MV Lizzonia

Lizzonia was a Empire F type coaster that was built in 1944 by Goole Shipbuilding & Repairing Ltd, Goole, United Kingdom as Empire Farouche for the Ministry of War Transport (MoWT). In 1946, she was sold and renamed "Lizzonia". She was re-engined in 1956 and sank in 1961 following a collision with another vessel.
Description.
The ship was built in 1944 by Goole Shipbuilding & Repairing Ltd, Goole, East Riding of Yorkshire. She was yard number 3.
The ship was long, with a beam of . She had a draught of . She was assessed at , , 430DWT.
As built, the ship was propelled by a four-stroke Single Cycle, Single Action diesel engine, which had seven cylinders of 8¾ inches (22 cm) diameter by 11½ inches (30 cm) stroke driving a screw propeller. The engine was built by Blackstone & Co, Stamford, Lincolnshire.
History.
"Empire Farouche" was laid down by Goole Shipbuilding & Repairing Ltd, Goole, Yorkshire as "CHANT 35" and was renamed "Fabric 35" whilst under construction. She was launched as "Empire Farouche" on 19 September 1944 and completed in October 1944. The Code Letters MLZY and United Kingdom Official Number 180125 were allocated. Her port of registry was Goole. She was operated under the management of J Wharton (Shipping) Ltd.
"Empire Farouche" was built for the MoWT and was placed under the management of J Wharton (Shipping) Ltd. In 1946, she was sold to her managers and renamed "Lizzonia". A new diesel engine was fitted in 1956. On 16 March 1961, during foggy weather, "Lizzonia" was in collision with the Swedish cargo ship in the English Channel, west north west of the "Varne Lightship". Her crew was able to transfer to "Arctic Ocean" whilst the two ships were locked together. "Lizzonia" subsequently sank.


Barrett M99

The Barrett Model 99 "Big Shot" is a single-shot anti-materiel precision rifle that was first introduced in 1999 by the Barrett Firearms Company as a less expensive alternative to the company's higher-priced offerings. The rifle uses a bullpup single-shot configuration with a pistol grip. This Barrett Firearms Company is known for its .50 caliber rifles, including the M82A1 magazine-fed semi-automatic rifle.
Design.
The Model 99 rifle is a single shot bullpup rifle that debuted in 1999. Its primary market was long range competitive target shooters and in 2001 a shooter set a world record at 1,000-yards with the M99 by shooting a 5-shot group which measured 4.09″. The M99 features a hard-core construction, 7000 series aluminum alloy extrusion, match-quality trigger design, heat-treated steel M1913 rail, match grade barrel, and S-7 tool steel bolt. It has three quick assembly pins, allowing it to be assembled or disassembled without the use of tools. The Model 99 is very accurate because of its heavy contour barrel. With the .416 round, the accuracy and increased velocity compared to .50 BMG enables greater long range precision. The bolt is machined from a single piece of S-7 tool steel. To make the rifle very reliable and easy to maintain, the Model 99 has just three moving parts: the extractor, ejector and firing pin assembly. For bench rest shooting, the bi-pod can be detached easily. The design of the trigger is virtually maintenance free. The barrel is locked into the extrusion by being hydraulically pressed, allowing the user to mount a rifle scope on it. The steel gun barrel and the aluminum extrusion surround the cartridge, making the firearm safer.
Variants.
The rifle is offered in two calibers: .416 Barrett and .50 BMG. The .416 Barrett version is available with a 32" barrel and the .50 BMG version is available with a 29" or 32" barrel. Barrett also designs and makes a QDL suppressor for the Model 99. The 360 degree welding on the dual layered heat treated high strength alloys makes it the safest large bore suppressor on the market. The suppressor slides over the muzzle brake directly into the index point, allowing accurate alignment. The recoil of suppressed fire is reduced using an auxiliary two-port muzzle brake.


Magnetotaxis

Magnetotaxis is a process implemented by a diverse group of gram negative bacteria that involves orienting and coordinating movement in response to Earth's magnetic field. This process is mainly carried out by microaerophilic and anaerobic bacteria found in aquatic environments such as salt marshes, seawater, and freshwater lakes. By sensing the magnetic field, the bacteria are able to orient themselves towards environments with more favourable oxygen concentrations. This orientation towards more favourable oxygen concentrations allows the bacteria to reach these environments faster as opposed to if the bacteria were to move randomly to find these environments through Brownian motion. After orienting, the bacteria use flagella to swim along the magnetic field, towards the more favourable environment. Magnetotaxis has no impact on the average speed of the bacteria. Once these bacteria die, they are able to orient themselves to the Earth's magnetic field but they are incapable of migrating along the field. These bacteria are now simply called magnetic bacteria.
Magnetic bacteria (e.g. "Magnetospirillum magnetotacticum") contain internal structures known as magnetosomes which are responsible for the process of magnetotaxis. Magnetosomes contain crystals - often magnetite (Fe3O4). Some extremophile bacteria from sulfurous environments have been isolated with greigite (an iron-sulfide compound Fe3S4). Some magnetotactic bacteria also contain pyrite (FeS2) crystals, possibly as a transformation product of greigite. These crystals are contained within a bilayer membrane called the magnetosome membrane which is embedded with specific proteins. There are many different shapes of crystals however, crystal shape is usually consistent within a bacterial species. Most common arrangement of magnetosomes is in chains which allows a maximum magnetic dipole moment to be created. Within bacteria, there can be many chains of magnetosomes of different lengths that tend to align along the long axis of bacterial cell. The dipole moment created from the chains of magnetosomes allows the bacteria to align with the magnetic field as they move.
By orienting towards the Earth's poles, marine bacteria are able to direct their movement downwards, towards the anaerobic/micro aerobic sediments. In the northern hemisphere, north seeking bacteria move downwards while in the southern hemisphere, south seeking bacteria dominate and move downwards. It was originally thought by scientists that south seeking bacteria would move upwards in the north hemisphere, towards very high concentrations of oxygen, and will be negatively selected for so that north seeking bacteria dominate in the northern hemisphere and vice versa. However, south seeking bacteria have been found in the northern hemisphere. Also, magnetic bacteria, both north and south seeking, are found even at the Earth's magnetic equator, where the field is directed horizontally. Some aspects of magnetotaxis are still not completely understood.


.38 ACP

The .38 ACP (Automatic Colt Pistol), also known as the .38 Auto or 9x23mmSR, is a semi-rimmed pistol cartridge that was introduced at the turn of the 20th century for the John Browning-designed Colt M1900. It was first used in Colt's Model 1897 prototype, which he did not produce. The metric designation for the round is 9×23mm SR (semi-rimmed), which is not to be confused with other 9×23mm cartridges.
History.
Initial loadings of this cartridge were quite powerful. Reported ballistics for the first commercial loads were a 130-grain bullet at , and some experimental loads ran as high as . However, these ballistics proved too violent for the Colt Model 1900 pistol, and velocities were soon lowered to below . Subsequent commercial loadings varied considerably in power. For example, Hugh B.C. Pollard, writing in "Automatic Pistols" in 1920, gives Winchester factory ballistics for a 130-grain bullet at muzzle velocity and of muzzle energy; for Ely ammo, the figures for a 128-grain bullet were and and for Kynoch a 130-grain bullet . Later U.S. commercial loads in this caliber had factory standard ballistics of a 130-grain bullet at from the barrel of the Colt 1903 Pocket Model.
With Army Ordnance favoring a return to a .45 caliber sidearm by the time the Colt autos in .38 ACP were introduced, the caliber never gained much popularity. However, they did see small but steady sales up until the introduction of the more powerful .38 Super, which was little more than the .38 ACP loaded back to its original ballistics.
Sales of .38 ACP ammunition enjoyed a modest spike during the surplus gun boom of the 1950s and 1960s, since the cartridges would usually cycle in Spanish surplus pistols like the Astra 400 that were chambered for the 9×23mm Largo, despite the fact that the .38 ACP was semi-rimmed and slightly shorter than the rimless 9mm Largo. Some Astra 400 pistols were stamped "9M/M&38" on the barrel, denoting that the barrel was specifically designed to chamber both 9mm Largo and .38 ACP.
Europe would eventually favor the 9×19mm Parabellum cartridge. This cartridge is ballistically similar to the .38 ACP but utilizes a smaller case and higher pressures.
Browning himself was not done with 9 mm cartridges and introduced the 9mm Browning Long in 1903 and the .380 ACP in 1908.
.38 Super.
.38 Super was introduced in 1929, as a higher pressure loading of the .38 ACP. Even though .38 ACP and .38 Super are the same size, it is dangerous to use the more powerful .38 Super ammunition in a firearm intended for .38 ACP, as firearm damage may result. In the interest of safety, American ammunition companies formerly loaded .38 Super ammunition in nickeled cases exclusively. Since 1974, .38 Super cartridges have been marked with the +P markings used for greater pressure loads.
Firearms chambered for .38 ACP.
Notable firearms chambered for this cartridge include:


Stoletov curve

Stoletov curve shows the dependence of the magnetic permeability formula_1 of ferromagnetics on the intensity of the applied magnetic field "H". The curve is named after physicist Aleksandr Stoletov who analyzed in a long series of experiments the magnetic properties of iron rings in the period 1871–1872 during his stay at the Physical Laboratory of the University of Heidelberg.


Moulder


Kyle Spangler (schooner)

The Kyle Spangler was a wooden schooner; its 1860 wreck site in Lake Huron was listed on the National Register of Historic Places in 2016.
History.
Basil L. Spangler, born in 1817, was a dry-goods merchant from Cleveland who ran his own form, B. L. Spangler and Company. In 1856, Spangler commissioned William Jones, a shipbuilder from Black River Ohio (now Lorain), to construct a schooner. The schooner was named "Kyle Spangler", after Spangler's son, born in 1851. The ship was launched on May 12, 1856, and departed Cleveland with a cargo of coal two days later.
The "Spangler" was a traditional mid-nineteenth century cargo schooner that hauled various cargoes on the freshwater Great Lakes, and on to saltwater ports along the east coast. including iron ore, salt, coal, corn and wheat.
Like many schooners of the time, the "Spangler" endured a series of shipping incidents. In May 1856 she tore a hole in her bottom on a reef in Lake Huron. In 1857, she spring a leak in Lake Michigan, and was run aground just south of Sleeping Bear Bay before she sank. It was almost a year before she was refloated. The ship was dismasted in 1858, and later that same year collided with another schooner in the Straits of Mackinac. In 1859, the "Spangler" sailed into the Atlantic Ocean with a load of lumber, and returned the following spring.
On November 5, 1860, while upbound on Lake Huron on a dark night with a load of corn, the "Spangler" collided with the downbound schooner "Racine", crushing the "Spangler's" bow and sinking her. All crewmen were rescued safely.
The wreck.
The wreck was discovered in 2003 by diver Stan Stock while searching for the semi-whaleback freighter "Choctaw". Over the next few years, Stock and a team from the National Oceanic and Atmospheric Administration’s Thunder Bay National Marine Sanctuary documented the wreck. In 2008, it was decided to release the location of the wreck to the general public, and the location has become a popular scuba diving attraction.
The "Kyle Spangler" lies upright in 185 feet (56.4 meters) of water, and much of the wreck is undamaged save the bow. The cold, fresh water of Lake Huron has kept the wreck well preserved, and the ship looks much as she did during the 1850s, with both masts (including crosstrees) intact and upright. The wreck lists twenty degrees to the starboard side.
The ship's wheel, steering gear and rudder are intact, as are two bilge pumps and the main winch and capstan. The interior cabin structure is relatively intact, but the woodwork has collapsed, making small items difficult to discern. The cargo hold hatch covers are displaced, giving easy access to the hold.


