CHERNOBYL, THE WORST NUCLEAR DISASTER IN HISTORY

On a day like today in 1986, the Chernobyl disaster occurred. It is considered the worst nuclear in our history and today, years and years later, the effects of this terrible tragedy are still visible.

The citizens of Pripyat and the members of the emergency services who were the first to arrive to the central to try to avoid more tragic consequences were the most affected. The most part of them died or suffered (and suffer) the sequels of this terrible accident.

The Grandma wants to talk about this incident, and she wants to think about the real necessity of having nuclear plants when we are a planet rich in natural sources and green energies.

The Chernobyl disaster was a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR in the Soviet Union.

It is considered the worst nuclear disaster in history both in terms of cost and casualties, and is one of only two nuclear energy accidents rated at seven -the maximum severity- on the International Nuclear Event Scale, the other being the 2011 Fukushima Daiichi nuclear disaster in Japan.

The initial emergency response, together with later decontamination of the environment, ultimately involved more than 500,000 personnel and cost an estimated 18 billion Soviet rubles -roughly US$68 billion in 2019, adjusted for inflation.

The accident started during a safety test on an RBMK-type nuclear reactor. The test was a simulation of an electrical power outage to help create a safety procedure for maintaining reactor cooling water circulation until the back-up electrical generators could provide power. Three such tests had been conducted since 1982, but they had failed to provide a solution. On this fourth attempt, an unexpected 10-hour delay meant that an unprepared operating shift was on duty.

More information: Chornobyl NPP

During the planned decrease of reactor power in preparation for the electrical test, the power unexpectedly dropped to a near-zero level.

The operators were able to only partially restore the specified test power, which put the reactor in an unstable condition. This risk was not made evident in the operating instructions, so the operators proceeded with the electrical test. Upon test completion, the operators triggered a reactor shutdown, but a combination of unstable conditions and reactor design flaws caused an uncontrolled nuclear chain reaction instead.

A large amount of energy was suddenly released, and two explosions ruptured the reactor core and destroyed the reactor building.

One was a highly destructive steam explosion from the vaporizing superheated cooling water; the other explosion could have been another steam explosion or a small nuclear explosion, akin to a nuclear fizzle. This was immediately followed by an open-air reactor core fire that released considerable airborne radioactive contamination for about nine days that precipitated onto parts of the USSR and Western Europe, especially Belarus, 16 km away, where around 70% landed, before being finally contained on 4 May 1986.

The fire gradually released about the same amount of contamination as the initial explosion. As a result of rising ambient radiation levels off-site, a 10-kilometre radius exclusion zone was created 36 hours after the accident. About 49,000 people were evacuated from the area, primarily from Pripyat. The exclusion zone was later increased to 30 kilometres when a further 68,000 people were evacuated from the wider area.

More information: World Nuclear Association

The reactor explosion killed two of the reactor operating staff. A massive emergency operation to put out the fire, stabilize the reactor, and clean-up the ejected nuclear core began. In the disaster and immediate response, 134 station staff and firemen were hospitalized with acute radiation syndrome due to absorbing high doses of ionizing radiation. Of these 134 people, 28 died in the days of months afterward and approximately 14 suspected radiation-induced cancer deaths followed within the next 10 years. Significant clean-up operations were taken in the exclusion zone to deal with local fallout, and the exclusion zone was made permanent.

Among the wider population, an excess of 15 childhood thyroid cancer deaths were documented as of 2011. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has, at multiple times, reviewed all the published research on the incident and found that at present, fewer than 100 documented deaths are likely to be attributable to increased exposure to radiation.

Determining the total eventual number of exposure related deaths is uncertain based on the linear no-threshold model, a contested statistical model, which has also been used in estimates of low level radon and air pollution exposure. Model predictions with the greatest confidence values of the eventual total death toll in the decades ahead from Chernobyl releases vary, from 4,000 fatalities when solely assessing the three most contaminated former Soviet states, to about 9,000 to 16,000 fatalities when assessing the total continent of Europe. 

To reduce the spread of radioactive contamination from the wreckage and protect it from weathering, the protective Chernobyl Nuclear Power Plant sarcophagus was built by December 1986.

It also provided radiological protection for the crews of the undamaged reactors at the site, which continued operating.

Due to the continued deterioration of the sarcophagus, it was further enclosed in 2017 by the Chernobyl New Safe Confinement, a larger enclosure that allows the removal of both the sarcophagus and the reactor debris, while containing the radioactive hazard. Nuclear clean-up is scheduled for completion in 2065.

The ionizing radiation levels in the worst-hit areas of the reactor building have been estimated to be 5.6 roentgens per second (R/s), equivalent to more than 20,000 roentgens per hour. A lethal dose is around 500 roentgens (~5 Gray (Gy) in modern radiation units) over five hours, so in some areas, unprotected workers received fatal doses in less than a minute. However, a dosimeter capable of measuring up to 1,000 R/s was buried in the rubble of a collapsed part of the building, and another one failed when turned on. All remaining dosimeters had limits of 0.001 R/s and therefore read off scale. Thus, the reactor crew could ascertain only that the radiation levels were somewhere above 0.001 R/s, while the true levels were much higher in some areas.

