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Topic Review
Interferometry
Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed causing the phenomenon of interference in order to extract information. Interferometry is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography, seismology, spectroscopy (and its applications to chemistry), quantum mechanics, nuclear and particle physics, plasma physics, remote sensing, biomolecular interactions, surface profiling, microfluidics, mechanical stress/strain measurement, velocimetry, and optometry.:1–2 Interferometers are widely used in science and industry for the measurement of small displacements, refractive index changes and surface irregularities. In most interferometers, light from a single source is split into two beams that travel different optical paths, then combined again to produce interference, however, under the some circumstances two incoherent sources can also be interfered. The resulting interference fringes give information about the difference in optical path length. In analytical science, interferometers are used to measure lengths and the shape of optical components with nanometer precision; they are the highest precision length measuring instruments existing. In Fourier transform spectroscopy they are used to analyze light containing features of absorption or emission associated with a substance or mixture. An astronomical interferometer consists of two or more separate telescopes that combine their signals, offering a resolution equivalent to that of a telescope of diameter equal to the largest separation between its individual elements.
  • 3.1K
  • 17 Nov 2022
Topic Review
BeiDou Navigation Satellite System
The BeiDou Navigation Satellite System (BDS) is a Chinese satellite navigation system. It consists of two separate satellite constellations. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites which since 2000 has offered limited coverage and navigation services, mainly for users in China and neighboring regions. Beidou-1 was decommissioned at the end of 2012. The second generation of the system, officially called the BeiDou Navigation Satellite System (BDS) and also known as COMPASS or BeiDou-2, became operational in China in December 2011 with a partial constellation of 10 satellites in orbit. Since December 2012, it has been offering services to customers in the Asia-Pacific region. In 2015, China started the build-up of the third generation BeiDou system (BeiDou-3) in the global coverage constellation. The first BDS-3 satellite was launched on 30 March 2015. As of January 2018, nine BeiDou-3 satellites have been launched. BeiDou-3 will eventually consist of 35 satellites and is expected to provide global services upon completion in 2020. When fully completed, BeiDou will provide an alternative global navigation satellite system to the United States owned Global Positioning System (GPS), and is expected to be more accurate than the GPS. It was claimed in 2016 that BeiDou-3 will reach millimeter-level accuracy (with post-processing), which is ten times more accurate than the finest level of GPS. According to China Daily, in 2015, fifteen years after the satellite system was launched, it was generating a turnover of $31.5 billion per annum for major companies such as China Aerospace Science and Industry Corp, AutoNavi Holdings Ltd, and China North Industries Group Corp.
  • 3.1K
  • 29 Nov 2022
Topic Review
D-10 Tank Gun
The D-10 is a Soviet 100 mm tank gun developed in late World War II. It originally equipped the SU-100 tank destroyers and was later selected for the T-55 tank, equipping these as late as 1979. On the T-55 the D-10 continues to be in active service in many countries.
  • 3.1K
  • 19 Oct 2022
Topic Review
LAN Switching
LAN switching is a form of packet switching used in local area networks (LAN). Switching technologies are crucial to network design, as they allow traffic to be sent only where it is needed in most cases, using fast, hardware-based methods. LAN switching uses different kinds of network switches. A standard switch is known as a layer 2 switch and is commonly found in nearly any LAN. Layer 3 or layer 4 switches require advanced technology (see managed switch) and are more expensive, and thus are usually only found in larger LANs or in special network environments.
  • 3.0K
  • 15 Nov 2022
Topic Review
Urban Wastewater Treatment in Greece
Although Greece has accomplished the wastewater infrastructure construction in a large extent, as 91% of the country’s population is already connected to urban wastewater treatment plants (WWTPs), many problems still need to be faced, such as the limited reuse of treated wastewater and of the surplus sludge (biosolids) produced, the relative higher energy consumption in the existing rather aged WWTPs infrastructure and the proper management of failing or inadequately designed septic tank/soil absorption systems, still in use in several (mostly rural) areas, lacking sewerage systems. Moreover, the wastewater treatment sector should be examined in the general framework of sustainable environmental development; therefore, Greece’s future challenges in this sector ought to be reconsidered. Thus, the review of Greece’s urban wastewater history, even from the ancient times, up to current developments and trends, will be shortly addressed. Noting also that the remaining challenges should be analyzed in respect to the country’s specific needs (e.g. interaction with the extensive tourism sector), as well as to the European Union’s relevant framework policies and to the respective international technological trends, aiming to consider the wastewater treatment plants (WWTPs) not only as sites for the treatment/removal of pollutants to prevent environmental pollution, but also as industrial places where energy is efficiently used (or even produced), resources’ content can be potentially recovered and reused (e.g. nutrients, treated water, biosolids) and the environmental sustainability is being overall practiced.