420th Flight Test Squadron


.950 JDJ

The .950 JDJ (24.1x70mm) is a powerful large caliber rifle cartridge developed by American gunsmith and weapon designer J. D. Jones of SSK Industries.
Cartridge.
.950 JDJ cases are approximately 70 mm in length, and are based on a 20×110mm case shortened and necked up to accept the bullet. Projectiles are custom-made and most commonly weigh which is 8.2 ounces or over half a pound.
Rifles.
As its name implies, rifles chambered for the cartridge have a groove diameter of . SSK received a "Sporting Use Exception" to de-regulate the rifles. Thus, in the United States, they can be owned like any other Title I rifle by an American citizen at age 18. The rifles use McMillan Firearms stocks and extraordinarily thick Krieger barrels bearing an muzzle brake. Overall, depending on options, the rifles weigh from and are therefore only useful for shooting from a bench rest or heavy bipod. Despite the weight, recoil is significant and shooters must be sure to choose components (i.e., scopes and bipods) that can handle the force. The sheer size, weight, and power of these rifles make them rather impractical for hunting use. SSK only manufactured three of these rifles and as of 2014 no longer produces the ammunition.
Ballistics.
The cartridge propels its bullet at approximately . This yields a muzzle energy of .
By comparison, the 5.56×45mm NATO cartridge, used in the M16 and M4 rifles, produces between , while the .308 Winchester, a favorite for hunters and medium-range police/military sniping, produces between depending on the load used. Even the .50 BMG, which has a kinetic energy of around delivers less than half the energy. The ballistics of the .950 JDJ are more similar to that of the 20 mm autocannon round, which delivers approximately . The muzzle energy of the .950 JDJ is comparable to the kinetic energy of a automobile traveling at .
In a rifle, this will develop well over of free recoil energy. Shooting usually involves a heavy "lead sled" or similar shooting rest, and the rifle scope has significant eye relief to avoid injuring the ocular orbit.


79th Test and Evaluation Group


William W. Simmons (physicist)

William W. Simmons (born 1932) is An American physicist at TRW and Lawrence Livermore National Laboratory (LLNL), notable for his development of electro-optical devices.
Biography.
Simmons received his BA in Physics in 1953 from Carleton College and his MA in 1955 in Physics from University of Illinois at Urbana-Champaign, where in 1960 he also received his PhD in Physics.
After graduation he started at Space Technology Labs in the research and development of lasers and other electro-optic devices. Between 1968 and 1971 he returned to the Department of Engineering and Applied Science of the University of Illinois at Urbana-Champaign working as Associate Professor of electrical engineering. In 1972 he moved on to the Lawrence Livermore National Laboratory (LLNL), where he was project engineer in their new Laser Program. From 1985 till his retirement in 1992 he returned to TRW where he directed the research on "Solid State Lasers and Nonlinear Optics, Superconductive Electronics, and Semiconductor Diode Laser Devices and Arrays research groups."
Simmons was awarded the Distinguished Teaching in Engineering Award in 1972 from University of Illinois at Urbana-Champaign, and was awarded distinguished alumni in 2009 for his "outstanding original research contributions to the development of electro-optical devices, including pulsed ion lasers, very large laser systems, and semiconductor laser arrays, and for his leadership in furthering the national goal of fusion energy generation." In 1987 Simmons was awarded the IEEE Simon Ramo Medal for his "establishment and application of fundamental system design principles to the practical design and construction of very large solid-state laser facilities."


Taurus Model 608

The Taurus 608 was produced in 1997 in response to Smith & Wesson's .357 Model 686 Plus, which was chambered for seven rounds. Taurus re-chambered their large-frame 607 to hold eight rounds. This revolver was designed to achieve smooth trigger action.
Also, the rear sight is adjustable. It has factory porting for release of gases, reducing recoil. The Model 608 is available in three different barrel lengths. Scope mount bases are available to match the finish for the larger models.


Ivindomyrus opdenboschi

Ivindomyrus opdenboschi is a species of elephantfish in the family Mormyridae. It is only found in the Ivindo River in Gabon. It reaches a length of about .


Mach tuck

Mach tuck is an aerodynamic effect whereby the nose of an aircraft tends to pitch downward as the airflow around the wing reaches supersonic speeds. This diving tendency is also known as tuck under. The aircraft will first experience this effect at significantly below Mach 1.
Causes.
Mach tuck is usually caused by two things, a rearward movement of the centre of pressure of the wing and a decrease in wing downwash velocity at the tailplane both of which cause a nose down pitching moment. For a particular aircraft design only one of these may be significant in causing a tendency to dive, delta-winged aircraft with no foreplane or tailplane in the first case and, for example, the Lockheed P-38 in the second case. Alternatively, a particular design may have no significant tendency, for example the Fokker F28 Fellowship.
As an aerofoil generating lift moves through the air, the air flowing over the top surface accelerates to a higher local speed than the air flowing over the bottom surface. When the aircraft speed reaches its critical Mach number the accelerated airflow locally reaches the speed of sound and creates a small shock wave, even though the aircraft is still travelling below the speed of sound. The region in front of the shock wave generates high lift. As the aircraft itself flies faster, the shock wave over the wing gets stronger and moves rearwards, creating high lift further back along the wing. This rearward movement of lift causes the aircraft to tuck or pitch nose-down.
The severity of Mach tuck on any given design is affected by the thickness of the aerofoil, the sweep angle of the wing, and the location of the tailplane relative to the main wing.
A tailplane which is positioned further aft can provide a larger stabilizing pitch-up moment.
The camber and thickness of the aerofoil affect the critical Mach number, with a more highly curved upper surface causing a lower critical Mach number.
On a swept wing the shock wave typically forms first at the wing root, especially if it is more cambered than the wing tip. As speed increases, the shock wave and associated lift extend outwards and, because the wing is swept, backwards.
The changing airflow over the wing can reduce the downwash over a conventional tailplane, promoting a stronger nose-down pitching moment.
Another problem with a separate horizontal stabiliser is that it can itself achieve local supersonic flow with its own shock wave. This can affect the operation of a conventional elevator control surface.
Aircraft without enough elevator authority to maintain trim and fly level can enter a steep, sometimes unrecoverable dive. Until the aircraft is supersonic, the faster top shock wave can reduce the authority of the elevator and horizontal stabilizers.
All transonic and supersonic aircraft experience Mach tuck.
Recovery.
Recovery is sometimes impossible in subsonic aircraft; however, as an aircraft descends into lower, warmer, denser air, control authority (meaning the ability to control the aircraft) may return because drag tends to slow the aircraft while the speed of sound and control authority both increase.
To prevent Mach stall from progressing, the pilot should keep the airspeed below the type's critical Mach number by reducing throttle, extending speed brakes, and if possible, extending the landing gear.
Design features.
A number of design techniques are used to counter the effects of Mach tuck.
On both conventional tailplane and canard foreplane configurations, the horizontal stabiliser may be made large and powerful enough to correct the large trim changes associated with Mach tuck. In place of the conventional elevator control surface, the whole stabiliser may be made moveable or "all-flying", sometimes called a stabilator. This both increases the authority of the stabilizer over a wider range of aircraft pitch, but also avoids the controllability issues associated with a separate elevator.
Aircraft that fly supersonic for long periods, such as Concorde, may compensate for Mach tuck by moving fuel between tanks in the fuselage to change the position of the centre of mass to match the changing location of the centre of pressure, thereby minimizing the amount of aerodynamic trim required.
A Mach trimmer is a device which varies the pitch trim automatically as a function of Mach number to oppose Mach tuck and maintain level flight.
History.
 The fastest World War II fighters were the first aircraft to experience Mach tuck. Their wings were not designed to counter Mach tuck because research on supersonic airfoils was just beginning; areas of supersonic flow, together with shock waves and flow separation, were present on the wing. This condition was known at the time as compressibility burble and was known to exist on propeller tips at high aircraft speeds.
The P-38 was the first 400 mph fighter, and it suffered more than the usual teething troubles. It had a thick, high-lift wing, distinctive twin booms and a single, central nacelle containing the cockpit and armament. It quickly accelerated to terminal velocity in a dive. The short stubby fuselage had a detrimental effect in reducing the critical Mach number of the 15% thick wing center section with high velocities over the canopy adding to those on the upper surface of the wing. Mach tuck occurred at speeds above Mach 0.65; the air flow over the wing center section became transonic, causing a loss of lift. The resultant change in downwash at the tail caused a nose-down pitching moment and the dive to steepen (Mach tuck). The aircraft was very stable in this condition making recovery from the dive very difficult.
Dive recovery (auxiliary) flaps were added to the underside of the wing (P-38J-LO) to increase the wing lift and downwash at the tail to allow recovery from transonic dives.


