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Brass Lectern In The Form Of An Eagle Attributed To Aert Van Tricht The Elder, Limburg (Netherlands)
Brass is an alloy of copper (Cu) and zinc (Zn), in proportions which can be varied to achieve different mechanical, electrical, and chemical properties. It is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure. Brass is similar to bronze, another copper alloy, that uses tin instead of zinc. Both bronze and brass may include small proportions of a range of other elements including arsenic (As), lead (Pb), phosphorus (P), aluminium (Al), manganese (Mn), and silicon (Si). Historically, the distinction between the two alloys has been less consistent and clear, and modern practice in museums and archaeology increasingly avoids both terms for historical objects in favor of the more general "copper alloy". Brass has long been a popular material for decoration due to its bright, gold-like appearance; being used for drawer pulls and doorknobs. It has also been widely used to make utensils because of its low melting ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Persian Astrolabe
Persian may refer to: * People and things from Iran, historically called ''Persia'' in the English language ** Persians, the majority ethnic group in Iran, not to be conflated with the Iranic peoples ** Persian language, an Iranian language of the Indo-European family, native language of ethnic Persians *** Persian alphabet, a writing system based on the Perso-Arabic script * People and things from the historical Persian Empire Other uses * Persian (patience), a card game * Persian (roll), a pastry native to Thunder Bay, Ontario * Persian (wine) * Persian, Indonesia, on the island of Java * Persian cat, a long-haired breed of cat characterized by its round face and shortened muzzle * The Persian, a character from Gaston Leroux's ''The Phantom of the Opera'' * Persian, a List of generation I Pokémon#Persian, generation I Pokémon species * Alpha Indi, star also known as "The Persian" See also * Persian Empire (other) * Persian expedition (other) or Persian ca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Benin Bronzes
The Benin Bronzes are a group of several thousand metal plaques and sculptures that decorated the royal palace of the Kingdom of Benin, in what is now Edo State, Nigeria. Collectively, the objects form the best examples of Benin art and were created from the thirteenth century by artists of the Edo people. Apart from the plaques, other sculptures in brass or bronze include portrait heads, jewelry, and smaller pieces. Many of the dramatic sculptures date to the thirteenth century, and a large part of the collection dates to the fifteenth and sixteenth centuries. It is believed that two "golden ages" in Benin metal workmanship occurred during the reigns of Esigie ( 1550) and of Eresoyen (1735–1750), when their workmanship achieved its highest quality. Most of the plaques and other objects were looted by British forces during the Benin Expedition of 1897 as imperial control was being consolidated in Southern Nigeria. About two hundred pieces were taken to the British Museum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zipper
A zipper, zip, fly, or zip fastener, formerly known as a clasp locker, is a commonly used device for binding together two edges of fabric or other flexible material. Used in clothing (e.g. jackets and jeans), luggage and other bags, camping gear (e.g. tents and sleeping bags), and many other items, zippers come in a wide range of sizes, shapes, and colors. Whitcomb L. Judson, an American inventor from Chicago, in 1892 patented the original design from which the modern device evolved. Description A zipper consists of a slider mounted on two rows of metal or plastic teeth that are designed to interlock and thereby join the material to which the rows are attached. The slider, usually operated by hand, contains a Y-shaped channel that, by moving along the rows of teeth, meshes or separates them, depending on the direction of the slider's movement. The teeth may be individually discrete or shaped from a continuous coil, and are also referred to as ''elements''. The word ''zipp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammunition
Ammunition (informally ammo) is the material fired, scattered, dropped, or detonated from any weapon or weapon system. Ammunition is both expendable weapons (e.g., bombs, missiles, grenades, land mines) and the component parts of other weapons that create the effect on a target (e.g., bullets and warheads). The purpose of ammunition is to project a force against a selected target to have an effect (usually, but not always, lethal). An example of ammunition is the firearm cartridge, which includes all components required to deliver the weapon effect in a single package. Until the 20th century, black powder was the most common propellant used but has now been replaced in nearly all cases by modern compounds. Ammunition comes in a great range of sizes and types and is often designed to work only in specific weapons systems. However, there are internationally recognized standards for certain ammunition types (e.g., 5.56×45mm NATO) that enable their use across different wea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bearing (mechanical)
A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may ''prevent'' a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. Rotary bearings hold rotating components such as shafts or axles within mechanical systems, and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the '' plain bearing'', consists of a shaft rotating in a hole. Lubrication is used to reduce friction. In the ''ball bearing'' and ''roller bearing'', to reduce slid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gear
