adj.

らせんの、らせん状の、ヘリカルな、ヘリックスの

関: helices、helix、spiral

WordNet

form a spiral; "The path spirals up the mountain"
a continuously accelerating change in the economy
a plane curve traced by a point circling about the center but at increasing distances from the center
ornament consisting of a curve on a plane that winds around a center with an increasing distance from the center (同)volute
flying downward in a helical path with a large radius
a curve that lies on the surface of a cylinder or cone and cuts the element at a constant angle (同)spiral

PrepTutorEJDIC

らせん形の
らせん(helix) / らせん状のもの;らせんばね;巻き貝 / (物価・賃金などの)らせん状上昇(下降) / らせん状の /… ‘を'らせん形にする / らせん形になる;らせん状に動く
らせん / らせん形のもの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/07/27 21:27:04」(JST)

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[Wiki en表示]

This article is about the shape. For other uses, see Helix (disambiguation).

The helix (cos t, sin t, t) from t = 0 to 4π with arrowheads showing direction of increasing t

A helix (pl: helixes or helices) is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for example, a spiral ramp – is called a helicoid.^[1] Helices are important in biology, as the DNA molecule is formed as two intertwined helices, and many proteins have helical substructures, known as alpha helices. The word helix comes from the Greek word ἕλιξ, "twisted, curved".^[2]

Types[edit]

Helices can be either right-handed or left-handed. With the line of sight along the helix's axis, if a clockwise screwing motion moves the helix away from the observer, then it is called a right-handed helix; if towards the observer, then it is a left-handed helix. Thus, a helix cannot be described as 'spinning clockwise or counter-clockwise.' Handedness (or chirality) is a property of the helix, not of the perspective: a right-handed helix cannot be turned or flipped to look like a left-handed one unless it is viewed in a mirror, and vice versa.

Most hardware screw threads are right-handed helices. The alpha helix in biology as well as the A and B forms of DNA are also right-handed helices. The Z form of DNA is left-handed.

The pitch of a helix is the width of one complete helix turn, measured parallel to the axis of the helix.

A double helix consists of two (typically congruent) helices with the same axis, differing by a translation along the axis.^[3]

A conic helix may be defined as a spiral on a conic surface, with the distance to the apex an exponential function of the angle indicating direction from the axis. An example is the Corkscrew roller coaster at Cedar Point amusement park.

A circular helix, (i.e. one with constant radius) has constant band curvature and constant torsion.

A curve is called a general helix or cylindrical helix^[4] if its tangent makes a constant angle with a fixed line in space. A curve is a general helix if and only if the ratio of curvature to torsion is constant.^[5]

A curve is called a slant helix if its principal normal makes a constant angle with a fixed line in space.^[6] It can be constructed by applying a transformation to the moving frame of a general helix.^[7]

Mathematical description[edit]

A helix composed of sinusoidal x and y components

In mathematics, a helix is a curve in 3-dimensional space. The following parametrisation in Cartesian coordinates defines a helix:^[8]

As the parameter t increases, the point (x(t),y(t),z(t)) traces a right-handed helix of pitch 2π and radius 1 about the z-axis, in a right-handed coordinate system.

In cylindrical coordinates (r, θ, h), the same helix is parametrised by:

A circular helix of radius a and pitch 2πb is described by the following parametrisation:

Another way of mathematically constructing a helix is to plot a complex valued exponential function (e^xi) taking imaginary arguments (see Euler's formula).^[vague]

Except for rotations, translations, and changes of scale, all right-handed helices are equivalent to the helix defined above. The equivalent left-handed helix can be constructed in a number of ways, the simplest being to negate any one of the x, y or z components.

Arc length, curvature and torsion[edit]

The length of a circular helix of radius a and pitch 2πb expressed in rectangular coordinates as

equals , its curvature is and its torsion is

Examples[edit]

In music, pitch space is often modeled with helices or double helices, most often extending out of a circle such as the circle of fifths, so as to represent octave equivalency.

Crystal structure of a folded molecular helix reported by Lehn et al. in Helv. Chim. Acta., 2003, 86, 1598–1624.
A natural left-handed helix, made by a climber plant.
A charged particle in a uniform magnetic field following a helical path.
A helical coil spring.

References[edit]

^ Weisstein, Eric W., "Helicoid", MathWorld.
^ ἕλιξ, Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus
^ "Double Helix" by Sándor Kabai, Wolfram Demonstrations Project.
^ O'Neill, B. Elementary Differential Geometry, 1961 pg 72
^ O'Neill, B. Elementary Differential Geometry, 1961 pg 74
^ Izumiya, S. and Takeuchi, N. (2004) New special curves and developable surfaces. Turk J Math, 28:153–163.
^ Menninger, T. (2013), An Explicit Parametrization of the Frenet Apparatus of the Slant Helix. arXiv:1302.3175.
^ Weisstein, Eric W., "Helix", MathWorld.

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