Victor Togni

Victor Togni (March 1935 - 29 March 1965) was a Swiss Canadian organist, improviser, composer, and teacher. His compositions received positive reception. He won first prize at the American Guild of Organists' Improvisation Competition on June 26, 1964.
Career.
Togni was a church organist in several positions. In Italy, he served at San Gregorio Magno al Celio, Rome, and as the assistant to Fernando Germani, who was the organist of Saint Peter's Basilica in Vatican City. In Switzerland, he served at the Cathedral of Saint Lawrence, Lugano. He was the organist and choirmaster of St. Basil's Church and St. Michael's College, Toronto, at St. Michael's Cathedral Choir School as professor of organ and improvisation, as well as at St. Michael's Cathedral as organist.
In North America, he performed in concerts at St. Mary's Cathedral in Calgary, Saint Joseph's Cathedral in Edmonton, and Christ Church Cathedral in Vancouver, as well as the Wanamaker Organ in Philadelphia and the Cathedral of St. Paul in Minnesota. The concerts that he performed in Europe include the Cäcilienkirche in Regensburg, Germany. Togni performed at the Festival Internazionale di Musica Organistica di Magadino in Switzerland in 1963, where he played alongside Marcel Dupré and Gaston Litaize. The "Calgary Herald" wrote in 1964 that Togni was "an internationally-known organist". Before he died, Togni was scheduled to play at the Royal Canadian College of Organists' 1965 National Convention, and again at the same Magadino Festival in 1966. He was also slated for concerts at Haarlem, Rome, Paris, and throughout Germany.
The "Windsor Star" wrote in 1963 that Togni is a "world-renowned virtuoso" and that he "will improvise at length on a submitted theme - a rare and remarkable talent" at the University of Windsor. "Precomposed and Extemporized: Rediscovering the Life and Improvisatory Work of Canadian Organist Victor Togni (1935 - 1965)," a 2019 publication, assesses the role of improvisation in Togni's life, including unpublished recordings of Togni improvising. These improvisations largely date from the final years of Togni's life from 1963 to 1965, and include recordings of Togni's winning improvisation at the 1964 Improvisation Competition of the American Guild of Organists' National Convention at First Baptist Church, Philadelphia, as well as several improvised works on the historic former Warren and Son organ of St. Michael's Cathedral, Toronto, the Aeolian-Skinner organ of the Cathedral of St. Paul, Minnesota, and the Festival Internazionale di musica organistica di Magadino.
Personal life and death.
Togni was born in 1935 in what was later named Tanganyika in East Africa to Swiss parents.
In France, he studied with Rolande Falcinelli at the École Normale de Musique, with Olivier Messiaen at the Conservatoire National de Musique, and privately with Jean Langlais and Marcel Dupré. In Switzerland, he studied at Einsiedeln Abbey as a teenager; years later, he returned to Switzerland to study with Jean-Jacques Grunenwald at the Conservatoire de Musique de Genève, where he won three first prizes in organ. In Italy, he studied with the Italian organist Fernando Germani at the Accademia Nazionale di Santa Cecilia in Rome.
Togni was married in 1958 to Margaret. Their son Peter-Anthony Togni is also an organist.
Togni won first prize at the American Guild of Organists' Improvisation Competition on June 26, 1964. He won by improvising a prelude and fugue on themes by the American composer Vincent Persichetti. The prize was sponsored by Casavant Frères.
Togni was killed on March 29, 1965, in a car accident. He had been travelling to record an organ concert in Montreal, Québec.


Combo box

A combo box is a commonly used graphical user interface widget (or control). Traditionally, it is a combination of a drop-down list or list box and a single-line editable textbox, allowing the user to either type a value directly or select a value from the list. The term "combo box" is sometimes used to mean "drop-down list". In both Java and .NET, "combo box" is "not" a synonym for "drop-down list". Definition of "drop down list" is sometimes clarified with terms such as "non-editable combo box" (or something similar) to distinguish it from "combo box".


Hanna curve

Hanna curve - a curve defining magnetic parameters of an inductor.
Hanna curves help in finding optimum working conditions (maximum energy stored in an air gap) for an inductor. Several parameters are taken into account, including: magnetic field or flux density level, size of an air gap, physical dimensions of the magnetic core, number of turns of the winding, etc.


BNCR mount

BNCR is a lens mount developed by Mitchell for use with their REFLEX 35 mm movie cameras (long back-focus; Bausch & Lomb SUPER BALTARs, e.g., and equivalents). It was an update of the BNC mount (short back-focus; Bausch & Lomb BALTARs, e.g., and equivalents) done to accommodate the reflex viewer in the later cameras. BNC mount lenses cannot be used in reflex Mitchell cameras as their shorter back-focus will hit and damage the reflex viewer, which, in various versions, was a pellicle (partially silvered) mirror or a (100-percent silvered, first surface) rotating mirror. The abbreviation stands for "Blimped Newsreel Camera Reflex", which meant that it is a 35 mm camera originally intended for news reporting but included a blimp housing for sound stage shooting plus a reflex viewer to allow the camera operator to view the action through the lens while filming. The reflex option was only added in 1967, while the blimp option (thereby converting an NC, "Newsreel Camera", into a BNC, "Blimped Newsreel Camera") was available at the camera's introduction in 1934, but only a few BNC examples were made before the onset of WW-II, during which manufacture of "production" cameras was suspended.
The lens mount is not identical across all variants, thus there is a marked difference between a BNC and BNCR mount, for instance. BNCR is only the current convention as it was the last version of the camera and in relatively current use through until the 1990s. The mount contains four pronged flanges only one of which contains a notch towards the center. This notch is used to align the mount to a locating pin located approximately 45 degrees clockwise from the top of the camera's lens mount. This radial indexing is of particular importance when shooting an anamorphic format (CinemaScope or Panavision, or equivalent). The mount is locked into place using a friction locking ring which, in conjunction with the four prongs of the flange, creates a very strong lens seating. The quality of this design has been a key influence in the design of the Arri PL and Panavision PV mounts, both of which are the main film camera mounts in use today, and both of which have four-pronged flanges oriented based on locating pin-notch combinations. The Arri PL mount in particular is very similar in appearance to the BNCR mount, the only immediately apparent difference being the ability to seat any of the four notched prongs against the locating pin. (The flange focal distance and diameter also differ.)
With the slow obsolescence of the Mitchell cameras, which likely took so long because they were so well regarded in mechanical design aspects, such as their steady intermittent movement registration ("Compensating Link" movement) and strong mounts, the mounts have gradually become less common in the past two decades, but remained an option for third party cameras produced as recently as the 1980s. Many of the cameras are still in usage in fields such as animation. Though the mount is not quite as common today, it is still very well regarded in the field.


Crash cymbal

A crash cymbal is a type of cymbal that produces a loud, sharp "crash" and is used mainly for occasional accents, as opposed to a ride cymbal. It can be mounted on a stand and played with a drum stick, or by hand in pairs. One or two crash cymbals are a standard part of a drum kit. Suspended crash cymbals are also used in bands and orchestras, either played with a drumstick or rolled with a pair of mallets to produce a slower, swelling crash. Sometimes a drummer may hit two different crash cymbals in a kit at the same time to produce a very loud accent, usually in rock music.
Although crash cymbals range in thickness from paper-thin to very heavy, all crash cymbals have a fairly thin edge. They are typically in diameter, but sizes down to and up to are manufactured. Custom crash cymbals up to in diameter have been used by big bands. Different thicknesses are used for different kinds of music, and the alloy for each manufacturer's models varies. A thick cymbal is likely to be used by a metal or rock band, while thinner cymbals are generally used in lighter rock. Darker crashes are best used for jazz.
The sound of a crash is changed by its luster. A cleaner cymbal creates a crisper sound, whereas a cymbal showing signs of oxidation (called a 'raw' cymbal) creates a duller sound.
Normally, two crashes are best for a drum set; a 16" and a larger one.
Position.
Crash cymbals were traditionally placed on the left side of the drum set (for a right-handed drummer) since the normally larger ride cymbal is usually on the right, however some drummers set up their crash on the right. Often a drummer will have multiple crashes, and so may set them up with one or two on each side or, less commonly, one mounted very closely above another, usually larger crash or ride.
Crash cymbals are often the first ones in a drum set to warp and ultimately crack, due to repeated striking of the edge. Cracking is generally in the form of a fracture along the edge, or across the bow, often originating from the edge. Cracks are caused by poor technique or excessive playing or more rarely as a result of a defect originating from manufacture or damage to the cymbal not caused by playing, for example dropping. If a crack is left untreated, it will begin to follow the lathe grooves around the cymbal and could potentially spread all the way around and back to the point where it started, causing the outer portion of a cymbal to simply drop off. Often, lower quality sheet cymbals are more likely to crack, due to stress caused in some areas by pressing sheet metal. Thicker cymbals are also more likely to crack due to their brittleness and less freedom to vibrate. Cymbal manufacturers suggest that wear on the cymbal can be reduced by playing with glancing blows, angled to the side and slightly away from the vertical, about a quarter of the way between the edge and the center and allowing the drum stick to bounce off naturally, rather than forcing the stick down at the cymbal head-on. This allows the cymbal to vibrate freely and for little stress to be caused on the edge or at the center hole, thus reducing the chance of a crack. Cracked cymbals are often fixed either temporarily or permanently by drilling a hole at either end of the crack (often the crack will spread further than it appears to the naked eye, so this method is often not as effective) or removing the cracked portion or cutting the cymbal's edge down, although this method can drastically alter a cymbal's sound. Both of these methods are often ineffective at stopping cracks, but usually slow the spread of a crack down.
Orchestral crash cymbals.
A pair of identical crash cymbals held in both hands by leather thongs passing through holes in each cymbals bell is called clash cymbals and is a standard part of an orchestral percussion section. Two tones are normally used by major orchestras, known as "Germanic" or "Wagnerian" (heavier) and "Viennese" (lighter); a third, rarer tone is known as "French" (lighter still). Crash cymbals are also used in stage, concert, marching, and military bands.


Flexural rigidity

Flexural rigidity is defined as the force couple required to bend a fixed non-rigid structure by one unit of curvature, or as the resistance offered by a structure while undergoing bending.
Flexural rigidity of a beam.
In a beam or rod, flexural rigidity (defined as EI) varies along the length as a function of x shown in the following equation:
where formula_2 is the flexural modulus (in Pa), formula_3 is the second moment of area (in m4), formula_4 is the transverse displacement of the beam at x, and formula_5 is the bending moment at "x". If the material exhibits Isotropic behavior then the Flexural Modulus is equal to the Modulus of Elasticity (Young's Modulus).
Flexural rigidity has SI units of Pa·m4 (which also equals N·m²).
Flexural rigidity of a plate (e.g. the lithosphere).
In the study of geology, lithospheric flexure affects the thin lithospheric plates covering the surface of the Earth when a load or force is applied to them. On a geological timescale, the lithosphere behaves elastically (in first approach) and can therefore bend under loading by mountain chains, volcanoes and other heavy objects. Isostatic depression caused by the weight of ice sheets during the last glacial period is an example of the effects of such loading.
The flexure of the plate depends on:
As flexural rigidity of the plate is determined by the Young's modulus, Poisson's ratio and cube of the plate's elastic thickness, it is a governing factor in both (1) and (2).
Flexural Rigidity
formula_6
formula_2 = Young's Modulus
formula_8 = elastic thickness (~5–100 km)
formula_9 = Poisson's Ratio
Flexural rigidity of a plate has units of Pa·m3, i.e. one dimension of length less than the same property for the rod, as it refers to the moment per unit length per unit of curvature, and not the total moment. I is termed as moment of inertia. J is denoted as 2nd moment of inertia/polar moment of inertia.