  • 3.0K
  • 04 Aug 2020
Topic Review
Permanent Magnet Linear Synchronous Motor
In high-end testing and manufacturing equipment, a trend exists whereby the traditional servo feed system with a ball screw and rotary motor will gradually be replaced by a direct drive system. The precision motion system driven by a permanent magnet linear synchronous motor (PMLSM) offers several advantages, including high speed, high acceleration, and high positioning accuracy. However, the operating precision of the feed device will be affected by the PMLSM robustness to nonlinear and uncertain disturbances, such as cogging force, friction, thermal effects, residual vibration, and load disturbance.
  • 3.0K
  • 29 Apr 2021
Topic Review
Ordnance QF 6-pounder
The Ordnance Quick-Firing 6-pounder 7 cwt,[note 1] or just 6-pounder, was a British 57 mm gun, serving during the Second World War as a primary anti-tank gun of both the British and United States Army (as the 57 mm Gun M1). It was also used as the main armament for a number of armoured fighting vehicles. Although designed before the start of the war, it did not reach service until the North African Campaign in April 1942. There, it replaced the 2-pounder as an anti-tank gun, allowing the 25-pounder gun-howitzer to revert to its intended artillery role.
  • 3.0K
  • 03 Nov 2022
Topic Review
Apple Fermented Products
Fermentation is a process of transforming one substance into another, carried out by microorganisms, such as bacteria and fungi, under certain circumstances, and which can occur under aerobic and/or anaerobic conditions.
  • 3.0K
  • 18 Mar 2021
Topic Review
Panel Van
A panel van (or panelvan) is a form of solid (rigid-bodied, non-articulated) van, smaller than a lorry or truck, without rear side windows. In the UK this body style is referred to as a "car-derived van" and in North American as a "sedan delivery" (while the term "panel van" or "cargo van" generally refers to larger, truck-based vans such as the Ford E-Series and Chevrolet Express). In Australia panel vans were a development of the Australian "ute" (utility), a variety of pickup, based on a car chassis, these often utilizing the floorpan of the station wagon model. In North America a two-door station wagon base was used with only front seats and steel sheet-metal panels in place of the rear and side windows. Panel vans are widely used in many parts of the world for transporting cargo. In some national usages it is distinct from a purpose-designed van in that it is based on the chassis of a family car design. In places where they are distinct from a "van", they have less cargo space but better agility and maneuverability, making them particularly suited for cities with narrow streets or heavy traffic.
  • 3.0K
  • 11 Nov 2022
Topic Review
Semaphore Telegraph
A semaphore telegraph is an early system of conveying information by means of visual signals, using towers with pivoting shutters, also known as blades or paddles. Information is encoded by the position of the mechanical elements; it is read when the shutter is in a fixed position. The most widely used system was invented in 1792 in France by Claude Chappe, and was popular in the late eighteenth to early nineteenth centuries. Lines of relay towers with a semaphore rig at the top were built within line-of-sight of each other, at separations of 5–20 miles (8.0–32.2 km). Operators at each tower would watch the neighboring tower through a spyglass, and when the semaphore arms began to move spelling out a message, they would pass the message on to the next tower. This system was much faster than post riders for conveying a message over long distances, and also had cheaper long-term operating costs, once constructed. Semaphore lines were a precursor of the electrical telegraph, which would replace them half a century later, and would also be cheaper, faster, and more private. The line-of-sight distance between relay stations was limited by geography and weather, and prevented the optical telegraph from crossing wide expanses of water, unless a convenient island could be used for a relay station. Modern derivatives of the semaphore system include flag semaphore (a flag relay system) and the heliograph (optical telegraphy using mirror-directed sunlight reflections).