A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic principle behind the operation of gears is analogous to the basic principle of levers. A gear may also be known informally as a cog. Geared devices can change the speed, torque, and direction of a power source. Gears of different sizes produce a change in torque, creating a mechanical advantage, through their ''gear ratio'', and thus may be considered a simple machine. The rotational speeds, and the torques, of two meshing gears differ in proportion to their diameters. The teeth on the two meshing gears all have the same shape. Two or more meshing gears, working in a sequence, are called a gear train or a '' transmission''. The gears in a transmission are analogous to the wheels in a crossed, belt pulley system. An advantage of gears is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hinge
A hinge is a mechanical bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation: all other translations or rotations being prevented, and thus a hinge has one degree of freedom. Hinges may be made of flexible material or of moving components. In biology, many joints function as hinges, like the elbow joint. History Ancient remains of stone, marble, wood, and bronze hinges have been found. Some date back to at least Ancient Egypt. In Ancient Rome, hinges were called cardō and gave name to the goddess Cardea and the main street Cardo. This name cardō lives on figuratively today as "the chief thing (on which something turns or depends)" in words such as ''cardinal''. According to the OED, the English word hinge is related to '' hang''. Door hinges ; Barrel hinge: A barrel hinge consists of a sectional barrel (the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Padlock
Padlocks are portable locks with a shackle that may be passed through an opening (such as a chain link, or hasp staple) to prevent use, theft, vandalism or harm. Naming and etymology The term '' padlock'' is from the late fifteenth century. The prefix pad- is of unknown origin; it is combined with the noun lock, from Old English ''loc'', related to German ''loch'', "hole". History There are padlocks dating to the Roman Era, 500 BC – 300 AD. They were known in early times by merchants traveling the ancient trade routes to Asia, including China. Padlocks have been used in Europe since the middle La Tène period, subsequently spreading to the Roman world and the Przeworsk and Chernyakhov cultures.Katarzyna Czarnecka, "Padlocks In The Przeworsk And The Chernyakhov Cultures In The Late Roman Period, As An Evidence Of Mutual Contacts." Roman padlocks had a long bent rod attached to the case, and a shorter piece which could be inserted into the case. Przeworsk and Chernyak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of two solid surfaces in contact. Dry friction is subdivided into ''static friction'' ("stiction") between non-moving surfaces, and ''kinetic friction'' between moving surfaces. With the exception of atomic or molecular friction, dry friction generally arises from the interaction of surface features, known as asperities (see Figure 1). *Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. *Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. *Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. *Internal friction is the force resisting motion between the elements making up a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermal Conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. For instance, metals typically have high thermal conductivity and are very efficient at conducting heat, while the opposite is true for insulating materials like Rockwool or Styrofoam. Correspondingly, materials of high thermal conductivity are widely used in heat sink applications, and materials of low thermal conductivity are used as thermal insulation. The reciprocal of thermal conductivity is called thermal resistivity. The defining equation for thermal conductivity is \mathbf = - k \nabla T, where \mathbf is the heat flux, k is the thermal conductivity, and \nabla T is the temperature gradient. This is known as Fourier's Law for heat conduction. Although commonly expressed as a scalar, the most general form of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Conductivity
Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows electric current. Resistivity is commonly represented by the Greek letter (rho). The SI unit of electrical resistivity is the ohm- meter (Ω⋅m). For example, if a solid cube of material has sheet contacts on two opposite faces, and the resistance between these contacts is , then the resistivity of the material is . Electrical conductivity or specific conductance is the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current. It is commonly signified by the Greek letter ( sigma), but (kappa) (especially in electrical engineering) and (gamma) are sometimes used. The SI unit of electrical conductivity is siemens per metre (S/m). Resistivity and conductivity are inte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Milling (machining)
Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying direction on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of different operations and machines, on scales from small individual parts to large, heavy-duty gang milling operations. It is one of the most commonly used processes for machining custom parts to precise tolerances. Milling can be done with a wide range of machine tools. The original class of machine tools for milling was the milling machine (often called a mill). After the advent of computer numerical control (CNC) in the 1960s, milling machines evolved into ''machining centers'': milling machines augmented by automatic tool changers, tool magazines or carousels, CNC capability, coolant systems, and enclosures. Milling centers are generally classified as vertical machining centers (VMCs) or horizontal machining centers (HMCs). The integ ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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