Because of the inaccurate low readings, the reactor crew chief Aleksandr Akimov assumed that the reactor was intact. The evidence of pieces of graphite and reactor fuel lying around the building was ignored, and the readings of another dosimeter brought in by 04:30 were dismissed under the assumption that the new dosimeter must have been defective. Akimov stayed with his crew in the reactor building until morning, sending members of his crew to try to pump water into the reactor. None of them wore any protective gear. Most, including Akimov, died from radiation exposure within three weeks.

More information: BBC

The nearby city of Pripyat was not immediately evacuated. The townspeople, in the early hours of the morning, at 01:23 local time, went about their usual business, completely oblivious to what had just happened. However, within a few hours of the explosion, dozens of people fell ill. Later, they reported severe headaches and metallic tastes in their mouths, along with uncontrollable fits of coughing and vomiting. As the plant was run by authorities in Moscow, the government of Ukraine did not receive prompt information on the accident.

To expedite the evacuation, residents were told to bring only what was necessary, and that they would remain evacuated for approximately three days. As a result, most personal belongings were left behind, and remain there today.

By 15:00, 53,000 people were evacuated to various villages of the Kiev region. The next day, talks began for evacuating people from the 10-kilometre zone. Ten days after the accident, the evacuation area was expanded to 30 kilometres.

The Chernobyl Nuclear Power Plant Exclusion Zone has remained ever since, although its shape has changed and its size has been expanded.

 More information: United States Nuclear Regulatory Commission

The surveying and detection of isolated fallout hotspots outside this zone over the following year eventually resulted in 135,000 long-term evacuees in total agreeing to be moved.

The years between 1986 and 2000 saw the near tripling in the total number of permanently resettled persons from the most severely contaminated areas to approximately 350,000.

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions, much of it deposited on mountainous regions such as the Alps, the Welsh mountains and the Scottish Highlands, where adiabatic cooling caused radioactive rainfall.

The resulting patches of contamination were often highly localized, and localized water-flows contributed to large variations in radioactivity over small areas.

Sweden and Norway also received heavy fallout when the contaminated air collided with a cold front, bringing rain. There was also groundwater contamination.

More information: National Geographic

Chernobyl is a unique place on the planet,
where nature revives after a world-wide man-made disaster,
where there is a real 'ghost town.'

Volodymyr Zelensky

1991, THE WARSAW PACT IS DISBANDED IN BUDAPEST

Today, The Grandma is relaxing at home. She has been reading about the Warsaw Treaty Organization, the defence treaty signed in Warsaw (Poland) in May 1955 during the Cold War. The Warsaw Treaty was disbanded in Budapest on a day like today in 1991.

The Warsaw Treaty Organization (WTO), officially the Treaty of Friendship, Cooperation and Mutual Assistance, commonly known as the Warsaw Pact (WP), was a collective defence treaty signed in Warsaw, Poland between the Soviet Union and seven other Eastern Bloc socialist republics of Central and Eastern Europe in May 1955, during the Cold War.

The Warsaw Pact was the military complement to the Council for Mutual Economic Assistance (CoMEcon), the regional economic organization for the socialist states of Central and Eastern Europe.

The Warsaw Pact was created in reaction to the integration of West Germany into NATO in 1955 per the London and Paris Conferences of 1954, but it is also considered to have been motivated by Soviet desires to maintain control over military forces in Central and Eastern Europe.

The Warsaw Pact was established as a balance of power or counterweight to NATO.

There was no direct military confrontation between them; instead, the conflict was fought on an ideological basis and in proxy wars. Both NATO and the Warsaw Pact led to the expansion of military forces and their integration into the respective blocs. Its largest military engagement was the Warsaw Pact invasion of Czechoslovakia in August 1968 with the participation of all Pact nations except Albania and Romania, which, in part, resulted in Albania withdrawing from the Pact less than a month later.

More information: Open Democracy

The Pact began to unravel in its entirety with the spread of the Revolutions of 1989 through the Eastern Bloc, beginning with the Solidarity movement in Poland, its electoral success in June 1989 and the Pan-European Picnic in August 1989.

East Germany withdrew from the Pact following German reunification in 1990.

On 25 February 1991, at a meeting in Hungary, the Pact was declared at an end by the defence and foreign ministers of the six remaining member states.

The USSR itself was dissolved in December 1991, although most of the former Soviet republics formed the Collective Security Treaty Organization shortly thereafter. Throughout the following 20 years, the seven Warsaw Pact countries outside the USSR each joined NATO (East Germany through its reunification with West Germany; and the Czech Republic and Slovakia as separate countries), as did the Baltic States which had been part of the Soviet Union.

The Warsaw Treaty's organization was two-fold: the Political Consultative Committee handled political matters, and the Combined Command of Pact Armed Forces controlled the assigned multi-national forces, with headquarters in Warsaw, Poland.

The Supreme Commander of the Unified Armed Forces of the Warsaw Treaty Organization, which commanded and controlled all the military forces of the member countries, was also a First Deputy Minister of Defence of the USSR, and the Chief of Combined Staff of the Unified Armed Forces of the Warsaw Treaty Organization was also a First Deputy Chief of the General Staff of the Soviet Armed Forces. 

Therefore, although ostensibly an international collective security alliance, the USSR dominated the Warsaw Treaty armed forces, analogous to the United States' domination of the NATO alliance.

