Conical hill

A conical hill (also cone or conical mountain) is a landform with a distinctly conical shape. It is usually isolated or rises above other surrounding foothills, and is often, but not always, of volcanic origin.

Conical hills or mountains occur in different shapes and are not necessarily geometrically-shaped cones; some are more tower-shaped or have an asymmetric curve on one side. Typically, however, they have a circular base and smooth sides with a gradient of up to 30°. Such conical mountains are found in all volcanically-formed areas of the world such as the Bohemian Central Uplands in the Czech Republic, the Rhön in Germany or the Massif Central in France.

Term

Cone cell

Cone cells, or cones, are one of two types of photoreceptor cells in the retina of the eye. They are responsible for color vision and function best in relatively bright light, as opposed to rod cells, which work better in dim light. Cone cells are densely packed in the fovea centralis, a 0.3 mm diameter rod-free area with very thin, densely packed cones which quickly reduce in number towards the periphery of the retina. There are about six to seven million cones in a human eye and are most concentrated towards the macula.

A commonly cited figure of six million in the human eye was found by Osterberg in 1935. Oyster's textbook (1999) cites work by Curcio et al. (1990) indicating an average close to 4.5 million cone cells and 90 million rod cells in the human retina.

Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of colour. They are also able to perceive finer detail and more rapid changes in images, because their response times to stimuli are faster than those of rods. Cones are normally one of the three types, each with different pigment, namely: S-cones, M-cones and L-cones. Each cone is therefore sensitive to visible wavelengths of light that correspond to short-wavelength, medium-wavelength and long-wavelength light. Because humans usually have three kinds of cones with different photopsins, which have different response curves and thus respond to variation in colour in different ways, we have trichromatic vision. Being colour blind can change this, and there have been some verified reports of people with four or more types of cones, giving them tetrachromatic vision. The three pigments responsible for detecting light have been shown to vary in their exact chemical composition due to genetic mutation; different individuals will have cones with different color sensitivity. Destruction of the cone cells from disease would result in blindness.

Cone (linear algebra)

In linear algebra, a (linear) cone is a subset of a vector space that is closed under multiplication by positive scalars. In other words, a subset C of a real vector space V is a cone if and only if λx belongs to C for any x in C and any positive scalar λ of V (or, more succinctly, if and only if λC = C for any positive scalar λ).

A cone is said to be pointed if it includes the null vector (origin) 0; otherwise it is said to be blunt. Some authors use "non-negative" instead of "positive" in this definition of "cone", which restricts the term to the pointed cones only. In other contexts, a cone is pointed if the only linear subspace contained in it is {0}.

The definition makes sense for any vector space V which allows the notion of "positive scalar" (i.e., where the ground field is an ordered field), such as spaces over the rational, real algebraic, or (most commonly) real numbers.

The concept can also be extended for any vector space V whose scalar field is a superset of those fields (such as the complex numbers, quaternions, etc.), to the extent that such a space can be viewed as a real vector space of higher dimension.

Volcanic cone

Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption. Types of volcanic cones include stratocones, spatter cones, tuff cones, and cinder cones.

Stratocone

Stratocones are large cone-shaped volcanoes made up of lava flows, explosively erupted pyroclastic rocks, and igneous intrusives that are typically centered around a cylindrical vent. Unlike shield volcanoes, they are characterized by a steep profile and periodic, often alternating, explosive eruptions and effusive eruptions. Some have collapsed craters called calderas. The central core of a stratocone is commonly dominated by a central core of intrusive rocks that range from around 500 meters (1,600 ft) to over several kilometers in diameter. This central core is surrounded by multiple generations of lava flows, many of which are brecciated, and a wide range of pyroclastic rocks and reworked volcanic debris. The typical stratocone is an andesitic to dacitic volcano that is associated with subduction zones. They are also known as either stratified volcano, composite cone, bedded volcano, cone of mixed type or Vesuvian-type volcano.

Hill

A hill is a landform that extends above the surrounding terrain. It often has a distinct summit, although in areas with scarp/dip topography a hill may refer to a particular section of flat terrain without a massive summit (e.g. Box Hill, Surrey).

Terminology

The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be less tall and less steep than a mountain. In the United Kingdom, geographers historically regarded mountains as hills greater than 1,000 feet (300 m) above sea level, which formed the basis of the plot of the 1995 film The Englishman Who Went Up a Hill But Came Down a Mountain. In contrast, hillwalkers have tended to regard mountains as peaks 2,000 feet (610 m) above sea level: the Oxford English Dictionary also suggests a limit of 2,000 feet (610 m) and Whittow states "Some authorities regard eminences above 600 m (2,000 ft) as mountains, those below being referred to as hills." The Great Soviet Encyclopedia defines hill as an upland with a relative height up to 200 m (660 ft).

Hill (crater)

Hill is a small lunar impact crater that is located to the west of the prominent crater Macrobius, near the eastern edge of the Sinus Amoris. This crater was previously designated Macrobius B before being given a name by the IAU. It lies just to the north-northeast of Carmichael, another renamed satellite crater of Macrobius.

This is a circular, bowl-shaped crater with an inner wall that has a relatively high albedo compared to the surrounding terrain. The inner walls are symmetrical in form, and slope gently down to the small floor at the midpoint, a surface about one-fourth the diameter of the crater. This formation is not significantly eroded, and is otherwise indistinguishable from many similar craters on the Moon.

References

Hill (disambiguation)

Hill usually refers to a raised landform.

Hill may also refer to:

In places:

Canada

England

United States

See also