Proceedings of the Institution of Mechanical Engineers, Part P

The Proceedings of the Institution of Mechanical Engineers, Part P: Journal of Sports Engineering and Technology is a peer-reviewed scientific journal that covers the development of novel sports apparel, footwear, and equipment; and the materials, instrumentation, and processes that make advances in sports possible. The journal was established in 2008 and is published by Sage Publications on behalf of the Institution of Mechanical Engineers.
Abstracting and indexing.
The journal is abstracted and indexed in Scopus and the Science Citation Index Expanded. According to the "Journal Citation Reports", its 2013 impact factor is 0.615.


Dynamite Nights Stunt Spectacular


The Screen Test Home Video Adventure


Paradise City station

Paradise City station ( "Paladaiseusiti Yeog") is a station of the Incheon Airport Maglev in Unseo-dong, Jung District, Incheon, South Korea. It was formerly known as International Business Center station ().


2874th Test Squadron


CZ 455

The CZ 455 is a series of magazine-fed bolt-action rimfire repeating rifle manufactured by the Czech firearms manufacturer Česká Zbrojovka Uherský Brod (abbreviated "CZ-UB", English: Czech Weapons Factory — Uherský Brod) and imported into the United States by CZ-USA. It is a successor of the highly popular CZ 452 rifles, and is chambered for the .22 LR (1:16" twist rate), .22 WMR (1:16" twist) and .17 HMR (1:9" twist) calibers.
The CZ 455 is produced with new manufacturing technology capable of closer tolerances for improved accuracy and smoother operation. All CZ 455s have hammer-forged, hand-lapped steel barrels, a trigger that is adjustable for weight of pull, and the capability to interchange barrels in different contours and calibers by simply removing two set screws from the receiver.
Design and operation.
Instead of the barrel being threaded into the receiver, as found on the CZ 452, all CZ 455 models use twin set-screws to fix the barrel in the frame as part of an interchangeable barrel system. Additionally, actions can be swapped into any 455 stock without modifications. All versions feature a milled 11 mm dovetail rail atop the receiver for the mounting of optical or telescopic sights.
History.
First introduced in 2010, the CZ 455 was designed to replace the CZ 452 series which is being phased out of current production. The CZ 452 first appeared in 1954 as the Model 2 (ZKM 452), and was a refinement of the CZ Model 1 (ZKM-451) .22-calibre rimfire bolt-action training rifle that first appeared in 1947. ZKM is an acronym for Zbrojovka-Koucký-Malorážka, the rifle's manufacturer ([Česká] Zbrojovka), designer (Josef Koucký) and Malorážka - for rimfire rifle). The Model 1 or ZKM-451 was developed on the request of the occupying German authority in 1943-44, when very few rifles were built as fully stocked Mauser 98k-type trainers. The receivers of these early .22 training rifles were marked "tgf" ("Tschechische Gewehr Fabrik" - German for Czech Rifle Factory) by the German Heereswaffenamt. Because of wartime requirements for combat weapons, assembly and production was halted on all .22 training rifles, leaving a large stockpile of parts and receivers at war's end. After the war, these parts (some of which still have the "tgf" code) were used along with new barrels and stocks to make the Model 1.
Versions.
CZ 455 Standard.
The CZ 455 Standard rimfire rifle corresponds in its construction to the CZ 455 Lux model, but comes with iron sights and a beechwood stock with a European-style down-leaning straight comb and no cheekpiece.
CZ 455 Scout.
The Scout features adjustable iron sights, integrated 11mm Dovetail iron sights. Barrel length is 16 inches; the stock is an American style beech wood with 12 inch length of pull. Total weight is 5 lbs.
CZ 455 FS.
Like the CZ 452 Standard, the CZ 455 FS has a full-length Mannlicher-style stock, open iron sights, and a Bavarian-style "hog-back" stock with increased drop and an arched cheekpiece. Barrel length is 525 mm, 2,7 kg.
CZ 455 Long.
The CZ 455 Long features a 24.8-inch (630mm) barrel, Bavarian-style Turkish walnut stock, and barrel-mounted tangent sights.
CZ 455 LUX.
The CZ 455 LUX has a lacquered stock made from Turkish walnut featuring checkering located on the pistol grip, and is primarily designed for use with open sights. The steel barrel is fitted with fully adjustable open sights. Barrel length is 20.67 inches (525 mm), weight is 6.17 lbs. (2,8 kg) unloaded.
CZ 455 LUX II.
The CZ 455 has a 24.8-inch (630 mm) long barrel with leaf sights and Bavarian-style Turkish walnut stock. Weight is 2,9 kg.
CZ 455 Super Match.
The CZ 455 Super Match has a 20.67-inch (525 mm) barrel with full-adjustable open sights and 12-groove rifling intended to improve accuracy. The Super Match comes with a 10-round magazine and a Bavarian-style "hog-back" stock designed primarily for use with open sights. Weight unloaded is 6.17 lbs (2,8 kg).
CZ 455 Ultra Match.
The Ultra Match features a 24.8-inch (630mm) barrel, Bavarian-style stock and barrel-mounted tangent sights adjustable for elevation. The CZ 455 barrel utilizes 12 groove rifling intended to increase accuracy.
CZ 455 Jaguar.
The CZ 455 Jaguar uses an unusually long 28.6-inch (726 mm) tapered barrel with rear tangent sight and a Bavarian-style stock.
CZ 455 American.
The CZ 455 American has a five-round polymer magazine and features an American-style levelled high-comb Turkish walnut stock designed solely for use with telescopic sights. The hammer-forged steel barrel is 20.67-inch (525 mm) long with a sporter contour.
CZ 455 Synthetic.
Based on the CZ 455 American, but is fitted with a synthetic composite stock.
CZ 455 Stainless.
Also known as CZ 455 Stainless Synthetic, it is based on the CZ 455 Synthetic, but fitted with stainless steel barrel and receiver.
CZ 455 Varmint.
The CZ 455 Varmint is fitted with a heavy-contour "bull" barrel designed to increase accuracy, and weighs . The Varmint uses the same high-comb Turkish walnut stock of 455 American, and is designed solely for use with telescopic sights.
CZ 455 Thumbhole.
Based on the CZ 455 Varmint, but fitted with a heavy laminated wood stock with a thumbhole grip. It also comes with yellow- and grey-colored versions.
CZ 455 Evolution.
The CZ 455 Evolution is a variant of the CZ 455 Varmint and features the standard Varmint barrelled action fitted inside a lightweight, blue-grey Boyd SS Evolution® laminated wood stock, and is primarily intended for target shooting. It also comes in a green-brown-grey "woodland" version called "Evolution GG". This model has been discontinued by CZ-USA, but still available via CZ-UB.
CZ 455 Varmint Tacticool.
The CZ 455 Varmint Tacticool is a variant of the CZ 455 Varmint and features the standard Varmint barrelled action fitted inside a black Boyd Pro Varmint® stock, with a Monte Carlo comb and a vertical grip, and is primarily intended for target shooting. In North America, CZ-USA offers the Tacticool in a barrel "Suppressor-Ready" version.
CZ 455 Varmint Precision Trainer.
The CZ 455 Varmint Precision Trainer is a variant of the CZ 455 Varmint only offered by CZ-USA. It features the standard Varmint barrelled action fitted inside a GAP camouflage-pattern Manners MCS-T4 22 Trainer stock, and is primarily intended for target shooting. In addition to the standard 20.5-inch barrel, CZ-USA also offers 16.5-inch and 24-inch threaded "Suppressor-Ready" versions.


Disk loading

In fluid dynamics, disk loading or disc loading is the average pressure change across an actuator disk, such as an airscrew. Airscrews with a relatively low disk loading are typically called rotors, including helicopter main rotors and tail rotors; propellers typically have a higher disk loading.
The V-22 Osprey tiltrotor aircraft has a high disk loading relative to a helicopter in the hover mode, but a relatively low disk loading in fixed-wing mode compared to a turboprop aircraft.
Rotors.
Disc loading of a hovering helicopter
is the ratio of its weight to the
total main rotor disc area. It is determined by dividing
the total helicopter weight by the rotor disc area,
which is the area swept by the blades of a rotor. Disc
area can be found by using the span of one rotor blade
as the radius of a circle and then determining the area
the blades encompass during a complete rotation. When a helicopter is being maneuvered, its disc loading changes.
The higher the loading, the more power needed to
maintain rotor speed. A low disc loading is a direct indicator of high lift thrust efficiency.
Increasing the weight of a helicopter increases disk loading. For a given weight, a helicopter with shorter rotors will have higher disk loading, and will require more engine power to hover. A low disk loading improves autorotation performance in rotorcraft. Typically, an autogyro (or gyroplane) has a lower rotor disc loading than a helicopter, which provides a slower rate of descent in autorotation.
Propellers.
In reciprocating and propeller engines, disk loading can be defined as the ratio between propeller-induced velocity and freestream velocity. Lower disk loading will increase efficiency, so it is generally desirable to have larger propellers from an efficiency standpoint. Maximum efficiency is reduced as disk loading is increased due to the rotating slipstream; using contra-rotating propellers can alleviate this problem allowing high maximum efficiency even at relatively high disc loadings.
The Airbus A400M fixed-wing aircraft will have a very high disk loading on its propellers.
Theory.
The "momentum theory" or "disk actuator theory" describes a mathematical model of an ideal actuator disk, developed by W.J.M. Rankine (1865), Alfred George Greenhill (1888) and R.E. Froude (1889). The helicopter rotor is modeled as an infinitely thin disc with an infinite number of blades that induce a constant pressure jump over the disk area and along the axis of rotation. For a helicopter that is hovering, the aerodynamic force is vertical and exactly balances the helicopter weight, with no lateral force.
The upward action on the helicopter results in a downward reaction on the air flowing through the rotor. The downward reaction produces a downward velocity on the air, increasing its kinetic energy. This energy transfer from the rotor to the air is the induced power loss of the rotary wing, which is analogous to the lift-induced drag of a fixed-wing aircraft.
Conservation of linear momentum relates the induced velocity downstream in the far wake field to the rotor thrust per unit of mass flow. Conservation of energy considers these parameters as well as the induced velocity at the rotor disk. Conservation of mass relates the mass flow to the induced velocity. The momentum theory applied to a helicopter gives the relationship between induced power loss and rotor thrust, which can be used to analyze the performance of the aircraft. Viscosity and compressibility of the air, frictional losses, and rotation of the slipstream in the wake are not considered.
Momentum theory.
For an actuator disk of area formula_1, with uniform induced velocity formula_2 at the rotor disk, and with formula_3 as the density of air, the mass flow rate formula_4 through the disk area is:
By conservation of mass, the mass flow rate is constant across the slipstream both upstream and downstream of the disk (regardless of velocity). Since the flow far upstream of a helicopter in a level hover is at rest, the starting velocity, momentum, and energy are zero. If the homogeneous slipstream far downstream of the disk has velocity formula_6, by conservation of momentum the total thrust formula_7 developed over the disk is equal to the rate of change of momentum, which assuming zero starting velocity is:
By conservation of energy, the work done by the rotor must equal the energy change in the slipstream:
Substituting for formula_7 and eliminating terms, we get:
So the velocity of the slipstream far downstream of the disk is twice the velocity at the disk, which is the same result for an elliptically loaded fixed wing predicted by lifting-line theory.
Bernoulli's principle.
To compute the disk loading using Bernoulli's principle, we assume the pressure in the slipstream far downstream is equal to the starting pressure formula_12, which is equal to the atmospheric pressure. From the starting point to the disk we have:
Between the disk and the distant wake, we have:
Combining equations, the disk loading formula_15 is:
The total pressure in the distant wake is:
So the pressure change across the disk is equal to the disk loading. Above the disk the pressure change is:
Below the disk, the pressure change is:
The pressure along the slipstream is always falling downstream, except for the positive pressure jump across the disk.
Power required.
From the momentum theory, thrust is:
The induced velocity is:
Where formula_22 is the disk loading as before, and the power formula_23 required in hover (in the ideal case) is:
Therefore, the induced velocity can be expressed as:
So, the induced velocity is inversely proportional to the power loading formula_26.


