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Lentoid
Lentoid is a geometric shape of a three-dimensional body, best described as a circle viewed from one direction and a convex lens viewed from every orthogonal direction. It has no strict mathematical definition, but may be described as the volume enclosed within overlapping paraboloids. The term is most often used in describing jewelry and cellular phenomena in microbiology. In history Since ancient times, the lentoid shape has been used to fashion jewelry and seals for identification made from a variety of gemstones and metals. In Minoan Crete, for example, Minoan seals have been found with complex carving on lentoid stones. The lentoid shape was one of the most commonly recovered seal shapes from Minoan Knossos on Crete dating to the Bronze Age, as evidenced by the finds at that Bronze Age palace.C. Michael Hogan''Knossos fieldnotes'', Modern Antiquarian (2007)/ref> Gallery File:Agate lentoid seal MET DP141655 DP141657.jpg, Lentoid Minoan seal in agate: seal and impre ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minoan Seals
Minoan seals are impression seals in the form of carved gemstones and similar pieces in metal, ivory and other materials produced in the Minoan civilization. They are an important part of Minoan art, and have been found in quantity at specific sites, for example in Knossos, Mallia and Phaistos. They were evidently used as a means of identifying documents and objects. Minoan seals are of a small size, 'pocket-size', in the manner of a personal amulet. Many of the images are a similar size to a human fingernail, with a high proportion that of the nail of a little finger. They might be thought of as equivalent to the pocket-sized, scaraboid seals of Ancient Egypt, which were sometimes imitated in Crete. However Minoan seals can be larger, with largest examples of many inches. Minoan seals are the most common surviving type of Minoan art after pottery, with several thousand known, from EM II onwards, in addition to over a thousand impressions, few of which match surviving seal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic, and are ground and polished or molded to a desired shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called lenses, such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices like telescopes, binoculars and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word '' lens'' comes from '' lēns'', the Latin name of the lentil (a seed of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bronze Age
The Bronze Age is a historic period, lasting approximately from 3300 BC to 1200 BC, characterized by the use of bronze, the presence of writing in some areas, and other early features of urban civilization. The Bronze Age is the second principal period of the three-age system proposed in 1836 by Christian Jürgensen Thomsen for classifying and studying ancient societies and history. An ancient civilization is deemed to be part of the Bronze Age because it either produced bronze by smelting its own copper and alloying it with tin, arsenic, or other metals, or traded other items for bronze from production areas elsewhere. Bronze is harder and more durable than the other metals available at the time, allowing Bronze Age civilizations to gain a technological advantage. While terrestrial iron is naturally abundant, the higher temperature required for smelting, , in addition to the greater difficulty of working with the metal, placed it out of reach of common use until th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lists Of Shapes
Lists of shapes cover different types of geometric shape and related topics. They include mathematics topics and other lists of shapes, such as shapes used by drawing or teaching tools. Mathematics * List of mathematical shapes * List of two-dimensional geometric shapes ** List of triangle topics ** List of circle topics * List of curves * List of surfaces * List of polygons, polyhedra and polytopes ** List of regular polytopes and compounds Elsewhere * Solid geometry, including table of major three-dimensional shapes * Box-drawing character * Cuisenaire rods (learning aid) * Geometric shape * Geometric Shapes (Unicode) * Glossary of shapes with metaphorical names * List of symbols * Pattern Blocks Pattern Blocks are a set of mathematical manipulatives developed in the 1960s. The six shapes are both a play resource and a tool for learning in mathematics, which serve to develop spatial reasoning skills that are fundamental to the learning of ... (learning aid) {{DEFAU ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spheroid
A spheroid, also known as an ellipsoid of revolution or rotational ellipsoid, is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. A spheroid has circular symmetry. If the ellipse is rotated about its major axis, the result is a ''prolate spheroid'', elongated like a rugby ball. The American football is similar but has a pointier end than a spheroid could. If the ellipse is rotated about its minor axis, the result is an ''oblate spheroid'', flattened like a lentil or a plain M&M. If the generating ellipse is a circle, the result is a sphere. Due to the combined effects of gravity and rotation, the figure of the Earth (and of all planets) is not quite a sphere, but instead is slightly flattened in the direction of its axis of rotation. For that reason, in cartography and geodesy the Earth is often approximated by an oblate spheroid, known as the reference ellipsoid, instead of a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Disc (mathematics)