  • 3.0K
  • 28 Nov 2022
Topic Review
Arms Industry
The arms industry, also known as the defense industry or the arms trade, is a global industry responsible for the manufacturing and sales of weapons and military technology. It consists of a commercial industry involved in the research and development, engineering, production, and servicing of military material, equipment, and facilities. Arms-producing companies, also referred to as arms dealers, defence contractors, or as the military industry, produce arms for the armed forces of states and civilians. Departments of government also operate in the arms industry, buying and selling weapons, munitions and other military items. An arsenal is a place where arms and ammunition are made, maintained and repaired, stored, or issued, in any combination, whether privately or publicly owned. Products include guns, artillery, ammunition, missiles, military aircraft, military vehicles, ships, electronic systems, night vision devices, holographic weapon sights, laser rangefinders, laser sights, hand grenades, landmines and more. The arms industry also provides other logistical and operational support. Stockholm International Peace Research Institute (SIPRI) estimated that 2012 military expenditures were roughly $1.8 trillion. This represents a relative decline from 1990 when military expenditures made up 4% of world GDP. Part of the money goes to the procurement of military hardware and services from the military industry. The combined arms sales of the top 100 largest arms-producing companies amounted to an estimated $395 billion in 2012 according to SIPRI. In 2004 over $30 billion were spent in the international arms trade (a figure that excludes domestic sales of arms). According to SIPRI, the volume of international transfers of major weapons in 2010–14 was 16 per cent higher than in 2005–2009. The five biggest exporters in 2010–2014 were the United States, Russia, China, Germany and France, and the five biggest importers were India, Saudi Arabia, China, the United Arab Emirates and Pakistan. Many industrialized countries have a domestic arms-industry to supply their own military forces. Some countries also have a substantial legal or illegal domestic trade in weapons for use by its citizens, primarily for self-defence, hunting or sporting purposes. Illegal trade in small arms occurs in many countries and regions affected by political instability. The Small Arms Survey estimates that 875 million small arms circulate worldwide, produced by more than 1,000 companies from nearly 100 countries. Contracts to supply a given country's military are awarded by governments, making arms contracts of substantial political importance. The link between politics and the arms trade can result in the development of what U.S. President Dwight D. Eisenhower described as a military-industrial complex, where the armed forces, commerce, and politics become closely linked, similarly to the European multilateral defence procurement. Various corporations, some publicly held, others private, bid for these contracts, which are often worth many billions of dollars. Sometimes, as with the contract for the international Joint Strike Fighter, a competitive tendering process takes place, with the decision made on the merits of the designs submitted by the companies involved. Other times, no bidding or competition takes place.
  • 3.0K
  • 19 Oct 2022
Topic Review
Centrifugal Fan
A centrifugal fan is a mechanical device for moving air or other gases in a direction at an angle to the incoming fluid. Centrifugal fans often contain a ducted housing to direct outgoing air in a specific direction or across a heat sink; such a fan is also called a blower, blower fan, biscuit blower, or squirrel-cage fan (because it looks like a hamster wheel). These fans increase the speed and volume of an air stream with the rotating impellers. Centrifugal fans use the kinetic energy of the impellers to increase the volume of the air stream, which in turn moves against the resistance caused by ducts, dampers and other components. Centrifugal fans displace air radially, changing the direction (typically by 90°) of the airflow. They are sturdy, quiet, reliable, and capable of operating over a wide range of conditions. Centrifugal fans are constant-displacement or constant-volume devices, meaning that, at a constant fan speed, a centrifugal fan moves a relatively constant volume of air rather than a constant mass. This means that the air velocity in a system is fixed even though the mass flow rate through the fan is not. Centrifugal fans are not positive-displacement devices and centrifugal fans have certain advantages and disadvantages when contrasted with positive-displacement blowers: centrifugal fans are more efficient, whereas positive-displacement blowers may have a lower capital cost. The centrifugal fan has a drum shape composed of a number of fan blades mounted around a hub. As shown in the animated figure, the hub turns on a driveshaft mounted in bearings in the fan housing. The gas enters from the side of the fan wheel, turns 90 degrees and accelerates due to centrifugal force as it flows over the fan blades and exits the fan housing.