Zaragoza Corla

In 1956 brothers "José" and "Andrés", Zaragoza founded the "Zaragoza Arms Factory" in Mexico City, near Mexico City International Airport. The first weapon made by this outfit was a single-shot rifle .22 caliber.
Later, they started manufacturing the .22 caliber semiautomatic pistol Corla model, which was named in honor of two dealers who had the surnames Larios and Cordova. As for the brand logo, the letters H and Z correspond to "Hermanos Zaragoza".
Variants.
Short model.
The total length of this was 4 inches and featured engraving representing The Temple of the Sun at Teotihuacan and the volcanoes Popocatepetl and Iztaccihuatl. At the beginning of its production its planned name was "Azteca" in honor of the Aztecs, but the name was changed to "Corla" for the reasons explained above.
Long model.
The Long Model was designed due to recoil in the short model. It was decided to remove the engraving of the volcanoes and the pyramid. Total numbers manufactured were approximately 1150 units.
End of production.
Like most weapons factories in Mexico, this also disappeared after the student strike in 1968, as then-President Gustavo Díaz Ordaz made a decree to regulate firearms.


Regina Company

The Regina Company was a manufacturer of mechanical musical instruments before it became a major vacuum maker.
History.
In 1889, Gustave Brachhausen, the foreman of the Symphonion music box company based in Leipzig, created the polyphon Musikwerke in partnership with a Symphonion engineer Paul Riessner. Three years later, at the age of 35, Brachhausen expanded his enterprise to America by establishing the Regina Music Box Company. After sailing to America in September 1892, he leased some space in Jersey City, and with financing from Knauth, Nachod & Kuhne in Leipzig, Brachhausen set up shop in partnership with Riessner and Johannas J. Korner.
Initially, Regina imported their boxes from Polyphon, selling 11 and 15.5-inch models. Gradually, the movements were imported and assembled into American-made boxes. After a year of immediate success, Brachhausen purchased a 25,000-square foot building at 54 Cherry Street in Rahway. In a few years, Regina was manufacturing their products entirely in America, as Brachhausen accumulated patents. Regina established a nationwide distribution network by offering a 50% wholesale price to department stores and other retailers. He also lured one of Symphonion's arrangers, Octave Felicien Chaillet, to America, where he composed and arranged thousands of discs for Regina. In 1897, Brachhausen patented an automatic disc changer, and Regina established a service for installing and maintaining their coin-operated music boxes.
Regina boxes were seen as strong profit drivers partially because they created a steady revenue stream, as consumers would buy new discs to play on boxes they had already purchased. For a machine that cost $500, this was a relatively novel idea. Regina shipped 100,000 music boxes between 1892 and 1921, with sales topping out over $2 million a year. The company had 325 employees, and even as Symphonion established an American branch, Regina thrived as the market leader. Competition from the phonograph jeopardized the company in the early years of the 20th century, and in 1902, it dropped "Music Box" from its name and started to diversify. Its first vacuum cleaner was a two-person hand-pumped pneumatic model which sold poorly. In 1903, Knauth and company overtook the company to protect its investment, relegating Brachhausen to factory manager. New products continued to flood the market from the Regina company, everything from player pianos to copying presses. Eventually, the company went bankrupt in 1922.
The company introduced canister vacuum models in the 1930s. In 1952, Regina introduced its more familiar stick model, the ElectrikBroom. During World War II, the company made bomb fuses. In the 1980s, CEO Donald D. Sheelen led a group of employees who purchased Regina for $38 Million in a leveraged buyout. Don Sheelen’s inventions cross the vacuum sphere from the basic vacuum cleaner to the steam cleaner. During the 90s, the Peanuts character Pig-Pen appeared in commercials. The “tools on board” idea, “cyclonic” vacuum technology, and the modern easy to use steam cleaner were all the brainchild of Don Sheelen, who pled guilty to fraud in 1989 for falsifying company financial records. The Regina Company declared bankruptcy shortly thereafter and was eventually acquired by Philips Electronics in 1995. Oreck bought the company in 1997, and in 2000, it was sold to the Royal Corporation, the owners of the Dirt Devil brand, which sold the vacuums under the Home Depot brand for a few years. In 2020 Regina Vacuum LLC relaunched the Regina brand.
Major musical products.
Regina Music Box – Regina's music boxes were their original product, and they had an 80–90% share of the market at the company's peak. Regina music boxes use a flat metal disc, as opposed to a cylinder. Sizes ranged from 8.5 – 27 inches. The boxes were renowned for the rich tone, and they used a double set of tuned teeth.
Reginaphone – A response to the competition posed by the phonograph, the Reginaphone was a hybrid machine that played both music box discs and phonographs. Regina used a phonograph mechanism manufactured by the American Graphophone Company, which evolved into Columbia Records.
Coin Piano – Regina sold player pianos which were manufactured by other companies, sometimes putting German-made mechanisms into their own cases. One model was branded the "Reginapiano".
Concerto – The concerto used a 32-inch music box disc to control a player piano.
Phonograph – Regina branded several lines of phonographs, including the Hexaphone, Corona Talking Machine and Princess Phonographs.