The strategy behind the formation of the Warsaw Pact was driven by the desire of the Soviet Union to prevent Central and Eastern Europe being used as a base for its enemies. Its policy was also driven by ideological and geostrategic reasons. Ideologically, the Soviet Union arrogated the right to define socialism and communism and act as the leader of the global socialist movement. A corollary to this was the necessity of intervention if a country appeared to be violating core socialist ideas, explicitly stated in the Brezhnev Doctrine.

Before the creation of the Warsaw Pact, the Czechoslovak leadership, fearful of a rearmed Germany, sought to create a security pact with East Germany and Poland. These states protested strongly against the re-militarization of West Germany.

The Warsaw Pact was put in place as a consequence of the rearming of West Germany inside NATO. Soviet leaders, like many European countries on both sides of the Iron Curtain, feared Germany being once again a military power and a direct threat. The consequences of German militarism remained a fresh memory among the Soviets and Eastern Europeans. As the Soviet Union already had bilateral treaties with all of its eastern satellites, the Pact has been long considered superfluous, and because of the rushed way in which it was conceived, NATO officials labelled it as a cardboard castle.

The USSR, fearing the restoration of German militarism in West Germany, had suggested in 1954 that it join NATO, but this was rejected by the US and UK.

The eight-member countries of the Warsaw Pact pledged the mutual defence of any member who would be attacked. Relations among the treaty signatories were based upon mutual non-intervention in the internal affairs of the member countries, respect for national sovereignty, and political independence.

More information: Thought

For 36 years, NATO and the Warsaw Pact never directly waged war against each other in Europe; the United States and the Soviet Union and their respective allies implemented strategic policies aimed at the containment of each other in Europe, while working and fighting for influence within the wider Cold War on the international stage. These included the Korean War, Vietnam War, Bay of Pigs invasion, Dirty War, Cambodian–Vietnamese War, and others.

In 1989, popular civil and political public discontent toppled the Communist governments of the Warsaw Treaty countries. The beginning of the end of the Warsaw Pact, regardless of military power, was the Pan-European Picnic in August 1989. The event, which goes back to an idea by Otto von Habsburg, caused the mass exodus of GDR citizens and the media-informed population of Eastern Europe felt the loss of power of their rulers and the Iron Curtain broke down completely. This broke the brackets of Eastern Europe, which could no longer be held together militarily by the Warsaw Pact.

Independent national politics made feasible with the perestroika and glasnost policies induced institutional collapse of the Communist government in the USSR in 1991.

From 1989 to 1991, Communist governments were overthrown in Albania, Poland, Hungary, Czechoslovakia, East Germany, Romania, Bulgaria, Yugoslavia, and the Soviet Union.

On 25 February 1991, the Warsaw Pact was declared disbanded at a meeting of defence and foreign ministers from remaining Pact countries meeting in Hungary.

More information: Russia Matters

On the day I became Soviet leader, in March 1985,
I had a special meeting with the leaders
of the Warsaw Pact countries and told them:
You are independent, and we are independent.
You are responsible for your policies,
we are responsible for ours.
We will not intervene in your affairs, I promise you.

Mikhail Gorbachev

THE SOVIET UNION LAUNCHES ITS MIR SPACECRAFT

Mir

Today, The Grandma has returned from Brussels to Barcelona by plane. It has been a short visit to the Belgian and European capital but intensive and amazing one. Brussels is a wonderful place that you must visit with enough time and The Grandma has decided to return very soon accompanied by her closest friends.

During the short flight, The Grandma has been reading about the Mir, the space station launched by the Soviets on a day like today in 1986 The station remained in orbit for 15 years and was occupied for ten of those years.

Mir was a space station that operated in low Earth orbit from 1986 to 2001, operated by the Soviet Union and later by Russia.

Mir was the first modular space station and was assembled in orbit from 1986 to 1996. It had a greater mass than any previous spacecraft.

At the time it was the largest artificial satellite in orbit, succeeded by the International Space Station (ISS) after Mir's orbit decayed. The station served as a microgravity research laboratory in which crews conducted experiments in biology, human biology, physics, astronomy, meteorology, and spacecraft systems with a goal of developing technologies required for permanent occupation of space.

More information: Russian Space Web

Mir was the first continuously inhabited long-term research station in orbit and held the record for the longest continuous human presence in space at 3,644 days, until it was surpassed by the ISS on 23 October 2010. It holds the record for the longest single human spaceflight, with Valeri Polyakov spending 437 days and 18 hours on the station between 1994 and 1995.

Mir was occupied for a total of twelve and a half years out of its fifteen-year lifespan, having the capacity to support a resident crew of three, or larger crews for short visits.

Following the success of the Salyut programme, Mir represented the next stage in the Soviet Union's space station programme. The first module of the station, known as the core module or base block, was launched in 1986 and followed by six further modules.

Mir

Proton rockets were used to launch all of its components except for the docking module, which was installed by US Space Shuttle mission STS-74 in 1995. When complete, the station consisted of seven pressurised modules and several unpressurised components.

Power was provided by several photovoltaic arrays attached directly to the modules. The station was maintained at an orbit between 296 km and 421 km altitude and travelled at an average speed of 27,700 km/h, completing 15.7 orbits per day.

The station was launched as part of the Soviet Union's manned spaceflight programme effort to maintain a long-term research outpost in space, and following the collapse of the USSR, was operated by the new Russian Federal Space Agency (RKA).

As a result, most of the station's occupants were Soviet; through international collaborations such as the Intercosmos, Euromir and Shuttle–Mir programmes, the station was made accessible to space travellers from several Asian, European and North American nations.

