英文字典中文字典


英文字典中文字典51ZiDian.com



中文字典辞典   英文字典 a   b   c   d   e   f   g   h   i   j   k   l   m   n   o   p   q   r   s   t   u   v   w   x   y   z       







请输入英文单字,中文词皆可:

foci    
focus的复数形

focus的复数形

Focus \Fo"cus\ (f[=o]"k[u^]s), n.; pl. E. {Focuses}
(f[=o]"k[u^]s*[e^]z), L. {Foci} (f[=o]"s[imac]). [L. focus
hearth, fireplace; perh. akin to E. bake. Cf. {Curfew},
{Fuel}, {Fusil} the firearm.]
1. (Opt.) A point in which the rays of light meet, after
being reflected or refracted, and at which the image is
formed; as, the focus of a lens or mirror.
[1913 Webster]

2. (Geom.) A point so related to a conic section and certain
straight line called the directrix that the ratio of the
distance between any point of the curve and the focus to
the distance of the same point from the directrix is
constant.
[1913 Webster]

Note: Thus, in the ellipse FGHKLM, A is the focus and CD the
directrix, when the ratios FA:FE, GA:GD, MA:MC, etc.,
are all equal. So in the hyperbola, A is the focus and
CD the directrix when the ratio HA:HK is constant for
all points of the curve; and in the parabola, A is the
focus and CD the directrix when the ratio BA:BC is
constant. In the ellipse this ratio is less than unity,
in the parabola equal to unity, and in the hyperbola
greater than unity. The ellipse and hyperbola have each
two foci, and two corresponding directrixes, and the
parabola has one focus and one directrix. In the
ellipse the sum of the two lines from any point of the
curve to the two foci is constant; that is: AG GB =
AH HB; and in the hyperbola the difference of the
corresponding lines is constant. The diameter which
passes through the foci of the ellipse is the major
axis. The diameter which being produced passes through
the foci of the hyperbola is the transverse axis. The
middle point of the major or the transverse axis is the
center of the curve. Certain other curves, as the
lemniscate and the Cartesian ovals, have points called
foci, possessing properties similar to those of the
foci of conic sections. In an ellipse, rays of light
coming from one focus, and reflected from the curve,
proceed in lines directed toward the other; in an
hyperbola, in lines directed from the other; in a
parabola, rays from the focus, after reflection at the
curve, proceed in lines parallel to the axis. Thus rays
from A in the ellipse are reflected to B; rays from A
in the hyperbola are reflected toward L and M away from
B.
[1913 Webster]

3. A central point; a point of concentration.
[1913 Webster]

{Aplanatic focus}. (Opt.) See under {Aplanatic}.

{Conjugate focus} (Opt.), the focus for rays which have a
sensible divergence, as from a near object; -- so called
because the positions of the object and its image are
interchangeable.

{Focus tube} (Phys.), a vacuum tube for R[oe]ntgen rays in
which the cathode rays are focused upon the anticathode,
for intensifying the effect.

{Principal focus}, or {Solar focus} (Opt.), the focus for
parallel rays.
[1913 Webster]


请选择你想看的字典辞典:
单词字典翻译
foci查看 foci 在百度字典中的解释百度英翻中〔查看〕
foci查看 foci 在Google字典中的解释Google英翻中〔查看〕
foci查看 foci 在Yahoo字典中的解释Yahoo英翻中〔查看〕





安装中文字典英文字典查询工具!


中文字典英文字典工具:
选择颜色:
输入中英文单字

































































英文字典中文字典相关资料:


  • FOCI Definition Meaning - Merriam-Webster
    The meaning of FOCUS is a center of activity, attraction, or attention How to use focus in a sentence Did you know?
  • Foreign Ownership, Control or Influence
    A company's FOCI factors are reviewed as part of the facility clearance process and throughout the life of the facility security clearance The company's FOCI factors should be documented on the Certificate Pertaining to Foreign Interests (Standard Form 328)
  • What Does the Medical Term “foci” Mean? - Reference. com
    Foci are cells located in a specific organ of the body that are notably different from the surrounding cells These differences are caused by mutation or other types of cellular damage, and they’re generally the first sign of a developing lesion, tumor or other disease
  • What are Foci in the Brain? – Radiology In Plain English
    Medical imaging of the brain sometimes reveals interesting spots or areas in the pictures We call these spots “brain foci ” These brain foci are important because they help doctors understand and take care of problems in your brain
  • FOCI Definition Meaning | Dictionary. com
    Ellipses have two centers, or foci; the more elongated the ellipse, the farther apart these foci are
  • FOCI | English meaning - Cambridge Dictionary
    Language choice and language quality became foci of discussion in newspapers, on television and radio, and on the street
  • Foci - definition of foci by The Free Dictionary
    1 a central point, as of attention or activity 2 a point at which rays of light, heat, or other radiation meet after being refracted or reflected 3 a the focal point of a lens b the focal length of a lens c the clear and sharply defined condition of an image
  • FOCI definition and meaning | Collins English Dictionary
    Rapid, localised infection was populated by discrete foci of persisting virus-infected cells
  • What Does Foci Mean On MRI? | Clarity in Imaging
    In medical imaging, “foci” (singular: “focus”) refers to small, localized areas within the body that may exhibit abnormal characteristics These areas can appear as spots or lesions on an MRI scan and may indicate the presence of various medical conditions
  • Foci Definition Meaning - YourDictionary
    The orbit of the moon around the earth, though not a fixed curve of any class, is elliptical in form, and may be represented by an ellipse which is constantly changing its form and position, and has the earth in one of its foci





中文字典-英文字典  2005-2009