Entertainment Computer System

The Entertainment Computer System (ECS) was an add-on peripheral for the Intellivision. It was Mattel Electronics' second attempt at creating a peripheral to upgrade the Intellivision into a home computer, and was rushed into production to appease the Federal Trade Commission after they began fining Mattel for false advertising following consumer complaints about the repeated delays in releasing the originally planned Intellivision Keyboard Component add-on. The ECS includes the Computer Module, Music Synthesizer, and additional hand controllers; each sold separately. Any Intellivision Master Component is compatible and a requirement to use the system. A second requirement is a cartridge plugged into the ECS, although any ECS or Intellivision cartridge will do; pressing anything on the Intellivision hand controllers will then bring up the three-option menu of BASIC, CARTRIDGE or MUSIC.
History.
When Mattel Electronics originally released the Intellivision in late 1979, they advertised that the Intellivision — unlike its primary rival, the Atari 2600 (then known as the Atari VCS) — would be upgradeable to a fully functional home computer via a hardware add-on accessory called the Keyboard Component, internally sometimes called the "Blue Whale" or the "Intelliputer". Many potential buyers were excited by the notion (especially parents, who liked the idea of a machine that could be turned into an educational tool, or at least something more useful and practical than just a game-playing system), and many bought Intellivisions on that basis alone.
The planned Keyboard Component would have offered a 16kB of RAM (expandable to an unprecedented 8 megabytes), built-in cassette storage for programs and data (plus a simultaneous audio track that could be played under computer control), an optional 40-column thermal printer, and a secondary CPU to run all of these expanded features independently of the Intellivision's CP1610 processor. Unfortunately, while the planned Keyboard Component was an ambitious design, it had some reliability problems that proved difficult to overcome, and it was far too expensive to manufacture and sell. The Keyboard Component — originally planned for a 1981 release — was continually delayed and pushed back as Mattel's engineering group, headed by David "Papa Intellivision" Chandler, kept going back to the drawing board trying to find ways to overcome these problems.
Eventually, complaints from Intellivision owners who had chosen to buy the Intellivision specifically on the promise of a "Coming Soon!" personal-computer upgrade caught the attention of the Federal Trade Commission (FTC), which launched an investigation of Mattel Electronics for fraud and false advertising. Mattel tried to claim that the Keyboard Component was a real product that was still being test-marketed, and even released a small number of Keyboard Components and a handful of software titles to a few select retail stores (as well as offering them via mail-order to any customers who complained loudly enough) in order to support this claim. The FTC was not impressed and finally, in mid-1982, imposed a fine of $10,000 per day until the promised computer upgrade was in full retail distribution.
Mattel Electronics already had a "plan B" in progress. Increasingly concerned that the Keyboard Component division might never actually produce a sellable product, in mid-1981 Mattel Electronics' management set up a competing internal engineering team headed by Richard Chang. Ostensibly, this group was working on a low-cost add-on called the BASIC Development System, or BDS, which would be sold as an educational device to introduce kids to the concepts of computer programming via a simplified color-coded BASIC interpreter and an inexpensive keyboard. Only a few people within Mattel knew the team's "real" mission: to either fix the Keyboard Component, or replace it.
Chang's "Design & Development" group (who had to keep the project's real purpose a closely guarded secret among themselves, fearing that if Chandler found out about it he would use his influence at Mattel, Inc. to get the project killed) eventually came up with an alternative to the Keyboard Component. Originally dubbed the LUCKI (from "Low User-Cost Keyboard Interface"), it lacked many of the sophisticated features envisioned for the original Keyboard Component: instead of a full 16kB of RAM, it only offered a mere 2kB (not all of which was actually available to the user); the cassette interface was stripped down to the bare essential needed to save and load data (and was now an optional extra, rather than built-in), and there was no secondary CPU. Still, it fulfilled the original promises—turn the Intellivision into a computer, make it possible to write programs and store them to tape, and interface with a printer—well enough to allow Mattel to claim that they had delivered the promised computer upgrade and, it was hoped, to get the FTC and its $10,000/day fine off Mattel's back.
On the plus side, the ECS "did" include a built-in BASIC that was somewhat functional, if idiosyncratic and occasionally buggy, and a second AY-3-8910 sound chip which expanded the system's audio capabilities to six-voice synthesized sound and, when paired with the optional 49-key Music Synthesizer keyboard, could potentially turn the Intellivision into a polyphonic synthesizer for playing, recording, or learning music. It would also allow two additional hand-held Game Controllers to be connected in place of the alphanumeric keyboard, which opened up the possibility of four-player games.
In the fall of 1982, the LUCKI—now renamed the Entertainment Computer System, or ECS—was presented at the annual sales meeting, officially signaling the end of the ill-fated Keyboard Component project. (Although it didn't go quietly. Not only did Mattel have to agree to buy back all of the existing Keyboard Components, but the manufacturer which had been contracted to make the Keyboards (Compro, Inc.) promptly sued Mattel for $10 million claiming breach of contract, fraud, and nonpayment for the last 1,300 units. At least a number were modified (and dubbed internally "Black Whales") to use as part of development systems for creation of Intellivision software.) A new advertising campaign was hastily rushed onto the air in time for the 1982 Christmas season, promising once again that a home-computer upgrade was just around the corner, and the ECS itself was shown to the public at the January 1983 Consumer Electronic Show (CES) in Las Vegas. A few months later, the ECS hit the market, and the FTC agreed to drop the $10K/day fines.
By the time the ECS made its retail debut, an internal shake-up at the top levels of Mattel Electronics' management had caused the company's focus to shift away from hardware add-ons in favor of software, and the ECS received very little further marketing push. Further hardware developments, including a planned Program Expander that would have added another 16kB of RAM and a more sophisticated, fully featured Extended-BASIC to the system, were halted, and in the end only a half-dozen titles were released for the ECS.
Games.
Initially, at least a half-dozen ECS-supporting software titles were slated to roll out along with the ECS, with more to follow. Unfortunately, as noted above, by the time the ECS made its retail debut in 1983 a new management team had taken over at Mattel Electronics which was no longer interested in selling or promoting hardware add-ons, which they viewed as money-losers that had tied up too much of the company's capital for too little return. (Perhaps not without some justification, given the history of the long-delayed, never-released Keyboard Component and the lower-than-expected sales of the Intellivoice module.) The Marketing and Applications departments were also not particularly enthusiastic about the ECS unit, since it really didn't add any revolutionary features to the system and it was a struggle to come up with game ideas that would justify requiring the user to have one.
As a result, the ECS was not well-promoted, and few of the planned software titles were released before Richard Chang's "Design & Development" group was closed down in August 1983, effectively halting further work on ECS-supporting titles. A very few titles that were already well in progress were eventually completed, but none of them made it to production before Mattel Electronics ceased operations in January 1984.
Released Titles.
"Melody Blaster" was the only title ever released for the Music Synthesizer add-on unit.
"Mr. BASIC Meets Bits 'N Bytes" plays without the ECS Computer Module with BASIC commands support disabled.
Unreleased Titles.
"Number Jumble" plays without the Computer Module.
"Super NASL Soccer" was eventually released as World Cup Soccer by Mattel Electronics' French division, which reformed under the name Nice Ideas when Mattel Electronics was shut down. "World Cup Soccer" was sold as a standard Intellivision cartridge but does support ECS 4-player with the Computer Adaptor and extra game controllers.
Keywords in ECS BASIC.
The BASIC keywords built into the ECS, discussed at length in the manual, are a maximum of four characters long. Some ECS BASIC keywords are simply a truncation or abbreviation of the standard BASIC terms, e.g. "print" becomes PRIN, "input" becomes INPU, and "gosub" becomes GSUB. The ECS will display help menus covering its commands: type MENU 0 for monitor commands, MENU 1 for BASIC keywords, MENU 2 for BASIC functions, and MENU 3 for BASIC routines.
Eight sprites at a time may be SHOWn or GRABbed from a storehouse of such images in each individual Intellivision cartridge, and such sprites can then be manipulated by changing their colors (1 color available per sprite), doubling their height or width, flipping their shape to a mirror image, creating motion sequences, and so forth. However, the sprites are only "borrowed" and cannot be integrated into the user's own program unless the same cartridge is on board when the program is run.
Video.
In BASIC mode, the display on the ECS is 20 columns across (while the maximum program line length is 39 characters), and any text is shown in all capital letters. The normal text color is black against a green background. Color codes are used by the ECS to mark different elements of a program as each line is entered or (in immediate mode) executed. The color-coding scheme, which is explained in the back of the manual or can be discerned from direct observation, is useful in determining how the ECS understood (or misunderstood) any command. As to graphics, the background screen is composed of 240 "cards" (20 wide by 12 high, numbered 0 to 239, each composed of 8x8 pixels), in a choice of one of 16 colors (eight primary and eight pastel). Eight sprites at a time may be SHOWn or GRABbed from a storehouse of such images in each individual Intellivision cartridge, and such sprites can then be manipulated by changing their colors (1 color available per sprite), doubling their height or width, flipping their shape to a mirror image, creating motion sequences, and so forth. However, the sprites are only "borrowed" and cannot be integrated into the user's own program unless the same cartridge is on board when the program is run. (Professional programmers found ways to create the illusion of putting more than eight sprites on the Intellivision screen at the same time through multiplexing-- redefining and repositioning a single object from one frame to the next and back again, resulting in flickering images of two objects-- and sequencing graphics RAM to animate background cards.)
Interfacing.
For 600-baud cassette tape recorder access to load and save programs, the ECS has jacks marked OUT TO TAPE, IN FROM TAPE, and REMOTE. While almost any recorder with similar ports can be used, Mattel marketed the Aquarius Data Recorder for use with the ECS, and that unit has the appropriate sockets (labeled MIC, EAR and REM). To attach to the ECS, three straight-through cables are needed, two with mini-plugs on both ends and one with sub-mini-plugs on both ends (for the REMOTE connection). Tape access on the ECS is supported by BASIC keywords for loading (CLOD), saving (CSAV) and verifying (CVRF). The Intellivision hand controllers are pressed to advance through the SET-GO-SAVE/LOAD/VERF sequence. While programs can be saved and accessed without file names, file names up to four characters long (e.g., CSAV PROG) are supported (quote marks are not used around the file names), and the computer will search for the named program to load or verify.
The printer interface, being the AUX jack, is the same as on the Mattel Aquarius: a mini-stereo socket with just 3 lines. The Aquarius printers could be used with the ECS, and came with their own cables. However, the ECS like the Aquarius used standard RS-232C serial signals (+12VDC/-12VDC), so it was possible to interface many RS-232C serial printers. The ECS/Aquarius used a 1200 baud rate, 8 data bits, 2 stop bits, and no parity; the printer needed to be set to these selections with no line feed (sometimes called "carriage return only", "CR", "new line invalid", or "line feed inhibit"), and Busy/Ready instead of X-on/X-off. Typical serial printers had DB-25 interfaces; some had DE-9 interfaces; and, some Radio Shack (RS) printers had round 4-pin female DIN connector serial interfaces (with the pin sockets numbered left-to-right: 4, 3, 2, 1). The proper cable for connecting such a printer is as follows:
 MINI-STEREO PLUG DB-25 DE-9 RS FUNCTION
 Tip/Center of Plug Pin 3 Pin 2 Pin 4 Data to Printer
 Middle of Plug Pin 20 Pin 4 Pin 2 Printer Busy/Ready
 Base/Outside Pin 7 Pin 5 Pin 3 Signal Ground
To access the printer, the command sequence is:
 D=-1
 CALL OUTP
and to cancel the access:
 D=1
 CALL OUTP


Harmonium


European Network for Training and Research in Electrical Engineering

Exchange programs for Electrical Engineering students between 18 universities in Europe. It is also known as "Entree". Their members are:


POST card

In computing, a POST card is a plug-in diagnostic interface card that displays progress and error codes generated during power-on self-test (POST) of a computer. It is used to troubleshoot computers that do not start up.
Working principle.
At a minimum, if the CPU, BIOS, and the I/O interface upon which the POST card relies on are all working, a POST card can be used to monitor the system's Power-On Self Test (POST), or to diagnose problems with it. The system introduced on IBM PC computers sends 8-bit byte codes (usually displayed as two hexadecimal digits) to a specified I/O port (usually 80 hex) during startup, some indicating a stage in the startup procedure, others identifying errors. The description for each code must be looked up in a table for the particular BIOS. For example, for the 1984 IBM PC/AT code 1D is issued when about to "Determine Memory Size Above 1024K", and code 2D in the event of "8042 Keyboard Controller Failure, 105 System Error". If startup does not complete successfully, either an error code, or the code of the last operation performed, is available.
POST cards provide information even when a standard display is not available, either because connecting a monitor is impractical, or because the failure occurs before the video subsystem is operational.
Operation.
POST cards are inserted into an expansion slot, and are available with connectors for the ISA (also supporting EISA), PCI, PCI Express, Mini PCIe (for laptops), Universal Serial Bus, or Low Pin Count bus, or for a parallel port. A typical card for desktop computers has a different bus interface on each edge; a card for laptop computers may have both a miniPCI and a parallel port connector (plus USB to supply power).
Modern motherboards often do not broadcast POST codes to their PCI Express slots (PCIe switches only pass on transactions after having been configured to do so by the BIOS). On such motherboards, the Low Pin Count (LPC) bus, an ISA variant normally used to connect a Trusted Platform Module (TPM), may be the only bus where POST messages can still be seen. However LPC connectors are not standardized, with between 9 and 19 pins and both 2.54 mm and 2 mm pin headers commonly used. Therefore, an LPC POST card may have to auto-detect first the pin assignment used.
Another option are USB POST cards such as AMI Debug Rx, which use the debug port common on USB 2.0 EHCI controllers.
Information on the meaning of POST codes for different BIOSes is needed to interpret the codes. This may be supplied with cards, but becomes dated as later BIOSes are issued; more up-to-date information may be available on manufacturers' and independent websites.
In addition to displaying numeric codes, many cards monitor power supply voltages, clock and oscillator signals, reset signal, and other parameters.
Usage scenarios.
Diagnostic cards are today mainly used by designers of motherboards and extension cards, along with logic analyzers and other debug tools and interfaces. They are less commonly used in the 21st century for computer repair and by system integrators, but remain available. POST cards for PCs, while originally high-priced, cost from just a few US dollars upwards in the 21st century.
Some motherboards have a built-in display to diagnose hardware problems. Most also report POST errors with audible beeps, if a PC speaker is attached. Such motherboards make POST cards less necessary.
When these diagnostic cards were first introduced motherboards were expensive and well worth troubleshooting and repairing. By the late twentieth century large scale integration, mass production made motherboards inexpensive components. Motherboards were rarely repaired, but replaced; the main purpose of a POST card is to determine that parts mounted on the motherboard itself, rather than plugged-in video cards, RAM, etc. are at fault.