 More information: NASA

Mir was deorbited in March 2001 after funding was cut off. The cost of the Mir programme was estimated by former RKA General Director Yuri Koptev in 2001 as $4.2 billion over its lifetime including development, assembly and orbital operation.

Mir was authorised by a 17 February 1976 decree, to design an improved model of the Salyut DOS-17K space stations. Four Salyut space stations had been launched since 1971, with three more being launched during Mir's development.

It was planned that the station's core module (DOS-7 and the backup DOS-8) would be equipped with a total of four docking ports; two at either end of the station as with the Salyut stations, and an additional two ports on either side of a docking sphere at the front of the station to enable further modules to expand the station's capabilities.

More information: The Conversation

By August 1978, this had evolved to the final configuration of one aft port and five ports in a spherical compartment at the forward end of the station.

It was originally planned that the ports would connect to 7.5-tonne modules derived from the Soyuz spacecraft. These modules would have used a Soyuz propulsion module, as in Soyuz and Progress, and the descent and orbital modules would have been replaced with a long laboratory module.

Mir

Following a February 1979 governmental resolution, the programme was consolidated with Vladimir Chelomei's manned Almaz military space station programme. 

The docking ports were reinforced to accommodate 20-tonne space station modules based on the TKS spacecraft. NPO Energia was responsible for the overall space station, with work subcontracted to KB Salyut, due to ongoing work on the Energia rocket and Salyut 7, Soyuz-T, and Progress spacecraft. KB Salyut began work in 1979, and drawings were released in 1982 and 1983.

New systems incorporated into the station included the Salyut 5B digital flight control computer and gyrodyne flywheels, taken from Almaz, Kurs automatic rendezvous system, Luch satellite communications system, Elektron oxygen generators, and Vozdukh carbon dioxide scrubbers.

By early 1984, work on Mir had halted while all resources were being put into the Buran programme in order to prepare the Buran spacecraft for flight testing. Funding resumed in early 1984 when Valentin Glushko was ordered by the Central Committee's Secretary for Space and Defence to orbit Mir by early 1986, in time for the 27th Communist Party Congress.

More information: Universe Today

It was clear that the planned processing flow could not be followed and still meet the 1986 launch date. It was decided on Cosmonaut's Day (12 April) 1985 to ship the flight model of the base block to the Baikonur cosmodrome and conduct the systems testing and integration there.

The module arrived at the launch site on 6 May, with 1100 of 2500 cables requiring rework based on the results of tests to the ground test model at Khrunichev. In October, the base block was rolled outside its cleanroom to carry out communications tests. The first launch attempt on 16 February 1986 was scrubbed when the spacecraft communications failed, but the second launch attempt, on 19 February 1986 at 21:28:23 UTC, was successful, meeting the political deadline.

More information: Seeker

The orbital assembly of Mir began on 19 February 1986 with the launch of the Proton-K rocket. Four of the six modules which were later added (Kvant-2 in 1989, Kristall in 1990, Spektr in 1995 and Priroda in 1996) followed the same sequence to be added to the main Mir complex.

Firstly, the module would be launched independently on its own Proton-K and chase the station automatically. It would then dock to the forward docking port on the core module's docking node, then extend its Lyappa arm to mate with a fixture on the node's exterior. The arm would then lift the module away from the forward docking port and rotate it on to the radial port where it was to mate, before lowering it to dock. The node was equipped with only two Konus drogues, which were required for dockings. This meant that, prior to the arrival of each new module, the node would have to be depressurised to allow spacewalking cosmonauts to manually relocate the drogue to the next port to be occupied.

Mir

The other two expansion modules, Kvant-1 in 1987 and the docking module in 1995, followed different procedures. Kvant-1, having, unlike the four modules mentioned above, no engines of its own, was launched attached to a tug based on the TKS spacecraft which delivered the module to the aft end of the core module instead of the docking node. Once hard docking had been achieved, the tug undocked and deorbited itself.

The docking module, meanwhile, was launched aboard Space Shuttle Atlantis during STS-74 and mated to the orbiter's Orbiter Docking System. Atlantis then docked, via the module, to Kristall, then left the module behind when it undocked later in the mission. Various other external components, including three truss structures, several experiments and other unpressurised elements were also mounted to the exterior of the station by cosmonauts conducting a total of eighty spacewalks over the course of the station's history.

The station's assembly marked the beginning of the third generation of space station design, being the first to consist of more than one primary spacecraft, thus opening a new era in space architecture. First generation stations such as Salyut 1 and Skylab had monolithic designs, consisting of one module with no resupply capability; the second generation stations Salyut 6 and Salyut 7 comprised a monolithic station with two ports to allow consumables to be replenished by cargo spacecraft such as Progress.

The capability of Mir to be expanded with add-on modules meant that each could be designed with a specific purpose in mind -for instance, the core module functioned largely as living quarters-, thus eliminating the need to install all the station's equipment in one module.

The most significant adverse effects of long-term weightlessness are muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. Other significant effects include fluid redistribution, a slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, excess flatulence, and puffiness of the face. These effects begin to reverse quickly upon return to the Earth. 

