənt|
[ad. L. gradient-em pr. pple. of gradī to walk, f. grad-us step.]
A. adj.
1. a. Of animals: Characterized by taking steps with the feet, as their distinctive mode of progression; walking, ambulant.
1641Wilkins Math. Magick ii. iv. (1648) 174 Amongst these gradient Automata, that iron spider mentioned in Walchius is more especially remarkable. 1663R. Boyle Usef. Exp. Nat. Philos. i. ii. 40 But it is not so conspicuous in gradient animals (if I may so speak) as in swimming ones. 1668Wilkins Real Char. 161 Oviparous Beasts..Gradient; having four feet. 1822T. Taylor Apuleius 300 There are animals adapted to the several parts, the volant living in the air, and the gradient on the earth.
b. Her. Said of a tortoise depicted as walking.
1780Edmondson Her. II. Gloss. 1828–40Berry Encycl. Her. I.
2. Of a railway line: Rising or descending by regular degrees of inclination. rare—0. (? A figment.)
1855in Ogilvie, Suppl. Hence in mod. Dicts.
B. n.
1. a. Of a road or railway: Amount of inclination to the horizontal; degree of slope; = grade n. 10.
This sense can hardly have been evolved from that of the Lat. pple. or the Eng. adj.; possibly it was a new formation on grade, after the supposed analogy of quotient.
1835Railway Mag. Dec. 264 The line of Railroad here proposed..passing over the most easy and beautiful tract of country..with the most favourable gradients. 1836Dubl. Rev. May 225 In describing the gradients of a railway, it is usual to state the rise per mile in feet. 1836Mech. Mag. 6 Aug. XXV. 317 In a contemporary journal there appears a violent tirade against the word gradient as at present used by civil engineers. 1861Smiles Engineers II. 429 One in thirty being about the severest gradient at any part of the road. 1868Peard Water-Farm. xi. 111 Wherever they have been constructed on a gradient of 1 in 9..they have answered admirably. 1880Haughton Phys. Geog. v. 241 The uniformly increasing gradient with which the pampas everywhere rise. 1884American VIII. 86 The road was built with needlessly steep gradients.
fig.1868W. H. Dixon Spirit Wives I. xv. 159 That duality in the soul of nature..led by an easy gradient into a state of manners, as between brother and sister, which [etc.].
b. A part of a road which slopes upward or downward; a portion of a way not level.
1845Rep. Brit. Assoc. 1844 ii. 96 It was necessary that that railway should present long and very steep gradients. 1915R. B. Holt Tramway Track Constr. & Maintenance ix. 114 The wear on the rails on all parts of the gradient, both on the up track and on the down track, is exceedingly irregular. 1971Homes & Gardens Aug. 90/1 The train..could be heard puffing like an old man, ‘Chuff, chuff, chuff’, as it travelled up the gradient approaching the cutting. 1971Daily Tel. (Colour Suppl.) 27 Aug. 12/3 Snow drove into our faces and on the steep gradients where skis had to be removed we stumbled in deep powder.
2. transf. Orig., the proportional amount of rise or fall of the barometer or thermometer in passing from one region to another. Now in wider use: a continuous increase or decrease in the magnitude of any quantity or property along a line from one point to another; also, the rate of this change, expressed as the change in magnitude per unit change in distance.
The ‘barometric gradient’ is expressed in hundredths of an inch to a degree of a great circle; thus ‘a gradient of 4 means that over a distance of 60 nautical miles, the barometer rises 4/100 or 1/25 of an inch’ (Huxley Physiogr. 95).
1870Everett Deschanel's Nat. Philos. xiii. 168 Generally speaking, the wind blows from regions of high to regions of low barometer, and with greater force as the barometric gradient is steeper. 1876Tait Rec. Adv. Phys. Sci. xi. 263 The temperature will fall off by a uniform gradient. 1878Huxley Physiogr. 95 If the isobars run close together it shows that the gradient is high, and therefore the winds will be strong. 1880Times 11 Aug. 11/6 Gradients for westerly winds lay over Scotland, and for easterly winds over the Bay of Biscay. 1882Nature XXVI. 11 The primary cause of cyclones, according to Ferrel, is a horizontal temperature gradient. 1886J. A. Fleming Short Lect. Electr. Artisans vii. 122 Along the lead there is a regular fall or gradient of [electrical] pressure. 1892W. Peddie Man. Physics ix. 132 The rate of variation of density per unit of length is r... The quantity r is generally called the ‘concentration-gradient’. 1898Proc. R. Soc. LXIII. 364 The kathode fall is constant for all pressures and currents whilst the potential gradient along the rest of the tube is variable. 1902Poynting & Thomson Prop. Matter xviii. 205 The ratio of the stress to the velocity gradient is called the viscosity of the fluid. 1910Encycl. Brit. V. 891/2 This outflow of heat necessitates a rise of temperature with increase of depth. The corresponding gradient is of the order of 1°C. in 100 ft. 1948Glasstone Textbk. Physical Chem. (ed. 2) iv. 260 The gradient is actually negative, that is the concentration decreases from left to right. 1957Encycl. Brit. X. 681/2 He proposed to measure the rate of change or gradients in the gravitational field. 1962A. R. W. Hayes Revision Physics 98 We must measure..the uniform temperature gradient along the bar—found from readings of thermometers placed in mercury..in holes bored in the specimen. 1970Nature 19 Dec. 1225/1 There is a gradient of dormancy within the spikelet, the larger proximal seed being less dormant than the smaller distal seed, while a much smaller third seed..is extremely dormant.
