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Riot Protection Helmet
A riot protection helmet or riot helmet is a type of helmet designed for law enforcement and military use to protect the wearer's head, face and eyes from handheld melee weapons, and thrown projectiles such as bricks, as may be met in riot control. Many modern riot squad helmets are reinforced with materials that will protect the wearer from dangerous substances such as acids or industrial chemicals. The riot protection helmets are usually made to be able to easily fit a gas mask, especially when tear gas is being used. There have been rare cases of riot protection helmets being worn to protect against objects blown by tornadoes or fierce storms, for example in England in the 18 January 2007 gale. Description The simplest form is a hard shell with reinforced padding, and a chinstrap and a hinge-up (usually polycarbonate) visor, as in this image. These riot protection helmet visors are usually curved sideways and straight up-and-down, not curved both ways like on the older type ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Visor
A visor (also spelled vizor) is a surface that protects the eyes, such as shading them from the sun or other bright light or protecting them from objects. Nowadays many visors are transparent, but before strong transparent substances such as polycarbonate were invented, visors were opaque like a mask. * The part of a helmet in a suit of armor that protects the eyes. *A type of headgear consisting only of a visor and a band as a way to fasten it around the head. *Any such vertical surface on any hat or helmet. *Any such horizontal surface on any hat or helmet (called a '' peak'' in British English). *A device in an automobile A car, or an automobile, is a motor vehicle with wheels. Most definitions of cars state that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, peopl ... that the driver or front passenger can lower over part of the windshield to block the sun ( sun visor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Law Enforcement Uniforms
Law is a set of rules that are created and are enforceable by social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and as the art of justice. State-enforced laws can be made by a legislature, resulting in statutes; by the executive through decrees and regulations; or by judges' decisions, which form precedent in common law jurisdictions. An autocrat may exercise those functions within their realm. The creation of laws themselves may be influenced by a constitution, written or tacit, and the rights encoded therein. The law shapes politics, economics, history and society in various ways and also serves as a mediator of relations between people. Legal systems vary between jurisdictions, with their differences analysed in comparative law. In civil law jurisdictions, a legislature or other central body codifies and consolidates the law. In common law systems, judge ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Earpiece
An in-ear monitor (IEMs), in-ear, or colloquially earpiece is a listening device placed into the ear. More narrowly, the term in-ear monitor is defined as such a device used by musicians, audio engineers and audiophiles to listen to music or to hear a personal mix of vocals and stage instrumentation for live performance or recording studio mixing, often specifically in order to hear themselves through a sound system in real time. They are also used by television presenters to receive vocal instructions, information and breaking news announcements from a producer that only the presenter hears. They are often custom-fitted to an individual's ears to provide comfort and a high level of noise reduction from ambient surroundings. Their origins as a tool in live music performance can be traced back to the mid-1980s. A stage monitor system is any system that provides a mix of audio sources to a performer on stage. Traditionally, loudspeakers were placed on the stage directed toward th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microphone
A microphone, colloquially called a mic (), or mike, is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public events, motion picture production, live and recorded audio engineering, sound recording, two-way radios, megaphones, and radio and television broadcasting. They are also used in computers and other electronic devices, such as mobile phones, for recording sounds, speech recognition, Voice over IP, VoIP, and other purposes, such as Ultrasonic transducer, ultrasonic sensors or knock sensors. Several types of microphone are used today, which employ different methods to convert the air pressure variations of a sound wave to an electrical signal. The most common are the dynamic microphone, which uses a coil of wire suspended in a magnetic field; the condenser microphone, which uses the vibrating Diaphragm (acoustics), diaphragm as a capacitor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radio
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates the waves. They can be received by other antennas connected to a radio receiver; this is the fundamental principle of radio communication. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications. In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking, and satellite communication, among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. In radar, used to locate and track ob ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brass
Brass is an alloy of copper and zinc, in proportions which can be varied to achieve different colours and mechanical, electrical, acoustic and chemical properties, but copper typically has the larger proportion, generally copper and zinc. In use since prehistoric times, it is a substitutional alloy: atoms of the two constituents may replace each other within the same crystal structure. Brass is similar to bronze, a copper alloy that contains tin instead of zinc. Both bronze and brass may include small proportions of a range of other Chemical element, elements including arsenic, lead, phosphorus, aluminium, manganese and silicon. Historically, the distinction between the two alloys has been less consistent and clear, and increasingly museums use the more general term "list of copper alloys, copper alloy". Brass has long been a popular material for its bright gold-like appearance and is still used for drawer pulls and door handle, doorknobs. It has also been widely used to ma ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Motorcycle Helmet
A motorcycle helmet is a type of helmet used by motorcycle riders. Motorcycle helmets contribute to motorcycle safety by protecting the rider's head in the event of an impact. They reduce the risk of head injury by 69% and the risk of death by 42%. Their use is required by law in many countries. However, only 10.4% of all motorcyclists wear helmets, according to the World Health Organization in 2016. Motorcycle helmets consist of a Polystyrene, polystyrene foam inner shell that absorbs the shock of an impact, and a protective plastic outer layer. Several variations exist, notably helmets that cover the chin area and helmets that do not. Some helmets provide additional conveniences, such as ventilation, face shields, sun visors, ear protection, or a wireless microphone. Origins The origins of the crash helmet date back to the Brooklands race track in early 1914, when a medical officer, Dr. Eric Gardner, noticed he was seeing a motor cyclist with head injuries about every two we ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Polycarbonate
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transparent. They are easily worked, injection molding, molded, and thermoforming, thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates do not have a unique resin identification code, resin identification code (RIC) and are identified as "Other", 7 on the RIC list. Products made from polycarbonate can contain the precursor monomer bisphenol A (BPA). Structure Carbonate esters have planar OC(OC)2 cores, which confer rigidity. The unique O=C bond is short (1.173 Å in the depicted example), while the C-O bonds are more ether-like (the bond distances of 1.326 Å for the example depicted). Polycarbonates received their name because they are polymers containing carbonate ester, carbonate groups (−O−( ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Helmet
A helmet is a form of protective gear worn to protect the head. More specifically, a helmet complements the skull in protecting the human brain. Ceremonial or symbolic helmets (e.g., a policeman's helmet in the United Kingdom) without protective function are sometimes worn. Soldiers wear combat helmets, often made from Kevlar or other lightweight synthetic fibers. The word ''helmet'' is derived from ''helm'', an Old English word for a protective head covering. Helmets are used for most sports (e.g., jockeys, American football, ice hockey, cricket, baseball, skiing, hurling and rock climbing); dangerous work activities such as construction, mining, riot police, military aviation, and in transportation (e.g. motorcycle helmets and bicycle helmets). Since the 1990s, most helmets are made from resin or plastic, which may be reinforced with fibers such as aramids. Designs Some British gamekeepers during the 18th and 19th centuries wore helmets made of straw bound together wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PI2G 3F
The number (; spelled out as pi) is a mathematical constant, approximately equal to 3.14159, that is the ratio of a circle's circumference to its diameter. It appears in many formulae across mathematics and physics, and some of these formulae are commonly used for defining , to avoid relying on the definition of the arc length, length of a curve. The number is an irrational number, meaning that it cannot be expressed exactly as a ratio of two integers, although fractions such as \tfrac are commonly Approximations of π, used to approximate it. Consequently, its decimal representation never ends, nor repeating decimal, enters a permanently repeating pattern. It is a transcendental number, meaning that it cannot be a solution of an algebraic equation involving only finite sums, products, powers, and integers. The transcendence of implies that it is impossible to solve the ancient challenge of squaring the circle with a Compass-and-straightedge construction, compass and stra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