More information: Astronautix

To prevent some of these effects, the station was equipped with two treadmills in the core module and Kvant-2 and a stationary bicycle in the core module; each cosmonaut was to cycle the equivalent of 10 kilometres and run the equivalent of 5 kilometres per day. Cosmonauts used bungee cords to strap themselves to the treadmill. Researchers believe that exercise is a good countermeasure for the bone and muscle density loss that occurs in low-gravity situations.

The EO-10 crew, launched aboard Soyuz TM-13 on 2 October 1991, was the last crew to launch from the USSR and continued the occupation of Mir during the fall of the Soviet Union. The crew launched as Soviet citizens and returned to Earth on 25 March 1992 as Russians. The newly formed Russian Federal Space Agency (Roskosmos) was unable to finance the unlaunched Spektr and Priroda modules, instead putting them into storage and ending Mir's second expansion.

More information: Popular Mechanics

Following the 8 June 1998 departure of Discovery, the EO-25 crew of Budarin and Musabayev remained on Mir, completing materials experiments and compiling a station inventory. On 2 July, Roskosmos director Yuri Koptev announced that, due to a lack of funding to keep Mir active, the station would be deorbited in June 1999.

The EO-26 crew of Gennady Padalka and Sergei Avdeyev arrived on 15 August in Soyuz TM-28, alongside physicist Yuri Baturin, who departed with the EO-25 crew on 25 August in Soyuz TM-27. The crew carried out two spacewalks, one inside Spektr to reseat some power cables and another outside to set up experiments delivered by Progress M-40, which also carried a large amount of propellant to begin alterations to Mir's orbit in preparation for the station's decommissioning.

More information: ABC News

When you talk to crews that went to Mir

or have gone up to International Space Station,

they say that you go through different phases

of adaptation or getting used to the space environment.

Laurel Clark

TETRIS, THE GAME DESIGNED IN THE SOVIET UNION

Claire Fontaine is playing Tetris at home

Today, The Grandma has gone to visit Claire Fontaine who is totally in love with her new Tetris Machine.

The Grandma has wanted to play a little with Claire's new acquisition and they have spent a wonderful day playing Tetris again and again without stopping.

Tetris, in Russian Тетрис, is a tile-matching puzzle video game originally designed and programmed by Soviet Russian game designer Alexey Leonidovich Pajitnov, in Russian Алексе́й Леони́дович Па́житнов. The first playable version was completed on June 6, 1984, while he was working for the Dorodnitsyn Computing Centre of the Academy of Science of the Soviet Union in Moscow.

He derived its name from the Greek numerical prefix tetra-, all of the game's pieces contain four segments and tennis, Pajitnov's favorite sport. The name is also used in-game to refer to the play where four lines, the maximum simultaneous clearance number, are cleared at once.

Tetris was the first entertainment software to be exported from the Soviet Union to the United States, where it was published by Spectrum HoloByte for the Commodore 64 and IBM PC. The game is a popular use of tetrominoes, the four-element case of polyominoes, which have been used in popular puzzles since at least 1907. The name for these figures was given by the mathematician Solomon W. Golomb in 1953.

Tetris by Alexey Leonidovich Pajitnov

The game, or one of its many variants, is available for nearly every video game console and computer operating system, as well as on devices such as graphing calculators, mobile phones, portable media players, PDAs, Network music players, and as an Easter egg on non-media products like oscilloscopes. It has inspired Tetris serving dishes, and it has even been played on the sides of various buildings.

While versions of Tetris were sold for a range of 1980s home computer platforms as well as arcades, it was the successful handheld version for the Game Boy, launched in 1989, that established the game as one of the most popular video games ever. Electronic Gaming Monthly's 100th issue had Tetris in first place as Greatest Game of All Time.

Tetriminos are game pieces shaped like tetrominoes, geometric shapes composed of four square blocks each. A random sequence of Tetriminos fall down the playing field, a rectangular vertical shaft, called the well or matrix. 

The objective of the game is to manipulate these Tetriminos, by moving each one sideways and/or rotating by quarter-turns, so that they form a solid horizontal line without gaps. When such a line is formed, it disappears and any blocks above it fall down to fill the space. When a certain number of lines are cleared, the game enters a new level. As the game progresses, each level causes the Tetriminos to fall faster, and the game ends when the stack of Tetriminos reaches the top of the playing field and no new Tetriminos are able to enter. Some games also end after a finite number of levels or lines.

More information: Tetris

All of the Tetriminos can fill and clear both singles and doubles. I, J, and L are able to clear triples. Only the I Tetrimino has the capacity to clear four lines simultaneously, and this is referred to as a tetris. This may vary depending on the rotation and compensation rules of each specific Tetris implementation. For instance, in the Super Rotation System used in most recent implementations, certain situations allow T, S, and Z to 'snap' into tight spots and clear triples.

Alexey Leonidovich Pajitnov

Pajitnov's original version for the Electronika 60 computer used green brackets to represent blocks. Versions of Tetris on the original Game Boy/Game Boy Color and on most dedicated handheld games use monochrome or grayscale graphics, but most popular versions use a separate color for each distinct shape.

Prior to The Tetris Company's standardization in the early 2000s, those colors varied widely from implementation to implementation.

The scoring formula for the majority of Tetris products is built on the idea that more difficult line clears should be awarded more points. For example, a single line clear in Tetris Zone is worth 100 points, clearing four lines at once, known as a Tetris, is worth 800, while each subsequent back-to-back Tetris is worth 1,200.