  • 3.0K
  • 23 Oct 2022
Topic Review
ThinkCentre M Series
The M-series of desktops are part of Lenovo's ThinkCentre product line. Formerly an IBM brand, Lenovo acquired the ThinkCentre desktop brand following its purchase of IBM's Personal Computing Division (PCD) in 2005. Following its acquisition of IBM's PCD, Lenovo has released M-series desktops in multiple form factors, ranging from traditional tower, to small form factor, and all-in-ones (AIOs).
  • 3.0K
  • 02 Nov 2022
Topic Review
Waveguide (Electromagnetism)
In electromagnetics and communications engineering, the term waveguide may refer to any linear structure that conveys electromagnetic waves between its endpoints. However, the original and most common meaning is a hollow metal pipe used to carry radio waves. This type of waveguide is used as a transmission line mostly at microwave frequencies, for such purposes as connecting microwave transmitters and receivers to their antennas, in equipment such as microwave ovens, radar sets, satellite communications, and microwave radio links. A dielectric waveguide employs a solid dielectric rod rather than a hollow pipe. An optical fibre is a dielectric guide designed to work at optical frequencies. Transmission lines such as microstrip, coplanar waveguide, stripline or coaxial cable may also be considered to be waveguides. The electromagnetic waves in a (metal-pipe) waveguide may be imagined as travelling down the guide in a zig-zag path, being repeatedly reflected between opposite walls of the guide. For the particular case of rectangular waveguide, it is possible to base an exact analysis on this view. Propagation in a dielectric waveguide may be viewed in the same way, with the waves confined to the dielectric by total internal reflection at its surface. Some structures, such as non-radiative dielectric waveguides and the Goubau line, use both metal walls and dielectric surfaces to confine the wave.
  • 3.0K
  • 07 Oct 2022
Topic Review
Acer Aspire Laptops
Acer Aspire (stylized as Λspire or ΛSPIRE) is a series of personal computers by Acer Inc. aimed at the casual household user or for small business use. The Aspire series covers both desktop computers and laptops. Acer developed the series in order to cover from essentials to high performances. Many of the Aspire laptops, such as model 8920G, have built in Blu-ray drives, 5.1 audio outputs and transflective displays. Acer was the first to include these drives in laptops. Most Aspire laptops have water-resistant screens, such as the 1410 and the 5741 Z. In 2007, Acer introduced the Gemstone series that marked a milestone in the Acer Aspire line. As with many Windows laptops, different models may have different specification in different parts of the world.
  • 2.9K
  • 20 Oct 2022
Topic Review
Frying
Frying is one of the oldest unit operations to produce food products with a crisp texture, an aromatic flavour and a golden-brown colour. Deep-fried foods such as French fries, potato/veggie crisps are popular among consumers. Detailed insights into the frying process in terms of heat, mass (water and oil) and momentum transfers are outlined in this entry.
  • 2.9K
  • 28 Jul 2020
Topic Review
Variable-Pitch Propeller
A variable-pitch propeller or controllable-pitch propeller (CPP) is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can also create reverse thrust for braking or going backwards without the need to change the direction of shaft revolution.
  • 2.9K
  • 23 Nov 2022
Topic Review
Epoxides Cycloaddition for CO2 Utilization
In the present review (10.3390/pr8050548), CO2 cycloaddition can be seen as a reasonably competent alternative to CO2 transformation, offsetting the high value-added nature by extending material use defer CO2 back to the atmosphere when compared to commodities and fuels such as urea, methanol, and methane.
  • 2.9K
  • 27 Aug 2020
Biography
Firouz Naderi
Firouz Michael Naderi (Persian: فیروز نادری‎: Fīrouz Nāderi; born 1946) is an Iranian scientist who spent more than 30 years in various technical and executive positions at NASA's Jet Propulsion Laboratory (JPL) where he contributed to some of America's most iconic robotic space missions. He retired from NASA in 2016 and currently is a management consultant, an advisor to early-st
  • 2.9K
  • 15 Nov 2022
Biography
John Glenn
Colonel John Herschel Glenn Jr. (July 18, 1921 – December 8, 2016) was a United States Marine Corps aviator, engineer, astronaut, businessman, and politician. He was the first American to orbit the Earth, circling it three times in 1962. Following his retirement from NASA, he served from 1974 to 1999 as a Democratic United States Senator from Ohio. Before joining NASA, Glenn was a distinguis
  • 2.9K
  • 22 Nov 2022
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