b. spec. in Embryol., such an increase or decrease, along an axis of an organism or a part, in the potential for developing into an organ or in a related bodily process.
1911[see axial gradient]. 1915C. M. Child Individuality in Organisms iii. 65 Gradients in rate of cell division, size of cells, condition or amount of protoplasm in the cells, rate of growth, and rate and sequence of differentiation are very characteristic features of both animal and plant development. Such gradients are definitely related to the axes of the individual or its parts, and are..expressions of axial metabolic gradients. 1924Bellamy & Child in Proc. R. Soc. B. XCVI. 141 In a protoplasm of specific hereditary constitution, such a gradient is adequate as the initiating factor in the axial differentiation characteristic of that species. 1927[see field n. 17 c]. 1953J. S. Huxley Evol. in Action i. 29 Gradients exist in the developing organism—gradients in metabolism, growth-potential, and other factors. Genes altering the shape and intensity of such gradients will affect a number of parts simultaneously. 1957[see field n. 17 c]. 1970F. Crick in Nature 31 Jan. 420/1 It is an old idea that ‘gradients’ are involved in embryological development... Many of the gradients to which Child referred seem more likely, in retrospect, to be the results of development rather than its cause. An outsider to embryology has the impression that in recent years gradients have become a dirty word. Ibid. 422/1 If this approach serves to make the idea of diffusion gradients respectable to embryologists it will have served its purpose.
3. Math. A rational integral function of a number of quantics of assigned weights, which is of one degree and one weight throughout (Prof. Elliott).
1887Sylvester in Amer. Jrnl. Math. IX. 2 A rational intergral homogeneous and isobaric function (or, to avoid a tedious periphrasis, say a gradient). 1895Elliott Algebra Quantics 145, 146, 233.
4. The degree of steepness of a graph at any point, measured by the tangent of the angle between the horizontal axis and either the line (if straight) or the tangent to the curve; (see also quot. 1937).
1897H. Lamb Elem. Course Infinitesimal Calculus ii. 67 It is convenient to have a name for the property of a curve which is measured by the derived function. We shall use the term ‘gradient’ in this sense. 1937E. J. McShane tr. Courant's Diff. & Integral Calculus (ed. 2) I. xi. 90 The slope or gradient of the curve is given by tan a, and hence the term gradient is occasionally used for the derivative of the function represented by the curve. 1942C. E. K. Mees Theory Photogr. Process xix. 702 The D, log E curve continues..into the region of decreasing exposure with constantly decreasing gradient. 1958A. Barton Introd. Coordinate Geom. v. 64 A line whose gradient is zero is parallel to the x-axis; as the gradient increases the line gets steeper. Ibid. 66 Two lines are..perpendicular if the product of their gradients is -1.
5. Math. A vector function whose components along the co-ordinate axes are the partial derivatives with respect to the corresponding variables of a given scalar function; it is denoted by ∇f (see del) or by grad f, where f is the scalar function.
1901E. B. Wilson Vector Analysis iii. 138 The vector sum which is the resultant rate of increase of V is denoted by ∇V... The terms gradient and slope of V are..used for ∇V. 1936E. J. McShane tr. Courant's Diff. & Integral Calculus II. iii. 89 The direction of the gradient is the direction in which the function increases most rapidly. 1966McGraw-Hill Encycl. Sci. & Technol. II. 413/1 There are three differentiation processes that are of conceptual value in the study of vectors: the gradient of a scalar, the divergence of a vector, and the curl of a vector.
6. attrib. and Comb., as gradient wind Meteorol., the (hypothetical) wind whose direction is that of the geostrophic wind but whose speed is calculated by allowing for the effect on the geostrophic wind of the centrifugal force that results from its curved path.
1908E. Gold Barometric Gradient & Wind Force 24 We can construct a scale..which shall give..the Beaufort number corresponding to the theoretical gradient wind for straight isobars for any pressure distribution. 1928[see geostrophic a.]. 1966McGraw-Hill Encycl. Sci. & Technol. VI. 244/2 The gradient wind is a good approximation to the actual wind and is often superior to the geostrophic wind, particularly when the flow is strongly curved in the cyclonic sense. |