In conjunction, players can be awarded combos that exist in certain games which reward multiple line clears in quick succession. The exact conditions for triggering combos, and the amount of importance assigned to them, vary from game to game.

More information: Live Science

Tetris was created in June 1984 by Alexey Pajitnov, an artificial intelligence researcher working for the Soviet Academy of Sciences at Computer Center in Moscow.

Tasked with testing the capabilities of new hardware, Pajitnov would do so by writing simple games for them. He initially considered creating a game around pentominoes, which featured in puzzle games that he had enjoyed as a child, but felt that it might have been too complicated with twelve different shape variations, so the concept switched to tetrominoes, of which there are seven variants.

The Electronika 60 on which he was working had only a text-based display, so the tetrominoes were formed of letter characters. Realizing that completed lines resulted in the screen filling up quickly, Pajitnov decided to delete them, creating a key part of Tetris gameplay.

Tetris by Alexey Leonidovich Pajitnov

Pajitnov's game proved popular with his colleagues. Academy of Sciences co-workers Dmitry Pavlovsky and Vadim Gerasimov ported the game to the IBM PC.

Gerasimov reports that Pajitnov chose the name Tetris as a combination of tetromino and tennis. From there, the PC game became popular and began spreading around Moscow. Gerasimov removed his 1988 version of the game from his website in October 2003, in response to a demand from counsel for The Tetris Company. He resumed making it available in August 2006.

The PC version made its way to Budapest, Hungary, where it was ported to various platforms and was discovered by British software house Andromeda. They attempted to contact Pajitnov to secure the rights for the PC version, but before the deal was firmly settled, they had already sold the rights to Spectrum HoloByte. After failing to settle the deal with Pajitnov, Andromeda attempted to license it from the Hungarian programmers instead.

Meanwhile, before any legal rights were settled, the Spectrum HoloByte IBM PC version of Tetris, which contained background graphics featuring Russian scenes, was released in the United States in 1987. The game's popularity was tremendous; Computer Gaming World called the game deceptively simple and insidiously addictive.

More information: Den of Geek

The details of the licensing issues were uncertain by this point, but in 1987 Andromeda managed to obtain copyright licensing for the IBM PC and any other home computer system. Their Commodore 64 release in 1988 has a 26-minute soundtrack composed by game musician Wally Beben.

In 1996, the rights to the game reverted from the Russian state to Pajitnov himself, who previously had made very little money from the game. That year, The Tetris Company was founded, claiming to hold copyright registrations for Tetris products in the U.S. and taking out trademark registrations for Tetris in almost every country in the world.

Alexey Leonidovich Pajitnov

Players lose a typical game of Tetris when they can no longer keep up with the increasing speed, or when the player can not find an appropriate solution to the Tetriminos they've been given, and the Tetriminos stack up to the top of the playing field. This is commonly referred to as topping out.

In computer science, it is common to analyze the computational complexity of problems, including real life problems and games. It was proven that for the offline version of Tetris, the player knows the complete sequence of pieces that will be dropped, i.e. there is no hidden information, the following objectives are NP-complete:

-Maximizing the number of rows cleared while playing the given piece sequence

-Maximizing the number of pieces placed before a loss occurs

-Maximizing the number of simultaneous clearing of four rows

-Minimizing the height of the highest filled grid square over the course of the sequence

Also, it is difficult to even approximately solve the first, second, and fourth problem. It is NP-hard, given an initial gameboard and a sequence of p pieces, to approximate the first two problems to within a factor of p1−ε for any constant ε>0. It is NP-hard to approximate the last problem within a factor of 2−ε for any constant ε>0.

To prove NP-completeness, it was shown that there is a polynomial reduction between the 3-partition problem, which is also NP-complete, and the Tetris problem.

More information: Grunge

According to research Tetris activity can also lead to more efficient brain activity during play. When first playing Tetris, brain function and activity increases, along with greater cerebral energy consumption, measured by glucose metabolic rate.

Scientists say that Tetris helps brain activity

As Tetris players become more proficient, their brains show a reduced consumption of glucose, indicating more efficient brain activity for this task.

Moderate play of Tetris, half-an-hour a day for three months, boosts general cognitive functions such as critical thinking, reasoning, language and processing and increases cerebral cortex thickness.

In January 2009, an Oxford University research group reported in PLoS ONE that for healthy volunteers, playing Tetris soon after viewing traumatic material in the laboratory reduced the number of flashbacks to those scenes in the following week. They believe that the computer game may disrupt the memories that are retained of the sights and sounds witnessed at the time, and which are later re-experienced through involuntary, distressing flashbacks of that moment. 

The group hopes to develop this approach further as a potential intervention to reduce the flashbacks experienced in post-traumatic stress disorder but emphasized that these are only preliminary results.

A study of Plymouth University's Cognition Institute shows that playing Tetris could give a quick and manageable fix for people struggling to stick to diets, or quit smoking or drinking.

Another notable effect is that, according to a Canadian study in April 2013, playing Tetris has been found to treat older adolescents with amblyopia, lazy eye, which was better than patching a victim's well eye to train their weaker eye.

The game has been noted to cause the brain to involuntarily picture Tetris combinations even when the player is not playing, the Tetris effect, although this can occur with any computer game or situation showcasing repeated images or scenarios, such as a jigsaw puzzle. 

While debates about Tetris's cognitive benefits continue, at least some researchers view it as a milestone in the gamification of education.