In geometry, a disk (also spelled disc). is the region in a plane bounded by a circle. A disk is said to be ''closed'' if it contains the circle that constitutes its boundary, and ''open'' if it does not. For a radius, r, an open disk is usually denoted as D_r and a closed disk is \overline. However in the field of topology the closed disk is usually denoted as D^2 while the open disk is \operatorname D^2. Formulas In Cartesian coordinates, the ''open disk'' of center (a, b) and radius ''R'' is given by the formula :D=\ while the ''closed disk'' of the same center and radius is given by :\overline=\. The area of a closed or open disk of radius ''R'' is π''R''2 (see area of a disk). Properties The disk has circular symmetry. The open disk and the closed disk are not topologically equivalent (that is, they are not homeomorphic), as they have different topological properties from each other. For instance, every closed disk is compact whereas every open disk is not compact. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agate
Agate () is a common rock formation, consisting of chalcedony and quartz as its primary components, with a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks. The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus Valley civilisation. Etymology The stone was given its name by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shore line of the Dirillo River or Achates ( grc, Ἀχάτης) in Sicily, sometime between the 4th and 3rd centuries BCE. Formation and properties Agate minerals have the tendency to form on or within pre-existing rocks, creating difficulties in accurately determining their time of formation. Their host rocks have been dated to have formed as early as the Archean Eon. Agates are most commonly found as n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minoan Seal
The Minoan civilization was a Bronze Age Aegean civilization on the island of Crete and other Aegean Islands, whose earliest beginnings were from 3500BC, with the complex urban civilization beginning around 2000BC, and then declining from 1450BC until it ended around 1100BC, during the early Greek Dark Ages, part of a wider bronze age collapse around the Mediterranean. It represents the first advanced civilization in Europe, leaving behind a number of massive building complexes, Minoan art, sophisticated art, and writing systems. Its economy benefited from a network of trade around much of the Mediterranean. The civilization was rediscovered at the beginning of the 20th century through the work of British archaeologist Sir Arthur Evans. The name "Minoan" derives from the mythical Minos, King Minos and was coined by Evans, who identified the site at Knossos with the labyrinth of the Minotaur. The Minoan civilization has been described as the earliest of its kind in Europe, and his ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Knossos
Knossos (also Cnossos, both pronounced ; grc, Κνωσός, Knōsós, ; Linear B: ''Ko-no-so'') is the largest Bronze Age archaeological site on Crete and has been called Europe's oldest city. Settled as early as the Neolithic period, the name Knossos survives from ancient Greek references to the major city of Crete. The palace of Knossos eventually became the ceremonial and political centre of the Minoan civilization and culture. The palace was abandoned at some unknown time at the end of the Late Bronze Age, c. 1380–1100 BC; the reason is unknown, but one of the many disasters that befell the palace is generally put forward. In the First Palace Period (around 2000 BC), the urban area reached a size of as many as 18,000 people. Spelling The name Knossos was formerly Latinized as Cnossus or Cnossos and occasionally Knossus, Gnossus, or Gnossos but is now almost always written Knossos. Neolithic period The site of Knossos has had a very long history of human habitation b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paraboloid
In geometry, a paraboloid is a quadric surface that has exactly one axis of symmetry and no center of symmetry. The term "paraboloid" is derived from parabola, which refers to a conic section that has a similar property of symmetry. Every plane section of a paraboloid by a plane parallel to the axis of symmetry is a parabola. The paraboloid is hyperbolic if every other plane section is either a hyperbola, or two crossing lines (in the case of a section by a tangent plane). The paraboloid is elliptic if every other nonempty plane section is either an ellipse, or a single point (in the case of a section by a tangent plane). A paraboloid is either elliptic or hyperbolic. Equivalently, a paraboloid may be defined as a quadric surface that is not a cylinder, and has an implicit equation whose part of degree two may be factored over the complex numbers into two different linear factors. The paraboloid is hyperbolic if the factors are real; elliptic if the factors are complex con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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