Gain (electronics)

In electronics, gain is a measure of the ability of a two-port circuit (often an amplifier) to increase the power or amplitude of a signal from the input to the output port by adding energy converted from some power supply to the signal. It is usually defined as the mean ratio of the signal amplitude or power at the output port to the amplitude or power at the input port. It is often expressed using the logarithmic decibel (dB) units ("dB gain"). A gain greater than one (greater than zero dB), that is amplification, is the defining property of an active component or circuit, while a passive circuit will have a gain of less than one.
The term "gain" alone is ambiguous, and can refer to the ratio of output to input voltage ("voltage gain"), current ("current gain") or electric power ("power gain"). In the field of audio and general purpose amplifiers, especially operational amplifiers, the term usually refers to voltage gain, but in radio frequency amplifiers it usually refers to power gain. Furthermore, the term gain is also applied in systems such as sensors where the input and output have different units; in such cases the gain units must be specified, as in "5 microvolts per photon" for the responsivity of a photosensor. The "gain" of a bipolar transistor normally refers to forward current transfer ratio, either "h"FE ("beta", the static ratio of "I""c" divided by "I"b at some operating point), or sometimes "h"fe (the small-signal current gain, the slope of the graph of "I""c" against "I""b" at a point).
The gain of an electronic device or circuit generally varies with the frequency of the applied signal. Unless otherwise stated, the term refers to the gain for frequencies in the passband, the intended operating frequency range of the equipment.
The term "gain" has a different meaning in antenna design; antenna gain is the ratio of radiation intensity from a directional antenna to formula_1 (mean radiation intensity from a lossless antenna).
Logarithmic units and decibels.
Power gain.
Power gain, in decibels (dB), is defined as follows:
where formula_3 is the power applied to the input, formula_4 is the power from the output.
A similar calculation can be done using a natural logarithm instead of a decimal logarithm, resulting in nepers instead of decibels:
Voltage gain.
The power gain can be calculated using voltage instead of power using Joule's first law formula_6; the formula is:
In many cases, the input impedance formula_8 and output impedance formula_9 are equal, so the above equation can be simplified to:
This simplified formula, the 20 log rule, is used to calculate a voltage gain in decibels and is equivalent to a power gain if and only if the impedances at input and output are equal.
Current gain.
In the same way, when power gain is calculated using current instead of power, making the substitution formula_12, the formula is:
In many cases, the input and output impedances are equal, so the above equation can be simplified to:
This simplified formula is used to calculate a current gain in decibels and is equivalent to the power gain if and only if the impedances at input and output are equal.
The "current gain" of a bipolar transistor, formula_16 or formula_17, is normally given as a dimensionless number, the ratio of formula_18 to formula_19 (or slope of the formula_18-versus-formula_19 graph, for formula_17).
In the cases above, gain will be a dimensionless quantity, as it is the ratio of like units (decibels are not used as units, but rather as a method of indicating a logarithmic relationship). In the bipolar transistor example, it is the ratio of the output current to the input current, both measured in amperes. In the case of other devices, the gain will have a value in SI units. Such is the case with the operational transconductance amplifier, which has an open-loop gain (transconductance) in siemens (mhos), because the gain is a ratio of the output current to the input voltage.
Example.
Q. An amplifier has an input impedance of 50 ohms and drives a load of 50 ohms. When its input (formula_23) is 1 volt, its output (formula_24) is 10 volts. What is its voltage and power gain?
A. Voltage gain is simply:
The units V/V are optional but make it clear that this figure is a voltage gain and not a power gain.
Using the expression for power, "P" = "V"2/"R", the power gain is:
Again, the units W/W are optional. Power gain is more usually expressed in decibels, thus:
A gain of factor 1 (equivalent to 0 dB) where both input and output are at the same voltage level and impedance is also known as "unity gain".


Hoyts Kiosk

Hoyts Kiosk, previously known as Oovie, was an Australian company that specialised in the rental of DVDs and Blu-ray Discs via automated retail kiosks. In 2013, Hoyts Kiosk had over 500 kiosks in Australia, located in every state and territory except South Australia, with more than 250,000 active customers.
History.
Hoyts Kiosk was launched as Instant DVD by Sydney-based entrepreneurs Andrew Evetts and Ian O'Rourke in 2005. They were inspired by seeing the success of similar DVD rental kiosks in the United States. In October 2009 they sold the business to Hoyts who rebranded the company as Oovie.
In November 2017, Hoyts Kiosk was acquired by Video Ezy Express and all its machines were rebranded.
Kiosks.
Kiosks were located at grocery stores, shopping centres, convenience stores, and fast food restaurants. Customers could choose a DVD or Blu-ray disc at any kiosk, or select and reserve online for collection at a kiosk. Discs could be returned to any kiosk in Australia. Movies had to be returned by 9 pm the following day or a further day's rental was charged.


Tetronarce macneilli

Tetronarce macneilli, commonly known as the Shorttail torpedo, is a species of large electric ray. The taxonomy of the species has been long debated and has been suggested that it is synonymous with "Torpedo fairchildi".
Distribution and Habitat.
This species is found off of southern Australia from Port Hedland to the Swain Reefs in tropical-cool temperate waters. It is noted for having an unusually large range for a ray species. It inhabits sloped continental shelves and slopes from to . It feeds on fishes and crustaceans.
Description.
"T. macneilli" can grow up to long. It is capable of delivering an intense electric shock if handled in defense and also uses this ability to hunt prey.


SS City of Chester

The SS "City of Chester" was a steamship built in 1875 that sank after a collision with RMS "Oceanic" at the Golden Gate in San Francisco Bay on August 22, 1888.
"City of Chester" was long. She was owned by the Oregon Railroad Co. and leased by the Pacific Coast Steamship Company.
Sinking.
Heading to Eureka, California, with 90 passengers on the foggy morning of August 22, 1888, at about 10 am she collided with RMS "Oceanic", a liner inbound from Hong Kong. The two ships saw each other, but as was later determined by a British Naval Court, "City of Chester" was caught by tidal current and carried into the path of the larger ship. An eyewitness aboard "Oceanic" said: "Into her we crashed with irrisistible force, cutting her just as though she was a cheese." She sank in six minutes, and despite rescue efforts by those aboard "Oceanic", sixteen passengers, including two children, and three crew members died. In terms of loss of life, this is the second most deadly wreck in the history of San Francisco Bay, after the sinking of the in 1901.
"Oceanic" had Chinese crew and her steerage passengers were Chinese immigrants; anti-Chinese xenophobia was high in the US at the time and initially the Chinese were accused of letting "City of Chester"s passengers drown. When news of their efforts to save them came out, it helped to reduce the prejudice against the Chinese.
Discovery of wreck.
The wreck is located in of water just inside the Golden Gate Bridge at and was found in May 2013 by NOAA Office of Coast Survey Navigational Response Team 6 using multi-beam sonar. It is only from where it was located by a precursor of NOAA, the U.S. Coast and Geodetic Survey, in September 1888 in a geodetic survey using a wire dragged from the tug "Raymond".
An exhibit on "City of Chester" is to be created at the Gulf of the Farallones National Marine Sanctuary office at Crissy Field. The office occupies the building erected as a lifesaving station in response to the disaster.


Institution of Electrical Engineers

The Institution of Electrical Engineers (IEE) was a British professional organisation of electronics, electrical, manufacturing, and Information Technology professionals, especially electrical engineers. It began in 1871 as the Society of Telegraph Engineers. In 2006, it ceased to exist independently, becoming part of the Institution of Engineering and Technology (IET).
Notable past presidents have included Lord Kelvin (1889), Sir Joseph Swan (1898) and Sebastian de Ferranti (1910–11). Notable chairmen include John M. M. Munro (1910–11).
History.
The IEE was founded in 1871 as the Society of Telegraph Engineers, changed its name in 1880 to the Society of Telegraph Engineers and Electricians and changed to the Institution of Electrical Engineers in 1888. It was Incorporated by a Royal Charter in 1921.
In 1988 the Institution of Electrical Engineers (IEE) merged with the Institution of Electronic and Radio Engineers (IERE), originally the British Institution of Radio Engineers (Brit IRE) founded in 1925.
By the mid-2000s, the IEE was the largest professional engineering society in Europe, with a worldwide membership of around 120,000. Discussions about a merger with the Institution of Incorporated Engineers (IIE) about the formation of a new institution started in 2004, and following membership voting, the IEE merged with the IIE on 31 March 2006 to form the Institution of Engineering and Technology (IET).
IEE Global.
IEE has a global presence, through having section offices in different countries around the world. This include Hong Kong. India,
Greece and Malta.


Mixing (mathematics)