More information: Make Use Of

Tetris came along early and had a very important role 

in breaking down ordinary people's inhibitions in front of computers,

which were scary objects to non-professionals used to pen and paper. 

But the fact that something so simple and beautiful

could appear on screen destroyed that barrier.

 Alexey Pajitnov

RUDOLF NUREYEV & THE COLD WAR, DANCE TO FREEDOM

Rudolf Nureyev

Today, The Grandma is still playing with her new Space Invaders machine. She is a little exhausted after playing without stopping during hours and after having realized that the Anti Christ has returned to manage her current city during four more years. She is ready to fight against this cynic egocentric fake figure without surrender.

The Grandma has decided to watch something to relax herself and she has chosen some ballet performances of one of her two favourite dancers, Rudolf Nureyev -the other is Mikhail Baryshnikov.

Nureyev lived the years of the Cold War, the period of geopolitical tension between the Soviet Union with its satellite states (the Eastern Bloc), and the United States with its allies (the Western Bloc) after World War II. He defected from the Soviet Union on a day like today in 1961.

Rudolf Khametovich Nureyev, in Tatar Рудольф Хәмит улы Нуриев (17 March 1938-6 January 1993) was a Soviet ballet and contemporary dancer and choreographer.

Named Lord of the Dance, Nureyev is widely regarded as the greatest male ballet dancer of his generation.

Nureyev was born on a Trans-Siberian train near Irkutsk, Siberia, Soviet Union to a Tatar Muslim family. Nureyev began his early career with the Mariinsky Ballet in St. Petersburg.

He defected from the Soviet Union to the West in 1961, despite KGB efforts to stop him. This was the first defection of a Soviet artist during the Cold War and it created an international sensation.

He went on to dance with The Royal Ballet in London and from 1983 to 1989 served as director of the Paris Opera Ballet. In addition to his technical prowess, Rudolf Nureyev was an accomplished choreographer serving as the chief choreographer of the Paris Opera Ballet. He produced his own interpretations of numerous classical works, including Swan Lake, Giselle, and La Bayadère.

More information: The Rudolf Nureyev Foundation

Rudolf Nureyev was born on a Trans-Siberian train near Irkutsk, Siberia, Soviet Union, while his mother, Farida, was travelling to Vladivostok, where his father Khamet, a Red Army political commissar, was stationed. He was raised as the only son with three older sisters in a Tatar Muslim family.

Rudolf Nureyev in 1961

When his mother took Nureyev and his sisters into a performance of the ballet Song of the Cranes, he fell in love with dance. As a child he was encouraged to dance in Bashkir folk performances and his precocity was soon noticed by teachers who encouraged him to train in Saint Petersburg, named as Leningrad 1924–1991.

On a tour stop in Moscow with a local ballet company, Nureyev auditioned for the Bolshoi ballet company and was accepted. However, he felt that the Mariinsky Ballet school was the best, so he left the local touring company and bought a ticket to St. Petersburg.

Owing to the disruption of Soviet cultural life caused by World War II, Nureyev was unable to enroll in a major ballet school until 1955, aged 17, when he was accepted by the Vaganova Academy of Russian Ballet of Saint Petersburg, the associate school of the Mariinsky Ballet. The ballet master Alexander Ivanovich Pushkin took an interest in him professionally and allowed Nureyev to live with him and his wife.

Upon his graduation in 1958, Nureyev joined the Kirov Ballet, now Mariinsky. He moved immediately beyond the corps level, and was given solo roles as a principal dancer from the outset. Rudolf Nureyev regularly partnered Dudinskaya, the company's senior ballerina and the wife of its director, Konstantin Sergeyev. Natalia Dudinskaya, 26 years his senior, chose him as her partner in the ballet Laurencia.

More information: BBC

Before long Rudolf Nureyev became one of the Soviet Union's best-known dancers. From 1958 to 1961, in his three years with the Mariinsky, he danced 15 roles, usually opposite his partner, Ninel Kurgapkina, with whom he was very well paired, although she was almost a decade older than he was.

Nureyev and Kurgapkina were invited to dance at a gathering at Khrushchev's dacha, and in 1959 they were allowed to travel outside the Soviet Union, dancing in Vienna at the International Youth Festival. Not long after, he was told by the Ministry of Culture that he would not be allowed to go abroad again. In one memorable incident, Nureyev interrupted a performance of Don Quixote for 40 minutes, insisting on dancing in tights and not in the customary trousers. He relented in the end, but his preferred dress code was adopted in later performances.

Rudolf Nureyev & Zizi Jeanmarie, 1966

By the late 1950s, Rudolf Nureyev had become a sensation in the Soviet Union.

Yet, as the Mariinsky Ballet was preparing to go on a tour to Paris and London, Nureyev's rebellious character and a non-conformist attitude made him an unlikely candidate for a trip to the West, which was to be of crucial importance to the Soviet government's ambitions to portray what they felt was their cultural supremacy. Furthermore, tensions between Rudolf Nureyev and the Mariinsky's artistic director Konstantin Sergeyev, husband and former dance partner of Natalia Dudinskaya, were growing. After a representative of the French tour organizers saw Nureyev dance in Leningrad in 1960, the French organizers urged Soviet authorities to let him dance in Paris, and he was allowed to go.

Nureyev was seen to have broken the rules about mingling with foreigners and allegedly frequented gay bars in Paris, which alarmed the Mariinsky's management and the KGB agents observing him. The KGB wanted to send him back to the Soviet Union.

