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Topic Review
Space Shuttle Launch Countdown
The launch of Space Shuttle missions was governed by a countdown. Two clocks were maintained, the unofficial, but sometimes mentioned, L (launch) clock represented the time remaining before the scheduled launch in real time, and the more often referred to T (test) clock included several built-in holds where additional verifications were made. Built-in holds were extended if mission parameters allowed for additional checks or to correct issues. Launches of the Space Shuttle to the International Space Station did not allow for holds to be extended due to the launch window which was limited to no more than 10 minutes due to the 90 minute orbit period of the station and speed of Earth's rotation (913.6 miles per hour (1,470.3 km/h) at the Kennedy Space Center), which puts the launch pads 1,000 miles (1,600 km) east of the station on its next orbit.
  • 1.2K
  • 22 Nov 2022
Topic Review
Surface Passivation
Passivation, in physical chemistry and engineering, refers to coating a material so it becomes "passive", that is, less readily affected or corroded by the environment. Passivation involves creation of an outer layer of shield material that is applied as a microcoating, created by chemical reaction with the base material, or allowed to build by spontaneous oxidation in the air. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shield against corrosion. Passivation of silicon is used during fabrication of microelectronic devices. In electrochemical treatment of water, passivation reduces the effectiveness of the treatment by increasing the circuit resistance, and active measures are typically used to overcome this effect, the most common being polarity reversal, which results in limited rejection of the fouling layer.[clarification needed] When exposed to air, many metals naturally form a hard, relatively inert surface layer, usually an oxide (termed the "native oxide layer") or a nitride, that serves as a passivation layer. In the case of silver, the dark tarnish is a passivation layer of silver sulfide formed from reaction with environmental hydrogen sulfide. (In contrast, metals such as iron oxidize readily to form a rough porous coating of rust that adheres loosely and sloughs off readily, allowing further oxidation.) The passivation layer of oxide markedly slows further oxidation and corrosion in room-temperature air for aluminium, beryllium, chromium, zinc, titanium, and silicon (a metalloid). The inert surface layer formed by reaction with air has a thickness of about 1.5 nm for silicon, 1–10 nm for beryllium, and 1 nm initially for titanium, growing to 25 nm after several years. Similarly, for aluminium, it grows to about 5 nm after several years. Surface passivation refers to a common semiconductor device fabrication process critical to modern electronics. It is the process by which a semiconductor surface such as silicon is rendered inert, and does not change semiconductor properties when it interacts with air or other materials. This is typically achieved by thermal oxidation, in which the material is heated and exposed to oxygen. In a silicon semiconductor, this process allows electricity to reliably penetrate to the conducting silicon below the surface, and to overcome the surface states that prevent electricity from reaching the semiconducting layer. Surface passivation by thermal oxidation is one of the key features of silicon technology, and is dominant in microelectronics. The surface passivation process was developed by Mohamed M. Atalla at Bell Labs in the late 1950s. It is commonly used to manufacture MOSFETs (metal-oxide-semiconductor field-effect transistors) and silicon integrated circuit chips (with the planar process), and is critical to the semiconductor industry. Surface passivation is also critical to solar cell and carbon quantum dot technologies.
  • 3.8K
  • 22 Nov 2022
Topic Review
Inside GNSS
Inside GNSS is an international controlled circulation trade magazine owned by Gibbons Media and Research LLC. It covers space-based positioning, navigation and timing (PNT) technology for engineers, designers and policy-makers of global navigation satellite systems (GNSS). In the United States GNSS is identified mainly with the government-operated Navstar Global Positioning System (GPS). Insidegnss.com is a site of online news, events, digital newsletters and webinars, and archived magazine articles.
  • 551
  • 22 Nov 2022
Topic Review
Triumph I4
The Triumph Four Cylinder or Triumph I4 engine is a cast-iron overhead valve straight-four engine produced by Standard Triumph. Introduced in their Standard Eight in 1953, it was used in a wide range of Triumph vehicles, including the Triumph Herald, Triumph Spitfire and certain Dolomites.
  • 641
  • 22 Nov 2022
Topic Review
Areal Density (Computer Storage)
Areal density is a measure of the quantity of information bits that can be stored on a given length of track, area of surface, or in a given volume of a computer storage medium. Generally, higher density is more desirable, for it allows more data to be stored in the same physical space. Density therefore has a direct relationship to storage capacity of a given medium. Density also generally affects the performance within a particular medium, as well as price.
  • 2.4K
  • 22 Nov 2022
Topic Review
BMW M Coupe
The BMW M Coupe is a shooting-brake styled high-performance automobile produced by BMW. Only two generations of the M Coupe have been manufactured, the original E36/8 Z3 Coupe and the second generation E86 Z4 Coupe.
  • 783
  • 22 Nov 2022
Topic Review
Lumped Element Model
The lumped element model (also called lumped parameter model, or lumped component model) simplifies the description of the behaviour of spatially distributed physical systems into a topology consisting of discrete entities that approximate the behaviour of the distributed system under certain assumptions. It is useful in electrical systems (including electronics), mechanical multibody systems, heat transfer, acoustics, etc. Mathematically speaking, the simplification reduces the state space of the system to a finite dimension, and the partial differential equations (PDEs) of the continuous (infinite-dimensional) time and space model of the physical system into ordinary differential equations (ODEs) with a finite number of parameters.
  • 375
  • 22 Nov 2022
Topic Review
Woodworking Joints
Joinery is a part of woodworking that involves joining pieces of wood or lumber, to produce more complex items. Some wood joints employ fasteners, bindings, or adhesives, while others use only wood elements. The characteristics of wooden joints - strength, flexibility, toughness, appearance, etc. - derive from the properties of the materials involved and the purpose of the joint. Therefore, different joinery techniques are used to meet differing requirements. For example, the joinery used to construct a house can be different from that used to make puzzle toys, although some concepts overlap. In British English usage it is distinguished from carpentry which relates to structural timber work.
  • 2.1K
  • 22 Nov 2022
Topic Review
Zeppelin LZ 85
The LZ 85 was a World War I R-Class zeppelin of the German Navy with a total length of 198 metres (649 ft 7 in), allocated the tactical numbering L 45. LZ 85 carried out a total of 27 flights including 3 raids on England and 12 reconnaissance missions. LZ 85(LZ55) was also the numbering of the German zeppelin downed in Thessaloniki on 5th May 1916 by the British Navy HMS Agamemnon.
  • 568
  • 22 Nov 2022
Topic Review
Successive Approximation ADC
A successive approximation ADC is a type of analog-to-digital converter that converts a continuous analog waveform into a discrete digital representation via a binary search through all possible quantization levels before finally converging upon a digital output for each conversion.
  • 5.7K
  • 22 Nov 2022
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