In mathematics, mixing is an abstract concept originating from physics: the attempt to describe the irreversible thermodynamic process of mixing in the everyday world: mixing paint, mixing drinks, industrial mixing, "etc".
The concept appears in ergodic theory—the study of stochastic processes and measure-preserving dynamical systems. Several different definitions for mixing exist, including "strong mixing", "weak mixing" and "topological mixing", with the last not requiring a measure to be defined. Some of the different definitions of mixing can be arranged in a hierarchical order; thus, strong mixing implies weak mixing. Furthermore, weak mixing (and thus also strong mixing) implies ergodicity: that is, every system that is weakly mixing is also ergodic (and so one says that mixing is a "stronger" notion than ergodicity).
Informal explanation.
The mathematical definition of mixing aims to capture the ordinary every-day process of mixing, such as mixing paints, drinks, cooking ingredients, industrial process mixing, smoke in a smoke-filled room, and so on. To provide the mathematical rigor, such descriptions begin with the definition of a measure-preserving dynamical system, written as formula_1.
The set formula_2 is understood to be the total space to be filled: the mixing bowl, the smoke-filled room, "etc." The measure formula_3 is understood to define the natural volume of the space formula_2 and of its subspaces. The collection of subspaces is denoted by formula_5, and the size of any given subset formula_6 is formula_7; the size is its volume. Naively, one could imagine formula_5 to be the power set of formula_2; this doesn't quite work, as not all subsets of a space have a volume (famously, the Banach-Tarski paradox). Thus, conventionally, formula_5 consists of the measurable subsets—the subsets that do have a volume. It is always taken to be a Borel set—the collection of subsets that can be constructed by taking intersections, unions and set complements; these can always be taken to be measurable.
The time evolution of the system is described by a map formula_11. Given some subset formula_6, its map formula_13 will in general be a deformed version of formula_14 – it is squashed or stretched, folded or cut into pieces. Mathematical examples include the baker's map and the horseshoe map, both inspired by bread-making. The set formula_13 must have the same volume as formula_14; the squashing/stretching does not alter the volume of the space, only its distribution. Such a system is "measure-preserving" (area-preserving, volume-preserving).
A formal difficulty arises when one tries to reconcile the volume of sets with the need to preserve their size under a map. The problem arises because, in general, several different points in the domain of a function can map to the same point in its range; that is, there may be formula_17 with formula_18. Worse, a single point formula_19 has no size. These difficulties can be avoided by working with the inverse map formula_20; it will map any given subset formula_6 to the parts that were assembled to make it: these parts are formula_22. It has the important property of not "losing track" of where things came from. More strongly, it has the important property that "any" (measure-preserving) map formula_23 is the inverse of some map formula_24. The proper definition of a volume-preserving map is one for which formula_25 because formula_26 describes all the pieces-parts that formula_14 came from.
One is now interested in studying the time evolution of the system. If a set formula_28 eventually visits all of formula_2 over a long period of time (that is, if formula_30 approaches all of formula_2 for large formula_32), the system is said to be ergodic. If every set formula_14 behaves in this way, the system is a conservative system, placed in contrast to a dissipative system, where some subsets formula_14 wander away, never to be returned to. An example would be water running downhill -- once it's run down, it will never come back up again. The lake that forms at the bottom of this river can, however, become well-mixed. The ergodic decomposition theorem states that every ergodic system can be split into two parts: the conservative part, and the dissipative part.
Mixing is a stronger statement than ergodicity. Mixing asks for this ergodic property to hold between any two sets formula_35, and not just between some set formula_14 and formula_2. That is, given any two sets formula_38, a system is said to be (topologically) mixing if there is an integer formula_39 such that, for all formula_40 and formula_41, one has that formula_42. Here, formula_43 denotes set intersection and formula_44 is the empty set.
The above definition of topological mixing should be enough to provide an informal idea of mixing (it is equivalent to the formal definition, given below). However, it made no mention of the volume of formula_14 and formula_46, and, indeed, there is another definition that explicitly works with the volume. Several, actually; one has both strong mixing and weak mixing; they are inequivalent, although a strong mixing system is always weakly mixing. The measure-based definitions are not compatible with the definition of topological mixing: there are systems which are one, but not the other. The general situation remains cloudy: for example, given three sets formula_47, one can define 3-mixing. As of 2020, it is not known if 2-mixing implies 3-mixing. (If one thinks of ergodicity as "1-mixing", then it is clear that 1-mixing does not imply 2-mixing; there are systems that are ergodic but not mixing.)
The concept of "strong mixing" is made in reference to the volume of a pair of sets. Consider, for example, a set formula_14 of colored dye that is being mixed into a cup of some sort of sticky liquid, say, corn syrup, or shampoo, or the like. Practical experience shows that mixing sticky fluids can be quite hard: there is usually some corner of the container where it is hard to get the dye mixed into. Pick as set formula_46 that hard-to-reach corner. The question of mixing is then, can formula_14, after a long enough period of time, not only penetrate into formula_46 but also fill formula_46 with the same proportion as it does elsewhere?
One phrases the definition of strong mixing as the requirement that
The time parameter formula_32 serves to separate formula_14 and formula_46 in time, so that one is mixing formula_14 while holding the test volume formula_46 fixed. The product formula_59 is a bit more subtle. Imagine that the volume formula_46 is 10% of the total volume, and that the volume of dye formula_14 will also be 10% of the grand total. If formula_14 is uniformly distributed, then it is occupying 10% of formula_46, which itself is 10% of the total, and so, in the end, after mixing, the part of formula_14 that is in formula_46 is 1% of the total volume. That is, formula_66 This product-of-volumes has more than passing resemblance to Bayes theorem in probabilities; this is not an accident, but rather a consequence that measure theory and probability theory are the same theory: they share the same axioms (the Kolmogorov axioms), even as they use different notation.
The reason for using formula_67 instead of formula_68 in the definition is a bit subtle, but it follows from the same reasons why
formula_69 was used to define the concept of a measure-preserving map. When looking at how much dye got mixed into the corner formula_46, one wants to look at where that dye "came from" (presumably, it was poured in at the top, at some time in the past). One must be sure that every place it might have "come from" eventually gets mixed into formula_46.
Mixing in dynamical systems.
Let formula_1 be a measure-preserving dynamical system, with "T" being the time-evolution or shift operator. The system is said to be strong mixing if, for any formula_73, one has
For shifts parametrized by a continuous variable instead of a discrete integer "n", the same definition applies, with formula_75 replaced by formula_76 with "g" being the continuous-time parameter.
A dynamical system is said to be weak mixing if one has
In other words, formula_78 is strong mixing if formula_79 in the usual sense, weak mixing if
in the Cesàro sense, and ergodic if formula_81 in the Cesàro sense. Hence, strong mixing implies weak mixing, which implies ergodicity. However, the converse is not true: there exist ergodic dynamical systems which are not weakly mixing, and weakly mixing dynamical systems which are not strongly mixing. The Chacon system was historically the first example given of a system that is weak-mixing but not strong-mixing.
formula_82 formulation.
The properties of ergodicity, weak mixing and strong mixing of a measure-preserving dynamical system can also be characterized by the average of observables. By von Neumann's ergodic theorem, ergodicity of a dynamical system formula_1 is equivalent to the property that, for any function formula_84, the sequence formula_85 converges strongly and in the sense of Cesàro to formula_86, i.e.,
A dynamical system formula_1 is weakly mixing if, for any functions formula_89 and formula_90
A dynamical system formula_1 is strongly mixing if, for any function formula_93 the sequence formula_85 converges weakly to formula_95 i.e., for any function formula_90
Since the system is assumed to be measure preserving, this last line is equivalent to saying that the covariance formula_98 so that the random variables formula_99 and formula_100 become orthogonal as formula_32 grows. Actually, since this works for any function formula_102 one can informally see mixing as the property that the random variables formula_99 and formula_100 become independent as formula_32 grows.
Products of dynamical systems.
Given two measured dynamical systems formula_106 and formula_107 one can construct a dynamical system formula_108 on the Cartesian product by defining formula_109 We then have the following characterizations of weak mixing:
Generalizations.
The definition given above is sometimes called strong 2-mixing, to distinguish it from higher orders of mixing. A strong 3-mixing system may be defined as a system for which
holds for all measurable sets "A", "B", "C". We can define strong k-mixing similarly. A system which is strong "k"-mixing for all "k" = 2,3,4... is called mixing of all orders.
It is unknown whether strong 2-mixing implies strong 3-mixing. It is known that strong "m"-mixing implies ergodicity.
Examples.
Irrational rotations of the circle, and more generally irreducible translations on a torus, are ergodic but neither strongly nor weakly mixing with respect to the Lebesgue measure.
Many maps considered as chaotic are strongly mixing for some well-chosen invariant measure, including: the dyadic map, Arnold's cat map, horseshoe maps, Kolmogorov automorphisms, and the Anosov flow (the geodesic flow on the unit tangent bundle of compact manifolds of negative curvature.)
Topological mixing.
A form of mixing may be defined without appeal to a measure, using only the topology of the system. A continuous map formula_117 is said to be topologically transitive if, for every pair of non-empty open sets formula_118, there exists an integer "n" such that
where formula_120 is the "n"th iterate of "f". In the operator theory, a topologically transitive bounded linear operator (a continuous linear map on a topological vector space) is usually called hypercyclic operator. A related idea is expressed by the wandering set.
Lemma: If "X" is a complete metric space with no isolated point, then "f" is topologically transitive if and only if there exists a hypercyclic point formula_19, that is, a point "x" such that its orbit formula_122 is dense in "X".
A system is said to be topologically mixing if, given open sets formula_14 and formula_46, there exists an integer "N", such that, for all formula_41, one has
For a continuous-time system, formula_120 is replaced by the flow formula_128, with "g" being the continuous parameter, with the requirement that a non-empty intersection hold for all formula_129.
A weak topological mixing is one that has no non-constant continuous (with respect to the topology) eigenfunctions of the shift operator.
Topological mixing neither implies, nor is implied by either weak or strong mixing: there are examples of systems that are weak mixing but not topologically mixing, and examples that are topologically mixing but not strong mixing.
Mixing in stochastic processes.
Let formula_130 be a stochastic process on a probability space formula_131. The sequence space into which the process maps can be endowed with a topology, the product topology. The open sets of this topology are called cylinder sets. These cylinder sets generate a σ-algebra, the Borel σ-algebra; this is the smallest σ-algebra that contains the topology.
Define a function formula_132, called the strong mixing coefficient, as
for all formula_134. The symbol formula_135, with formula_136 denotes a sub-σ-algebra of the σ-algebra; it is the set of cylinder sets that are specified between times "a" and "b", i.e. the σ-algebra generated by formula_137.
The process formula_130 is said to be strongly mixing if formula_139 as formula_140. That is to say, a strongly mixing process is such that, in a way that is uniform over all times formula_141 and all events, the events before time formula_141 and the events after time formula_143 tend towards being independent as formula_144; more colloquially, the process, in a strong sense, forgets its history.
Mixing in Markov processes.
Suppose formula_145 were a stationary Markov process with stationary distribution formula_146 and let formula_147 denote the space of Borel-measurable functions that are square-integrable with respect to the measure formula_146. Also let
denote the conditional expectation operator on formula_150 Finally, let
denote the space of square-integrable functions with mean zero.
The "ρ"-mixing coefficients of the process {"xt"} are
The process is called "ρ"-mixing if these coefficients converge to zero as , and “"ρ"-mixing with exponential decay rate” if for some . For a stationary Markov process, the coefficients "ρt" may either decay at an exponential rate, or be always equal to one.
The "α"-mixing coefficients of the process {"xt"} are
The process is called "α"-mixing if these coefficients converge to zero as , it is “α-mixing with exponential decay rate” if for some , and it is α-mixing with a sub-exponential decay rate if for some non-increasing function formula_154 satisfying
as formula_156.
The "α"-mixing coefficients are always smaller than the "ρ"-mixing ones: , therefore if the process is "ρ"-mixing, it will necessarily be "α"-mixing too. However, when , the process may still be "α"-mixing, with sub-exponential decay rate.
The "β"-mixing coefficients are given by
The process is called "β"-mixing if these coefficients converge to zero as , it is β-mixing with an exponential decay rate if for some , and it is β-mixing with a sub-exponential decay rate if as for some non-increasing function formula_154 satisfying
as formula_156.
A strictly stationary Markov process is "β"-mixing if and only if it is an aperiodic recurrent Harris chain. The "β"-mixing coefficients are always bigger than the "α"-mixing ones, so if a process is "β"-mixing it will also be "α"-mixing. There is no direct relationship between "β"-mixing and "ρ"-mixing: neither of them implies the other.