More information: The Guardian

On 16 June 1961, the Mariinsky group had gathered at Le Bourget Airport in Paris to fly to London. Sergeyev then took Nureyev aside and told him that he would have to return to Moscow, for a special performance in the Kremlin. Nureyev became suspicious and refused. Next he was told that his mother had fallen severely ill and he needed to come home immediately to see her. Nureyev refused again, believing that on return to the USSR he was likely to be imprisoned. With the help of French police and a Parisian socialite friend -Clara Saint, who had been engaged to the son of the French Minister of Culture Andre Malraux- Nureyev got away from his KGB minders and asked for asylum. Sergeyev and the KGB tried to discuss it with him but he chose to stay in Paris.

Within a week, he was signed up by the Grand Ballet du Marquis de Cuevas and was performing The Sleeping Beauty with Nina Vyroubova. On a tour of Denmark he met Erik Bruhn, soloist at the Royal Danish Ballet who became his lover, his closest friend and his protector until Bruhn's death in 1986.

Soviet authorities made Nureyev's father, mother and dance teacher Pushkin write letters to him, urging him to return, without effect. Although he petitioned the Soviet government for many years to be allowed to visit his mother, he was not allowed to do so until 1987, when his mother was dying and Mikhail Gorbachev consented to the visit.

Rudolf Nureyev

In 1989, he was invited to dance the role of James in La Sylphide with the Mariinsky Ballet at the Mariinsky Theatre in St. Petersburg. The visit gave him the opportunity to see many of the teachers and colleagues he had not seen since his defection.

In 1982, Nureyev became a naturalized citizen of Austria. In 1983, he was appointed director of the Paris Opera Ballet, where, as well as directing, he continued to dance and to promote younger dancers. He remained there as a dancer and chief choreographer until 1989. His artistic directorship of the Paris Opera Ballet was a great success, lifting the company out of a dark period.

When AIDS appeared in France's news around 1982, Nureyev took little notice. The dancer tested positive for HIV in 1984, but for several years he simply denied that anything was wrong with his health. However, by the late 1980s his diminished capabilities disappointed his admirers who had fond memories of his outstanding prowess and skill. Nureyev began a marked decline only in the summer of 1991 and entered the final phase of the disease in the spring of 1992.

In March 1992, living with advanced AIDS, he visited Kazan and appeared as a conductor in front of the audience at Musa Cälil Tatar Academic Opera and Ballet Theater, which now presents the Rudolf Nureyev Festival in Tatarstan.

More information: The Irish Times

Returning to Paris, with a high fever, he was admitted to the hospital Notre Dame du Perpétuel Secours in Levallois-Perret, a suburb northwest of Paris, and was operated on for pericarditis, an inflammation of the membranous sac around the heart.

At that time, what inspired him to fight his illness was the hope that he could fulfill an invitation to conduct Prokofiev's Romeo and Juliet at an American Ballet Theatre benefit on 6 May 1992 at the Metropolitan Opera House in New York. He did so and was elated at the reception.

Rudolf Nureyev

In July 1992, Nureyev showed renewed signs of pericarditis but determined to forswear further treatment. His last public appearance was on 8 October 1992, at the premiere at Palais Garnier of a new production of La Bayadère that he choreographed after Marius Petipa for the Paris Opera Ballet.

Nureyev had managed to obtain a photocopy of the original score by Minkus when in Russia in 1989. The ballet was a personal triumph although the gravity of his condition was evident. The French Culture Minister, Jack Lang, presented him that evening on stage with France's highest cultural award, the Commandeur de l'Ordre des Arts et des Lettres.

Nureyev re-entered the hospital Notre Dame du Perpétuel Secours in Levallois-Perret on 20 November 1992 and remained there until his death from AIDS complications at age 54 on 6 January 1993.

His funeral was held in the marble foyer of the Paris Garnier Opera House. Many paid tributes to his brilliance as a dancer. One such tribute came from Oleg Vinogradov of the Mariinsky Ballet in Saint Petersburg, Russia, stating: What Nureyev did in the west, he could never have done here.

More information: Stars & Stripes

Nureyev's grave, at a Russian cemetery in Sainte-Geneviève-des-Bois near Paris, features a tomb draped in a mosaic of an oriental carpet. Nureyev was an avid collector of beautiful carpets and antique textiles. As his coffin was lowered into the ground, music from the last act of Giselle was played and his ballet shoes were cast into the grave along with white lilies.

After so many years of having been denied a place in the Mariinsky Ballet history, Nureyev's reputation was restored. His name was reentered in the history of the Mariinsky and some of his personal effects were placed on display at the theatre museum in St. Petersburg.

At the famed Vaganova Academy a rehearsal room was named in his honour. As of October 2013, the Centre National du Costume de Scene has a permanent collection of Nureyev's costumes that offers visitors a sense of his exuberant, vagabond personality and passion for all that was rare and beautiful. In 2015, he was inducted into the Legacy Walk.

At the Paris Opera there is a tradition to organize a dance night as homage to Rudolf Nureyev every ten years after he died in 1993. The homage to Nureyev was scheduled on 20 March 2003 and on 6 March 2013 respectively because he was born in March.

More information: English Heritage

For me, purity of movement wasn't enough.

I needed expression, more intensity, more mind.

Rudolf Nureyev